The Design Of Toughened Glass Columns Physical Education Essay

The Design Of Toughened Glass Columns Physical Education Essay Glass has clinched the attention of engineers and architects in recent years despite its brittle nature. As well as its aesthetic allure, the increasing knowledge of this material allows structural boundaries to be pushed and endless possibilities to arise. Glass facades, beams, and stairs are some of the structures that have been explored with. However, the prospect of using a glass column as a structural component, as opposed to an ornamental role, is of increasing interest. Various structural glass types are available and have proven to be sufficient, but toughened glass reigns as the strongest type, yet its capability to spontaneously shatter can also prove to be a liability. What is Glass? Glass is an inorganic, non-crystalline, solid, transparent material, renowned for its brittleness. Its molecular structure attributes to its brittleness, making it weak in tension (Chen; Lui, Ch.29) and without an ability to redistribute load or absorb impact energy. Potentially, glass is very strong, even exceeding the strength of structural steel. However, due to glass having fairly low fracture toughness, this is only achievable when glass contains no defects, as freshly drawn fibre might be (Rice; Dutton, 33). Glass does not yield, instead it fractures and its failure is stochastic, meaning that prediction for failure is based upon risk or statistics (ISE, 11). Glass does not adhere rigorously to stoichiometry as crystalline materials do, due to the ability to incrementally alter the properties of glass continuously by adding components/substances to modify its properties. For instance, adding potassium oxide to silica will change the glass properties (Clare, Ch.23). Although described as a solid, glass is rather a subset of the solid state. It is essentially an elastic solid below its transformation region, i.e. the glass transition state, and a liquid above it, glass has the attributes of a liquid apart from the ability to flow (Clare, Ch.23). There is a range of intricacies inherent within glass composition; this will later prove to greatly explain the complexities of glass behaviour. A Look at Glass Chemical and Physical Composition Unlike many other materials, glass consists of a geometrically irregular network of silicon and oxygen atoms, with alkaline parts in between (fig.1.4) (Haldimann; Luible; Overend, 4). As glass is an inorganic product of fusion, it consists of a number of chemical components. The chemical composition of glass has a significant impact on glass viscosity, the melting temperature Ts and the thermal expansion coefficient ÃŽÂ ±T of glass (Haldimann; Luible; Overend, 4). One of the main attributes of glass is its resistance to corrosion by acid and water (Chen; Lui, Ch. 29). There is a vast variety of different types of glass, however, the most prevalent type of glass in construction (approximately 90%), is soda lime silica glass (Dewhurst Macfarlane and Partners), and for other special applications, borosilicate glass is used. However, depending on the purpose for the glass, other types are available, such as Lead glass, borosilicate glass, glass fibre, vitreous silica, alminosilicate g lass, alkali-barium silicate glass, technical glass, glass ceramics, optical glass and sealing glass, to name but a few (Glass Online). Borosilicate glass consists of mainly silica (70-80%) and boric oxide (7-13%) with small amounts of the alkalis (sodium and potassium oxides) and aluminium oxide. Borosilicate glass has a considerably low alkali content, and hence, has an appreciable level of chemical durability and shock resistance (Glass Online). The chemical components of soda lime glass are as follows: 70% 74% SiO2 (silica) 12% 16% Na2O (sodium oxide) 5% 11% CaO (calcium oxide) 1% 3% MgO (magnesium oxide) 1% 3% Al2O3 (aluminium oxide) (Glass Online) Regardless of the specific type, the main constituent of glass is silica sand (Chen; Lui, Ch. 29). Sand alone can be used to make glass at a temperature of 1700oC; but the addition of other minerals and chemicals significantly lowers the melting temperature (Glass Online). For instance, the melting temperature for pure silica is approximately 1710oC, but it drops to 1300-1600oC through the addition of alkali (Haldimann; Luible; Overend, 4). Glass consists of a network formers and modifiers Fig. 29.1. Silicon and oxygen ions are bonded together (formers) forming a three dimensional structural network of sodium, potassium, calcium and magnesium (modifiers) ions (Chen; Lui, Ch. 29). Sodium carbonate (Na2CO3), known as soda ash, is added to create a mixture of 75% silica (SiO2) and 25% of sodium oxide (Na2O), which will reduce the temperature of fusion to about 800oC (Glass Online). However, this concoction means the glass is produces water glass, meaning it is water-soluble. To give the glass stability, chemicals such as (CaO) and magnesium oxide (MgO) are added; which is achieved by adding limestone, which results in a pure inert glass (Glass Online). The viscosity of the liquid glass during the cooling phase increases constantly until solidification is achieved at about 1014Pas. The temperature at solidification is called glass transition temperature Tg and is about 530oC for soda lime silica glass. Contrasting crystalline materials, the transition between liquid and solid states occurs over a particular temperature range, instead of a single precise temperature (Fig. 1.5, Table 1.3). Small amounts of iron oxides are responsible for the greenish colour of soda lime silica glass. A reduced iron oxide content results in an extra clear glass, which is known as low iron glass, and is readily available (Haldimann; Luible; Overend, 6). Essentially, the composition of glass varies to appease a particular product and production method, which requires the raw materials to be weighed and mixed properly; as the consistency of the composition is vital in glass production (Glass Online). The essential physical properties of soda lime silica and borosilicate glass are summarised in Table 1.5. Optical properties depend on the thickness of the glass, the chemical composition, and the applied coatings. The most prominent of the glass properties, is its very high transparency within the visible range of wavelengths (ÃŽÂ »= 380-750nm). However, for different glass types, the exact profiles of non-transmitted radiation spectrum differ, but are in the wavelengths outside and near the infrared band (Fig. 1.6). A large percentage of UV radiation is absorbed as a result of O2 reaction in the glass, but long-wave infrared radiation (ÃŽÂ » The Making of Glass Essentially, glass