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Revision Questions Booklet MATERIAL FROM SEMESTER 1 ONLY This document contains additional questions for practice and revision, both multiple choice questions and short answer questions. Answers are provided but only at the end to allow you to complete these in something approximating exam conditions. Written answers are brief, and more detail may be needed in an exam. Although numerical answers are given where necessary, it is up to you to do the working out. Please note that in an open book final exam, certain questions that simply require recall of course material without calculation or analysis will not usually be asked – however, some questions of this type are present below for completeness. Multiple choice: 1. What is the configuration of electrons in fluorine (F) a. 1s2 2s2 2p6 3s2 3p6 b. 1s2 2s2 2p6 c. 1s2 2s2 2p5 d. 1s2 2s2 2p6 3s2 3p6 4s1 2. The n=3 principal energy level, or shell, contains s, p and d subshells. How many electrons are present in the n=3 principal energy level a. 8 b. 16 c. 10 d. 18 3. Zinc (Zn) has four stable isotopes, listed below with their relative abundance. Calculate the relative atomic mass for zinc. 30 64Zn – 48.8% 30 66Zn – 28.1% 30 67Zn – 4.2% 30 68Zn – 18.9% a. 65.6 b. 65.0 c. 65.4 d. 66.0 4. Which of the following sets of features are characteristic of ionically bonded materials a. The bonds between individual molecules are weak, and only tend to have an effect at relatively low temperatures. b. They are often ductile, form regular crystal structures and conduct electricity when solid. c. They can be solids, liquids or gases at room temperature and pressure. Individual molecules have fixed geometries, but these do not often form large scale crystals. d. They are ceramics, have regular crystal structures with a high melting point and are often soluble in water. 5. The elastic modulus or ‘stiffness’ of a material can be determined by: a. The slope of the linear part of the stress-strain curve b. The stress value that represents the maximum of the linear part of the stress-strain curve c. The stress value corresponding to the maximum value of the stress-strain curve d. The integral of the area under the stress-strain curve 6. In a metal forming process, a metal component is subjected to a tensile stress in two dimensions ( 1 and 2) and a compressive stress in the other ( 3), as shown in the diagram. What is the strain in the direction of the compressive stress [ = 0.28, E = 2 GPa] a. -0.265 b. -0.025 c. -0.215 d. -0.015 7. What is elastic strain recovery a. It is the small, permanent plastic strain at which yield stress can be measured accurately. b. After final fracture of a specimen, the resulting pieces of the specimen are no longer loaded and decrease in length elastically c. It is the residual, permanent strain in a specimen that has been stressed beyond yield (i.e. plastic strain has occurred) and then unloaded d. It is the reduction in strain when a specimen that has been stressed beyond yield (i.e. plastic strain has occurred) is unloaded 8. The figure below shows impurities (dark circles) added to an elemental metal (white circles). Which result(s) represent interstitial solid solution(s) a. Result IV only b. Result II only c. Result I only d. Results II and IV = 500 MPa = -250 MPa = 500 MPa 9. An iron-carbon alloy that is 1.00% C by weight is slowly cooled from 1600oC (see phase diagram below). Which of the following best describes what will happen a. It will start to solidify at about 1465oC and finish solidifying at about 1353oC b. It will start to solidify at about 1493oC and finish solidifying at about 1147oC c. It will all solidify at once at about 1147oC as this is the eutectic point d. It will start to solidify at about 800oC and finish solidifying at about 727oC 10. Consider the Fe-C phase diagram. An alloy that is 1.00% C by weight is slowly cooled from 1000oC to 700oC. Which of the following best describes the result a. A 2-phase mixture of ferrite (0.76% C) and Fe3C cementite (6.70% C) b. A 2-phase mixture of ferrite (0.76% C) and Fe3C cementite (2.14% C) c. A 2-phase mixture of ferrite (0.02% C) and Fe3C cementite (4.30% C) d. A 2-phase mixture of ferrite (0.02% C) and Fe3C cementite (6.70% C) 11. Consider the Fe-C phase diagram. An alloy that is 1.00% C by weight is slowly cooled from 1000oC to 700oC. Which of the following best describes the result a. In mass fraction it will be about 96% ferrite and 4% Fe3C cementite b. In mass fraction it will be about 85% ferrite and 15% Fe3C cementite c. In mass fraction it will be about 69% ferrite and 31% Fe3C cementite d. In mass fraction it will be about 15% ferrite and 85% Fe3C cementite 12. Consider the Fe-C phase diagram. An alloy that is 0.25% C by weight is slowly cooled from 1100oC to 750oC. Which of the following best describes the result a. A 2-phase mixture of ferrite (0.02% C) and austenite (0.63% C) b. A 2-phase mixture of ferrite (0.02% C) and Fe3C cementite (6.70% C) c. A 2-phase mixture of ferrite (0.63% C) and austenite (0.02% C) d. A single phase of austenite 13. Consider the Fe-C phase diagram. An alloy that is 0.25% C by weight is slowly cooled from 1100oC to 700oC. What are the relative amounts of each fraction a. About 97% ferrite and 3% Fe3C cementite b. About 3% ferrite and 97% Fe3C cementite c. About 69% ferrite and 31% Fe3C cementite