is produced by rapid melt quenching of raw materials (reference); there are currently various methods by which glass is produced. The float process Fig 1.1 is the most practiced glass production method used today, which produces flat glass, attributing to 90% of the production worldwide. Although the steps vary, it is simply melting at 1600-1800oC, forming at 800-1600oC and cooling at 100-800 oC Haldimann; Luible; Overend, 1). The Pilkington Brothers introduced the float process in 1959. It has several advantages, such as low cost production, vast availability, superior optical quality, and allows for large stable glass panes to be manufactured. The production process is shown in Fig 1.2. Glass is produced by melted raw materials in a furnace at 1550oC. Subsequently, the molten glass is poured continuously at 1000oC on to a shallow pool of molten tin whose oxidation is prevented by inert atmosphere consisting of hydrogen and nitrogen. (Haldimann; Luible; Overend, 2 ). The glass floats onto the tine and spreads forming a smooth flat surface, with an even thickness of 6-7mm; it gradually cools and is drawn onto rollers, then entered into a long oven called a lehr that is heated at a temperature of 600oC. The thickness of the glass can be controlled within a range of 2-25mm, through adjusting the speed of the roller, whereby, reducing the speed increases the glass thickness. The glass is slowly cooled to prevent residual stresses being induced in the glass, after annealing, automated machines inspect the glass to check for obvious defects and imperfections. The glass can then be cut to a standard size of 3.21mÃÆ'- 6.00m, and stored. A disadvantage that arises from this method is that there is a discrepancy between the two faces of a glass sheet. Apparent diffusion of tin atoms into the glass surface occurs on the tin side, which could influence the behaviour of this surface when it is glued. The mechanical strength on the air side is greater tha n on the tin side, which occurs because of the transport rollers interacting with the tin side in the cooling area. This interaction with the rollers can reduce the strength of the glass as it can create surface flaws (Haldimann; Luible; Overend, 2). Fracture Mechanics in Glass As glass is unable to yield plastically ahead of fracture results in the fracture strength being highly sensitive to stress concentrations. To achieve accurate characterisation of the facture strength of glass, the nature and behaviour of the flaws must be integrated, as a result of surface flaws causing high stress concentrations (Haldimann; Luible; Overend, 49). The stress of glass is time dependent; yet, humidity causes stress corrosion resulting in flaws slowly growing when bared to a positive crack opening stress. Essentially, this is when a glass element is stressed below its momentary strength, fails after the time needed for the critical flaw to grow to its critical size (Haldimann; Luible; Overend, 49). These flaws are either inherent in the glass or a result of cutting, drilling, grinding, or an impact from the environment; humidity heightens the growth of cracks. Due to the cut edges in annealed glass being weaker than its flat surfaces, annealed glass beams are designed w ith lower stresses than glass plates. The onset of fast fracture is represented by this general equation: à Ã†â€™Ãƒ ¢Ã‹â€ Ã… ¡ (à Ã¢â€š ¬a)= à ¢Ã‹â€ Ã… ¡ (EGc) (ISE, 57) Where a is the half length of the crack, E is the Youngs Modulus and Gc is the toughness of the glass Gc has units of kJ/m2 and is the toughness of the glass, sometimes known as the critical strain energy release rate. The equation shows that fast fracture will happen when in a material subjected to a stress à Ã†â€™, a crack reaches some critical size a or alternatively, when material containing cracks of size a is subjected to some critical stress à Ã†â€™. This is a mathematical representation of the trend in annealed glass to be stronger under short-term loading rather than long term. The purpose of glass modification processes such as toughening and heat strengthening is to prevent glass from experiencing tension in surface to avoid crack growth, so that fracture mechanics calculations need not be considered Fig 5.3. Professor Inglis (1913) discovered that a slot, hole, or notch in a metal plate was likely to reduce strength by a greater value than that predicted from simply considering the reduction in tensile area. It was proven that the stress field near the discontinuity is exaggerated by an amount that is reliant upon the radius of curvature relative to its length perpendicular to the stress field. The discontinuities or randomly distributed flaws across the surface are known as Griffith Flaws. Griffith flaws are apparent on the surface of glass, but the strength of the glass is coinciding with the presence of visible defects, which is usually the origin of the cracks that occur under an applied tensile stress. Accidental contact can damage the edges of a glass plate more significantly than any other region of the glass. The deflection or bending of the glass is usually able to absorb the energy from an impact on a glass face but an edge impact is resisted by the full in-plane stiffness of t he glass plate or beam and produces greater damage impulse. Once load is applied, stresses develop and concentrate at the tips of flaws or cracks, which usually go undetected by the naked eye. Griffith claimed that crack propagation occurs if energy release on crack growth is adequate enough to supply all the energy that is needed for the growth of cracks. Mathematically this is stated as à Ã†â€™c=à ¢Ã‹â€ Ã… ¡EGc/à Ã¢â€š ¬a Where à Ã†â€™c is the stress required to fracture a plate with a crack of length 2a, E is Youngs Modulus and Gc is the critical elastic energy release ratio or toughness of the glass, with units of energy per unit plate thickness and per unit crack extension. This expression signifies the occurrence of fast fracture when a material is under stress that results in a crack of the size a. It is maintained by some that glass is able to reverse crack damage, i.e. heal a microcrack, if it reverts back to an unstressed state. On the other hand, the surface condition of glass sheet alters each time it is cleaned due to new microcracks surfacing. Therefore, the notion of damage reversal is up to the engineer to decide whether it is reliable in design (ISE, 57). Over time, momentary strength of loaded glass decreases, even if only subjected to static loads. This is a quintessential concept to grasp for the structural use of glass, and was demonstrated by Grenet (1899). Flaw and glass properties, stress history and the crack velocity-stress intensity relationship govern the growth of a surface flaw (Haldimann; Luible; Overend, 50). Structural Behaviour and Failure Characteristics of Glass Upon failure, glass does not yield, it fractures, and the failure is stochastic, meaning that the predicted failure is based on risk or statistical analysis (ISE, 11). However, glass is very strong, even stronger than steel. But the inherent low fracture toughness means that this optimum level of strength is only achievable when the glass is free from all defects. Ultimately, glass is brittle, without the ability to redistribute load or absorb energy (Rice; Dutton, 33). Due to the brittle nature of glass, it is important for the designer to have an insight into how the structure will behave if one or more of the glass elements fail; most importantly the safety implications should be assessed (ISE, 55). Fig 5.1 At low stress levels, the majority of materials tend to abide by Hooks law, in that stress and strain are proportional. Yet, a higher stress levels the material deforms plastically, but as glass is a brittle material, it simply fractures without warning instead. The mechanical properties of glass are displayed in Table 29.1 (Chen; Lui, Ch.29). The theoretical strength of glass is usually approximately a tenth of it elastic modulus. The density of the cracks rather than the theoretical breakage stress governs the failure stress of glass, whereby; glass compressive strength can reach a value of 10,000MPa, demonstrating that whilst in compression it is very strong. Conversely, in tension it fails, and this usually occurs when stress levels are less than 100MPa. It is the general consensus that glass failure originates from crack growth and surface flaws, where the stress is concentrated, as demonstrated in Fig 29.5 (Chen; Lui, Ch.29). To gain scope of how differently glass behaves relative to the most commonly used construction material, steel, is to observe the behaviour displayed in stress-strain curve: Glass molecular structure influences its mechanical properties, particularly its random irregular network of silicon and oxygen atoms. Its structure allows for no slip planes or dislocations so that macroscopic plastic flow transpires before fracture (Haldimann; Luible; Overend, 49). Glass failure is most likely to be initiated by surface cracks, because these tend to have the worst geometries and are subjected to the highest stresses due to bending. If the loads to which the glass is subjected do not create enough surface tension to overcome the surface compression, no crack will propagate. Toughening, therefore, increases the effective strength and impact resistance of the glass. Should an external load overcome the precompression and cause a crack to propagated, then the stored energy due to prestress will cause the cracks to spread immediately in all directions and the pane of the glass will fragment explosively (Rice; Dutton, 33). Static fatigue of glass, also known as sub-criti cal crack growth is a phenomenon of glass. An applied sub critical stress causes cracks of flaws to slowly grow with time, until a length is reached, at this point the stress intensity at the crack tip reaches a critical value. Consequently, rapid fracture occurs due to the highly strained atomic bonds swiftly breaking at the crack tip. Stress corrosion is a term used to describe the relationship between the crack growth velocity and the stress intensity factor. Apart from applied stress, there are a number of factors that hasten slow crack growth, such as alkaline solutions and increasing temperature (ISE, 56). Plastic flow is not possible in glass, therefore when the glass surface is in a state of tension; the flaws produce high stress concentrations. The flaws are random and can take any path; therefore the failure strength can only be determined through statistical analysis. Therefore, the basis of risk of fracture of glass that is determined does not give assurance that the glass can withstand the designed load. Strength of glass relies on the load duration and environmental conditions; Fig 29.6 shows the strength-time relationship (Chen; Lui, Ch. 29). The time to failure and applied stress relationship is expressed mathematically as à Ã†â€™nT= constant Where à Ã†â€™ is stress T is duration and n is a constant (ISE, 56). The value of n varies, and Sedlack (1995) as well as Pilkington Glass Consultants recommend n = 16 for design purposes. This equation suggests that loads applied at an exceedingly long duration will allow allowable stresses to decrease to insignificant values. However, in reality, this is not true (ISE, 56). Unlike steel that yields and flows when locally overstressed, glass breaks when it is overstressed. For that reason, it is vital that the designer attempts to eradicate possible design features that may result in stress concentrations. Such as bolted glass has been developed in such a way that, stress concentrations are avoided around the bolts; this attention to detail cannot be readily detected (ISE, 58). To avoid force being transmitted from glass to another material, as this causes stress concentrations to develop; soft setting blocks, fibre gaskets, and protective brushes have been implemented to limit this (ISE, 58). Glass is almost perfectly elastic, linear and is isotropi c, and is not subjected to fatigue (Haldimann; Luible; Overend, 8). Glass only fails by brittle fracture, and cycling loading can cause the growth of cracks. Most materials have a fatigue limit, whereby there is stress amplitude where facture does not happen or fracture only happens after a great number of cycles (>108). Additionally, although many materials have a fatigue ratio, which is the ratio of the fatigue limit to yield strength, but since glass does not yield, this attribute is obsolete (ISE, 58). As glass fails in tension or by buckling, the highest tensile stresses that occur from applied loads should be considered when finding the elastic stability of glass element. Applied compressive stresses can cause tensile strains, but tensile strains can even occur as a result of the Poissons effect from compressive stresses (ISE, 60). Glass failure occurs when the tensile stress is equal or greater than the characteristic strength, which can be calculated using Eqn 29.5. The memb rane stress is constant across the thickness of the plate, whilst the bending stress can be taken as varying linearly. Thus, superimposing the membrane and bending stresses can determine the total stress on the glass (Chen; Lui, Ch. 29). Furthermore, the deflection of glass elements is an important aspect to consider; and such behavioural patterns like toughened glass deflecting more than annealed glass (even when of the same