d. About 31% ferrite and 69% Fe3C cementite 14. The copper-silver (Cu-Ag) phase diagram is shown below. What are the approximate relative proportions of the and phases at the eutectic point a. 9% and 91% b. 23% and 77% c. 92% and 8% d. 0% and 100% 15. Using the figure in the question above, what is the highest amount of silver that can form a single phase solid solution in copper at any temperature a. 91% b. 72% c. 8% d. Silver does not form a solid solution in copper 16. Using the Lever rule with a lead-tin alloy (see short answer questions for phase diagram) it is possible to determine the relative proportions of each phase at a particular temperature and composition. For a lead-tin alloy with 30% tin, what is the change in the proportion of the liquid phase upon cooling from 250oC to 200oC a. Decreases by approximately 45% b. Increases by approximately 45% c. Decreases by approximately 20% d. Increases by approximately 20% 200 300 400 500 600 700 800 900 1000 1100 1200 0 10 20 30 40 50 60 70 80 90 100 Composition (wt % Ag) T e m p e ra tu re ( oC ) + L + L + L 17. Using the time-temperature-transformation (TTT) curve for Fe/C, predict what will be formed if a steel at 800oC is rapidly cooled to 450oC, held for 10 seconds, then rapidly cooled to room temperature. a. 50% bainite, 50% martensite b. 75% bainite, 25% pearlite c. 75% pearlite, 25% martensite d. 100% bainite 18. A eutectoid iron-carbon alloy is cooled rapidly to 450oC, held for 100 seconds then quenched to room temperature. Determine the final product using the TTT curve. a. About 50% bainite, 50% austenite b. About 50% bainite, 50% martensite c. 100% bainite d. 100% martensite 19. Which of the following is true about ceramics whose bonding is predominantly ionic a. Negatively and positively charged ions are arranged in straight chains, branched chains or crosslinked chains that are held together by electrostatic interactions b. They have close-packed structures with many nearest neighbours, due to their internal structure of positive ion cores surrounded by a ‘cloud’ of negative ions that move relatively freely through the lattice. c. They have structures that are determined by the relative ratios of the radii of the negatively and positively charged ions. The optimum structure surrounds each + ion with as many – ions as possible with the – ions not quite touching each other. d. They have structures lacking order. Ions are packed together in random arrangement. Time (s) 10 102 103 104 105 1 200 400 600 800 T ( °C ) 0 Austenite ( ) Pearlite ( + Fe3C) Bainite ( + Fe3C) 0% 50% 90% Martensite Austenite ( ) 0% 50% 100% 20. Caesium bromide (chemical formula CsBr) is an ionic ceramic material. The radii of Cs+ and Br- are 0.170 and 0.196 nanometres (10-9 metres) respectively. Using the data in the table below, which of the following is the likely crystal structure for caesium bromide rc/ra Coordination number < 0.155 2 0.155-0.225 3 0.225-0.414 4 0.414-0.732 6 0.732-1.0 8 > 1.0 12 a. (coordination number = 6) b. (coordination number = 3) c. (coordination number = 8) d. (coordination number = 4) + _ _ _ _ – – – – + – – – – _ + _ _ + – + + – + + – + – + – + – + + + – + – – + + – – – – 21. What is the benefit of using a fibre-reinforced composite a. The fibres tangle and are held together by van der Waal’s forces, increasing the load needed to pull them apart, thereby strengthening the composite b. The matrix is stronger and takes a larger proportion of the load, but the fibre helps to hold the matrix together, preventing cracks from forming and propagating c. Fibre is often cheap and so reduces the volume required of the expensive matrix material d. The fibres are stronger and take a large proportion of the load. They are often brittle, but the ductile matrix prevents crack propagation 22. A glass-fibre-reinforced polymer matrix composite panel is to be made with maximum strengthening and stiffening possible along a particular direction in the plane. A first attempt has long fibres in the form of a flat mat, in which they twist around and through each other in random arrangement in the plane. When tested, there is improvement over tensile strength of the polymer alone, but not so much as desired. Which of the following possibilities offers the best prospects of improvement a. Make it with long fibres aligned perpendicular to the direction of desired maximum strengthening and stiffening. b. Use short length fibres as these are more effective in strengthening and stiffening than long lengths. Align them along the direction of desired maximum strengthening and stiffening. c. Make the glass fibre diameter much larger (i.e. rods rather than fibres). This will increase the volume fraction of the stronger, stiffer component. d. Make it with long fibres, aligned along the direction of desired maximum stiffening and strengthening. 