strength) due to toughened glass being considerably thinner, should be taken into consideration (ISE, 56). Glass plates are typically thin so they demonstrate large displacements. The use of thin plate linear bending theory will produce incorrect results. Therefore, the large deflection theory should be used instead to calculate the maximum stress when checking stress against failure. Failure generally is taken to be at the point when the maximum tensile stress equals the glass fracture stress (Chen; Lui, Ch.29). Glass can be quite sensitive to any impact and will result in fracture; the common causes of glass breakage are: Excessive stress form wind pressure or other loads Thermal stress due to differential temperature on different parts of the pane Buckling due to large compression Surface or edge damage Deep scratches or gouges Severe weld splatter Direct contact with metal (e.g. window aluminium frame) Impurities like nickel sulphide (NiS) Excessive deflection bringing glass in contact with other hard objects. (Chen; Lui, Ch. 29) Hence, the strength of glass relies on these aspects: the duration of the applied load, environmental conditions, humidity, size of the stressed area, the distribution of stresses across the stressed area, the condition of the surfaces and edges of the glass (ISE, 57). Prestressing glass, notably by heat-strengthened and toughened are the two basic types, enables the glass to maintain compression on the surface, therefore, eliminating crack propagation (ISE, 59). Survival probability of scratched glass loaded at a constant rate Eqn; Time dependence of glass strength Eqn Fig 5.4 Fig 5.5 Fig 5.6 The Different Types of Structural Glass Glass, itself, is highly susceptible to fracture, which results in a lot of shattered glass, and ultimately, health and safety implications. The fracture of glass stems from the surface flaws. Thus, the industry has developed various modification methods to achieve an increase in the practical strength of glass, by introducing local high compressive stresses near its surfaces (Chen; Lui, Ch.29). By common practice, these modifications are usually implemented on float glass. Tinted Glass Tinted glass is also known as heat-absorbing glass, and is produced by colorant being added to normal clear glass. Light transmittance varies depending on colour and thickness, with a range between 14 to 85%. As a result, tinted glass is not and heat-strengthened glass is typically used when making tinted glass (Chen; Lui, Ch.29). Coated Glass Placing layers of coating onto a glass surface makes coated glass, and there are two types: the solar control (reflective) and the low emissivity types. Structural strength of coated glass is only indirectly affected when the thermal stress is altered, but coated glass is more associated with its energy absorption and light transmission attributes. Therefore, to prevent excessive thermal stress, heat-strengthened glass should be used to produce coated glass (Chen; Lui, Ch.29). Wired Glass A common misperception is that wired glass is stronger than unmodified annealed glass, due to the wires being seen as reinforcement. However, the wires actually induce cracks and weaken the glass. Yet, wired glass is able to hold together upon being broken (ISE, 22). Wired glass is produced when a steel mesh is implemented onto the molten glass during the rolling process (the rolling portion of the flat glass process). It has a high rate of breakage due to sunlight, and hence is weak in resisting thermal stress. Although it is still weak in resisting thermal stress, polished wired glass is used for fire rating since after it breaks, it sticks to the wire mesh and prevents smoke passing. Figure 29.8 shows a damaged wired glass panel under sunlight (Chen; Lui, Ch.29). Annealed Glass Annealed glass panels do not have any heat treatment (Chen; Lui, Ch.29); it is produced using the float process (as described previously) (ISE, 22). It is usually used when large glass panels need to be used, and it is too large for any heat treatment (Chen; Lui, Ch.29). The behaviour of annealed glass is typically perfectly elastic until fracture occurs. Upon fracture, large, sharp shards emerge which are dangerous. However, annealed glass panes do not spontaneously fracture, and due to alternate load paths across the glass pane, it may not fall out of its frame upon failure. Although there is no creep or fatigue in the metallurgical sense, slow crack growth occurs as a result of cyclical loading, whereby, if this glass is under permanent loading, the deformation increases with below 3% over a 50-year period. Imposed strains, such as bending and thermal stresses, as well as instant impact, causes elastic deformation resulting in brittle fracture of annealed glass (ISE, 22). Annealed glass is not very strong, so it is weak in thermal resistance. The allowable stress is approximately 15N/mm2 (Chen; Lui, Ch.29). Fig 2.4 Fig 2.5 Fig 2.6 Heat-Strengthened Glass Heat-strengthened glass is created using a similar process to toughening, with the exceptions that there is a lower cooling rate (Haldimann; Luible; Overend, 12) and the level of the produced prestress is lower. The fracture behaviour, however, is more akin to that of annealed glass rather than toughened (ISE, 24), with larger fragments than that of thermally toughened glass (Haldimann; Luible; Overend, 12). The compressive surface stress for heat-strengthened glass lies in a range between 24 and 69N/mm2 and European Standards quote that the pattern of breakage ranges between 25 to 40N/mm2 (ISE, 24). Heat-strengthened glass is commonly used in laminated glass assemblies, but the nature of its large fracture pattern causes a significant remaining load-bearing capacity upon failure of the glass. The stress gradient depends on the thickness of the glass and as the glass must be cooled down gradually, thus, thick glasses (exceeding 12mm) cannot be heat-strengthened using the toughening p rocess (Haldimann; Luible; Overend, 12). Laminated Glass Laminated glass is two or more glass panes bonded with an interlayer of polyvinyl butyral (PVB) or resins, such as acrylic. The thickness of the interlayer varies between 0.4mm to 6mm. A disadvantage of laminated glass is the validity of composite action. Although usually only two layers are bonded, over 25 layers have been effectively bonded coming at 100mm thick. Laminates can integrate many thicknesses and arrangements to suit a certain requirement. Most importantly, many different types of structural glass can be arranged in the laminated formation, including toughened, annealed, heat-strengthened and bent glass for example. However, toughened and heat-strengthened glasses both cause small amplitude waves as a result of the rollers used in the process. This in turn, enhances the separation between the laminated glasses and ultimately the PVB is impractical. Therefore, resin laminating should be instead. When using a PVB interlayer, the sheets of glass have the PVB interjected bet ween them and then this sandwich travels through an oven of about 70oC, and then passes between rollers which squeeze out the excess air from the bonding. The laminated glass is then placed in an autoclave, heated at 140 oC and at a pressure of 0.8N/mm2. It is possible to manufacture laminated glass at a maximum of 6m by 3m. In resin laminating, the two principal resins are acrylic and polyester. The glass sheets are held together at a right distance apart using double-sided tape around the perimeter. The resin can then be poured in between the two sheets, and once the air has been extracted the open edge can be sealed, and the laminate is stored horizontally to allow the resin to cure and solidify. The curing occurs through UV light or chemical reaction. The size that can be manufactured using this method is dependable on available glass pane sizes (ISE, 24). The structural behaviour of the laminated glass varies, depending on the duration of the load. Hooper (1973) demonstrated that the duration of the loads affected the behaviour of the laminate. With short-term loads the laminate acted compositely, whilst with long-term loads, the load was shared between the two glass sheets, in proportion to their relative stiffnesss, as a result of the deformation of the interlayer (ISE, 24). To determine this behaviour, the deflection of the panel under a specific load should be measured and then compared to the deflection calculated using finite element software. This would allow for the equivalent thickness used in the software to be adjusted to give the same deflection measured, in order to determine the equivalent thickness of the laminated glass pane that should be used for optimum design (Chen; Lui, Ch.29). An increase in the temperature, results in the interlayer softening and a reduction in the composite behaviour. Laminated glass is highly valuable as it offers various performance benefits. For instance, if one or both of the layers are impacted and breaks, the interlayer prevents penetration and allows any broken glass to stay bonded to the interlayer. Additionally, an increase in the thickness of the interlayer increases the penetration resistance of the glass (ISE, 24). Fig 29.9 Displays laminated glass behaviour once broken (Chen; Lui, Ch.29). Toughened Glass Chemically Toughened Glass: Chemically toughened glass implements the principle of a compressive surface layer preventing crack propagation, where the compressive layer is a result from an ion exchange process. Therefore, flat glass that contains sodium ions is immersed in a molten salt bath (electrolysis baths (ISE, 23)), of potassium nitrate. As the temperature of the molten salt is insufficient to permit structural relaxation, the potassium ions force themselves into the sodium sites, consequently, putting the surface under compression (Clare, Ch.23). Although it is an advantage that unlike thermal toughening, thinner glass sheets can be toughened, it results in thinner compressive layers, which are less robust than the thicker layer created through thermal toughening (ISE, 23). Also, the strength of glass can be increased by ten times depending on glass composition (Clare, Ch.23). Thermally Toughened Glass: Thermal toughening of glass is achieved by heating annealed (float) glass plate to about 620-650oC, whereby it begins to soften at this point (ISE, 23). The outer surfaces are then cooled rapidly by cooled air blasts, and the exterior layers quickly cooled and contracted. A thin layer of high compress stress the surface occurs, with a region of tensile stress at the centre of the glass (Fig 29.7). The parabola represents the stress distribution across the thickness of the glass pate, which is also in self-equilibrium. The physical properties of the particular glass used and the geometric shape of the glass governs the exact shape of the curve. Toughened glass has a bending strength is three to five times

Three Characters with Good Intentions in Shakespeares Romeo and Juliet :: Shakespeare, Romeo and Juliet

Based on the impulsive, irrational Veronese society, many of the characters in Romeo and Juliet believe that they are doing everything â€Å"all for the best.† Three characters which exemplify this fully are Lord Capulet, Tybalt and Friar Lawrence. All the characters are products of their own society, Veronese society. Status is everything, money buys anything. Woman must marry well and produce many offspring. Men believe strongly in defending their honor by any means available especially violence. When there is a fight in the market place, Capulet rushes to fight for his honor, â€Å"my sword I say, old Montague is come...† Capulet denies Paris’ request to marry Juliet â€Å" and too soon marred are those so early made,† acting for his own good because he wants Juliet to produce many offspring to carry on the Capulets bloodline, since she is his only surviving child. When at the ball Capulet demands Tybalt to let Romeo be,† content thee, gentle coz, let him alone,† but this just fuels Tybalts anger towards Romeo, which eventually ends up in Tybalt causing his own death. Capulet believes he is giving his child the best when he announces her engagement to Paris† she shall be married to this noble earl,† and believes Paris will make a good husband for Juliet. When Juliet refuses Capulet thinks it best to threaten her, â€Å"I will drag thee,† but this just makes Juliet turn to more drastic measures. When asked by Benvolio to make peace in the streets, Tybalt bluntly responds,† talk of peace, I hate the word. As I hate hell all Montagues.† This is the attitude of Tybalt throughout the play. He believes he is doing all for the best and uses violence as his tool. He gets angry at the ball with Romeo being there, â€Å"villain as a guest,† and believes it best to defend his family’s honor by later taking revenge. When Tybalt finds Romeo, he thinks it best to fight him and when he ends up killing Mercutio he believes he has done his duty by causing Romeo the same hurt he has brought Tybalt, â€Å"the injuries that thou hast done me.† Friar Lawrence is by the far the character that displays â€Å"working for the best,† the most. The three main events are the marriage, the plan and the death, all three of which the friar is very involved. The friar originally marries Romeo and Juliet in hopes that the feud between the two families will end, â€Å"to turn your households’ rancor to pure love.

Ethics of Offshoring Novo Nordisk

Critical issued of the appropriateness of conducting clinical trials in emerging countries has arisen over years. Being a leading company in biopharmaceutical industry, Novo Nordisk faces the critiques of whether it is justice to offshoring their clinical trials in developing economies. With the consistency of ethical principles brought up by Novo Nordisk, the company would be able to move their trials into emerging economies with the best interest for stakeholders. I will also propose ideas to Mr, Dejgaard for possible approach to media as well as the practices that Novo Nordisk could have changed over time at the end. Conducting Clinical Trials in Emerging Economies With Utilitarian approach, every party has different perspectives in the outcome of an action. In this case, we have shareholders, employees, customers, supply chain, government and local communities, with secondary stakeholders of media, special interest groups and NGOs. For customers, government and local communities, they emphasize more on the proof of efficacy and safety of medical products. While shareholders, employees, supply chain care more of the profitability as a whole in general. As a result, Novo Nordisk will be better off maximizing its profits while holding their ethical justice for conducting clinical trials in emerging countries. Economic Aspect As the Nobel prize winner, Milton Friedman pointed out that making profit will be the first priority for business to fulfill social responsibility, Novo Nordisk has every right to maximize its best interest for its stakeholders include shareholders, employees, customers, suppliers, governments and local communities. From financial performance stand point, conducting clinical trials in emerging economies benefits Novo Nordisk from saving costs, accessing to larger demographic participant, obeying less strict rules applied, and establishing efficacy in different environmental onditions. Ethical Aspect On the other hand, firms should consider the corporate social responsibility brought by the society. Firms definitely need to incorporate their highest moral standards to build trust and reputation for themselves in order to better off in long run. Novo Nordisk always follows the regulation from Helsinki Declaration with other international ethical guidelines. They made sure that the inte rest and well-being of the trial subject should always transcend over the interest of science, society and commerce. Decision Principles Even though I think conducting clinical trials in emerging economies is beneficial to the firm, Novo Nordisk should still follow below guidelines for this major decision to protect its own reputation and serve the best interest for every stakeholder: †¢ Execute clinical trials when the internal organization is well established and external environment is proper regulated in emerging countries. †¢ Conduct placebo clinical trials when they are scientifically and ethically justified. †¢ Ensure the human rights of the participants in emerging countries associated with the predictable risks Responses to The Media I understand that Mr. Dejaard holds a high ethical stands, and is not interested in misleading the public or ethical dissembling in the response. It is also important to clear up the actions Novo Nordisk has taken for the past years and give public a clear picture of how the firm is operating. If a journalist is inviting for an interview, Mr. Dejaard should present himself into the public and response to the inquiry people have, otherwise, absence will only show irresponsible image that he might try to escape from the issue. Medical Ethics I will suggest Mr. Dejaard to pull out historical data indicating that the random checks investigated from Food and Drug Administration (FDA), the American and European authorities have never identified ethical problems in clinical trials in emerging economies. Second, assert the ethic codes from their company will help the publics to receive the image of Novo Nordisk has complied with the Helsinki Declaration of the World Medical Association. Ethical Business Media might inquiry the fairness of conducting placebo experiment in emerging countries by Novo Nordisk based on the industry trends in recent time. Mr. Dejaard could response to them that Novo Nordisk usually stay away from placebo trials, and only used in phase 1 trials which only healthy volunteers participated. Also, Novo Nordisk framed new business ethics policy in 2005 with generally accepted high standards while training managers and employees attending workshops and offering e-learning policy. To better respond to the media, Mr. Dejaard could also indicate that Novo Nordisk will try to implement some new action plan that could benefit stakeholders as a whole in order to minimize ethical conflicts. I suggest the following action plan for Novo Nordisk to benefit them in long run. Action Plan Enhance Auditing System To build trust for the stakeholder for Novo Nordisk, I believe the firm should develop a more solid auditing system. Instead auditing 10% of all trials, Novo Nordisk should increase the rate up to 50% or more. From a public view, 10% of investigating in all trials is not sufficient enough to prove that the trials are ethical conducted. With the increasing number of trials being audited and investigated, the quality of the clinical trials could be better controlled. Build up Placebo Experiment Standard In the â€Å"Clinical Trials: Novo Nordisk’s Position,† it pointed out that placebo will only be used as comparator when scientifically and ethical justified. It is quite unclear for public to know what would be an appropriate placebo experiment for Novo Nordisk to conduct while proven therapy is available. It is important to insiders to identify whether or not conducting placebo experiment under certain circumstances will have any additional risk and irreversible harm.

Of Mice and Men †Character study of Curly’s wife Essay

The novel ‘ Of Mice and Men’ is set in America and is about two travelling workers who have been chased off one ranch because Lennie, one of the men did not know how to behave himself. Lennie is large, heavy and ponderous and George is small quick, dark, sharp and restless. Another tragedy happens on the ranch like in weed because Lennie used his strength to kill Curley’s wife. I can sympathise with Curley’s wife although she was a flirt with the other men she was not expecting to be killed by Lennie. We first meet Curley’s wife in chapter two. She is described as heavily made up and wears tarty red shoes. She poses her figure outlined in the doorway of the bunkhouse and is always aware that men are looking at her. This makes me think that she is just looking for attention from the men. George shows the reader that he does not like Curleys wife because George tells Lennie that she is jailbait and for Lennie to stay away from her. Lennie see’s her as an attractive young lady but she is really just a threat to the men on the ranch. In chapter three there is a big fight involving Curly and Lennie. Curley has not liked Lennie since he was looking at Curleys wife so Curley just lost his rag and started punching Lennie but then Lennie just reached for Curley and just grabbed his hand and started squeezing his hand and his hand crumbled in Lennies hand, George told Curley to tell everybody that he got his hand caught in the machine and that is what he told everyone. This just shows how Curley’s wife is acting like a tart and a flirt to get all the men in trouble with Curley.Curley feels insecure because of his wife’s behaviour. In chapter 4 Curleys wife was heavily made. I can sympathise with her because all she is trying to do is make some friends on the ranch but every time she tries to talk to someone they all think she is trying to flirt because she is desperate for attention because she has got an unhappy marriage with Curley and that the men think that she is trying to get them in trouble with Curley.I fell sorry for Curleys wife because on the ranch she was all alone. In chapter 5 we learn that Curleys wife had a dream to be in the movies. I do feel sorry for Curley’s wife because she could have been in the movies but that was just a pipe dream because now she is stuck on the ranch married to Curley with no friends. Curley and his wife have only been married for two weeks and already they both hate it being together on the ranch. I think Steinbeck is trying to get across to the readers that she has no one in the whole world that cares for her. Her death was brutal and quick, at first lennie was just playing with the pup then he broke its neck and that is what he done to Curley’s wife. My final thoughts on Curleys wife is all she was trying to do is make friends on the ranch but she just got pushed out everyone. In chapter six it is hard to feel sympathy for her because she was flirting with the men but she did not deserve to be killed by Lennie. I feel sympathy for Curley’s wife although she was a big flirt and she got treated badly by Curley, she did not deserve to be killed. I think Steinbeck included Curley’s wife in the story because I think that she makes the story interesting because she is the story.

Constitution of 1917 essays

Constitution of 1917 essays Nationalism hit home in Mexico when the Constitution of 1917 was written. Neocolonialism was now at an end when Porfirio Diaz was over thrown in 1910. During this time, the masses and especially the middle class wanted a total social, economical, and political reform in Mexico. After Diaz left, Mexicos politics became very unstable and was marked by power struggles and revolutions. Finally, a movement that was better organized, involving more urban and middle classes, lead by Venustiano Carranza was able to take power and draft the Constitution of 1917. The Constitution of 1917 was a remake of the constitution that was created by Benito Juarez in 1857. The ideas that had embodies this constitution were long outdated and did not represent the new nationalistic views of the people. Three important points presented in this constitution concentrated on topics such as religion, education, nationalization of industries, and the rights of workers that had made up much of the masses. For example, article 3 stated that primary education must be mandatory and free. Most importantly, it must be free from all religion affiliation and influence. This was a major change in social reforms. Previously, the Catholic Church had dominated the sector of society, but as other articles of the Constitution of 1917 would imply, the church would lose nearly all of its power. Priest would not longer even be allowed to wear their religious clothing in public. Another important objective of the constitution was nationalization of lands and industries. This would be included in article 27 which stated that all minerals such as gold, silver, oil and water located under the soil would be now owned by the state. This article created many eruptions because previously these rights had rested in the hands of foreign companies such as those in the United States, a very powerful influence on Mexico during these times. For Mexico, Article 27 provided...

Individual, community and macro points of view on migration Essays

Individual, community and macro points of view on migration Essays Individual, community and macro points of view on migration Essay Individual, community and macro points of view on migration Essay Migration does not always coupled with growth unless it was given proper measures and economic restructuring (Appleyard: 1992; Hammar et al. : 1997;Ghosh: 1998). The major reason for migration is considered to be for economic purposes. History showed evidences that the immigrants and their descendants play an important role in the economic growth of the host countries. Developed countries which welcome immigrants become richer and richer. In addition to the openness of the immigrants to all types of work, they can also work under cheap labor that the natives will reject.This allows the old businesses such as textiles and garments to still exist adding to the income of the host country. Migration of skilled workers will further strengthen the skills and talents pool of the country. These enhance their productivity and economical gains. Simultaneous with the gain of brain and skills of the host country is the loss of the brain and skills of the country of origin which are oftentimes the poor countries or the developing countries. This may bring brain drain or loss of the trained, educated and skilled individuals which will inhibit the development of the native country or country of origin.Dependence to foreign countries will be one of the consequences of this which will post negative effect on productivity and economy of the native country. Some researchers, however, regarded immigration to contribute to economic growth of the native country through the remittances that the immigrants send to their family. These remittances are the major source of foreign exchange in developing countries which alleviate the poverty line. According to the International Migration Data, global remittances to developing countries worldwide are estimated at $204 billion per year.(International migration data) The countries who registered the highest remittances are Mexico, India, Philippines, Egypt and Morocco. ( International migration data) This enormous value made the home countries considered their emigrants to have the major role in improving its economy. It contributed to the fluidity of cash flow and development of business sectors. Realization of the major participation of emigrants’ remittances made the home government sets priority regarding the welfare of these workers.Researches showed that these remittances tend to be invested to the home country for housing, consumption, land, loan payment and savings and to business which the home government targets. (Addy, p. 16) Their families are well supported in establishing their own business in the country and given other privileges. The increasing value of remittances and the business established are expected to balance the effect of brain drain, the source country is experiencing. At the personal level, the immigrant faces a quandary on culture and environment.Furthermore, in the foreign land, he is also vulnerable to racial discrimination, exploitation and deportation. He is forced to embrace whatever is offered to him for a common good. Coping with these adaptations to host country’s norms and practices simultaneous with physically adapting to climate and health conditions requires a great level of energy and determination. Absence of the family members also adds to the burden the immigrant is experiencing. New technologies of communication help in this endeavor which makes it easier to gain emotional stability.Both positive and negative effects do not limit to the individual alone. Whatever happens to the immigrant in the host country will definitely affect his family in the home country. Studies showed that the family is more affected when the migrant worker is a woman for basically she is the homemaker and takes care of the children. Nowadays, there is an increasing number of migrant women accounting for 48 per cent international migrants. Some effects radiates from the family to the community. The flow of income, for example can be manifested in the economics within the area.This will be radiated further to the home country reducing the poverty. They also contribute to development through investments, business or entrepreneurial activities and the return of newly developed skills and knowledge. The community of the host country, on the other hand, may initially be skeptical of accepting the immigrant. On their point of view, the immigrants can change and influence their economy and other values. A community which does not allow immigrants may be giving up the values, education, perhaps specialization and other benefits brought by the immigrants.

Business overview of British American Tobacco

Business overview of British American Tobacco British American Tobacco (BAT) is the world’s second largest tobacco group by global market share. BAT produces cigarettes demanded by one-eighth of the world’s one billion adult smokers and this particular company is holding robust market position in each of their regions. Besides that, BAT has leadership in more than 50 markets. Based on last year’s performances (2009), BAT’s subsidiaries enabled the worldwide government to gather more than  £26 billion a year in taxes, including excise duty on their products which total up to almost nine times the Group’s profit after tax. BAT, which was founded in 1902, has existed as a significant global presence for over 100 years. By 1912, the company had become one of the world’s top dozen companies by market capitalization. This company works with thousands of tobacco farmers worldwide, producing some 724 billion cigarettes through 50 cigarette factories over 41 countries. The company employs more than 600,000 people worldwide. BAT’s workforce is of multi-cultural and they have devolved structure, with each local company having wide freedom of action and responsibility for their own operations. Within a framework of principles, standards, policies, strategies and delegated authorities, decisions are made as close as possible to the local stakeholders of each business. BAT operates according to responsibility seeing that their products pose risks to health. The business stresses on managed responsibility as it is integral to their strategy and through dialogue with their stakeholders, they are working towards commercial objectives in ways consistent with changing expectations of a modern tobacco business. This international tobacco group is the only group with a significant interest in tobacco leaf growing. Their companies run leaf programmes providing direct agronomy support to farmers, covering all aspects of crop production and environmental best practice. In 2009, the group purchased about 400,000 tonnes of tobacco leaves, grown by more than 250,000 farmers. BAT ensures the employees’ welfare. The company has specially carried out a global employee opinion survey also known as â€Å"Your Voice† to give them a secure and confidential way to voice their opinion about working at British American Tobacco. BAT’s business starts with their consumers and brands. The company focuses more on meeting preferences of adults who have chosen to consume tobacco and differentiating their brands from their competitors rather than encouraging people to start smoking or to smoke more. The business’ portfolio of more than 250 brands is based on distinct ‘must-win’ consumer segments which are: international, premium, lights and adult smokers aged below 30. ‘Dunhill’, ‘Kent’, ‘Lucky Strike’ and ‘Pall Mall’ are the four Global Drive Brands which cover the premium and value for money price segments. They grew by 4 per cent in 2009 (8 billion more cigarettes). The business is also increasing the profile of Vogue in the super premium segment and Viceroy, a leading low price international brand besides developing their Global Drive Brands. The growth of their brands is driven by innovation ranging from filters to flavours and packaging to cigarette formats. The business provides a mix of brand balanced between premium, mid-price and low-price. Besides that, the business applies the four managerial functions in its organization management; planning, organizing, leading and controlling. We have also interviewed a manager of British American Tobacco Singapore for further understanding.