23. Which of the following is not a recognised method of preventing rebar corrosion a. Avoid using chlorides b. Use less dense concrete c. Lower the W/C ratio d. Ensure a proper cover (at least 5 centimetres) 24. Concrete of bulk density 2400 kg/m3 has a water/cement ratio of 0.38 and an aggregate/cement ratio of 5.8. How much aggregate is needed for 2000 kg of the concrete a. 1616 kg b. 1655 kg c. 1706 kg d. 1939 kg 25. The specific gravity, Gs, of an aggregate is 2.59. Its bulk dry density (saturated surface dry conditions) is 1500 kg/m3. What volume of mortar must be added to completely fill the void space in 20 m3 of the aggregate Assume the density of water is 1000 kg/m3. a. 0.42 m3 b. 8.42 m3 c. 7.72 m3 d. 6.92 m3 26. If when cement is hydrating the relative humidity around the cement becomes less than about 80% what will happen a. Nothing b. Bleeding is prevented, giving strong, uniform concrete c. The lack of water will mean temperatures will increase greatly due to the hydration reactions, causing further drying and cracking d. Reactions will cease and there will be little extra gain in strength 27. The following graph shows the heat generated upon curing of concrete at three different temperatures. Arrange these curves in order of temperature, from lowest to highest. a. 1 < 2 < 3 b. 2 < 3 < 1 c. 3 < 1 < 2 d. 3 < 2 < 1 28. What are the typical proportions of the constituents in concrete a. 65-75% cement paste, 10% air voids and the remainder are aggregates b. 15-25% cement paste, 10% air voids and the remainder are aggregates c. 70-80% cement paste with the remainder taken up by aggregates d. 20-30% cement paste with the remainder taken up by aggregates 29. Which of the following does NOT contribute towards creep in concrete a. Internal seepage of water b. Presence of voids c. Presence of reinforcement bars d. (Visco-)elastic extension of paste or aggregate 30. What are the main phenomena that occur during cement hydration a. Reactions between cement and water - calcium aluminate and aluminoferrite react rapidly and calcium silicates react more slowly. Major products are calcium aluminate hydrate gel and calcium hydroxide. b. Reactions between cement and water - calcium silicates react rapidly and calcium aluminate and aluminoferrite react more slowly. Major products are calcium silicate hydrate gel and calcium hydroxide. c. Reactions between cement and water - calcium aluminate and aluminoferrite react rapidly and calcium silicates react more slowly. Major products are calcium silicate hydrate gel and calcium hydroxide. d. Reactions between cement and water - calcium aluminate and aluminoferrite react rapidly and calcium silicates more slowly. Major products are calcium silicates and calcium hydroxide. 31. Identify which of the following statements is NOT correct. The slump of a concrete mix is increased by use of: a. High cement paste content b. An aggregate with a large particle size c. An angular aggregate d. Use of a plasticiser 32. The details of a standard concrete mix are as follows: A/C % sand W/C 4.5 35 0.45 What is the density of the concrete if the water content is 187.6kg/m3 a. 2120 b. 2480 c. 2560 d. 2710 H e a t g e n e ra te d Time 3 2 1 33. What is the effect of moisture on curing concrete, and why a. Increasing the time exposed to moisture leads to increased setting time because it causes the hydration reactions to take longer b. Increasing the time exposed to moisture leads to decreasing strength because oxygen cannot easily get into the cement to help hydration reactions occur c. Increasing the time exposed to moisture leads to increasing strength because water is required to cause hydration reactions and subsequent setting of cement d. Increasing the time exposed to moisture leads to decreased setting time because it is easier for the hydration reactions to take place if there’s water present 34. Which of the following is NOT one of the components of Hardened cement paste (HCP) a. Unhydrated cement b. Calcium Silicate Hydrate c. Tricalcium Aluminate d. Crystals of Calcium Hydroxide 35. Typically, what percentage of concrete may be taken up by admixtures a. 1-2% by weight of cement b. 5-9% by weight of cement c. 10-15% by weight of cement d. 20-25% by weight of cement 36. Which of the following is NOT a reason for adding air entraining agents to a mortar a. Adding air entraining agents to a mortar reduces its porosity and therefore increases its strength b. Air entraining agents modify the mortar’s pore structure making it more durable. c. Adding air entraining agents to a mortar increases its stability d. Adding air entraining agents to a mortar increases its water retention 37. Which of the following describes creep deformation in concrete a. Initial elastic strain on the application of load followed by a gradual increase in reversible strain over a considerable period of time under load b. Initial elastic strain on the application of load followed by a gradual increase in semi- irreversible strain over a considerable period of time under load. c. Initial elastic strain on the application of load followed by a sharp increase in semi- irreversible strain over a very short period of time under load d. Initial elastic strain on the application of load followed by a sharp increase in reversible strain over a very short period of time under load 38. A 1:1:6 Mortar mix (by volume) has a W/C ratio of 1.20(by mass). The bulk density and relative density of the constituents are as follows: OPC Lime Sand Bulk Density (kg/m3) 1400 570 1650 Relative Density 3.15 2.26 2.65 How much (m3) mortar is produced with 25 kg of OPC a. 0.0225 m3 b. 0.1092 m3 c. 0.2169 m3 d. 0.4521 m3 39. You have designed a concrete mix to be poured into a heavily reinforced section on site. Once you have made your mix you perform a slump test. What slump should you aim for to ensure you are able to place your concrete a. 0 mm b. 50 mm c. 70 mm d. 120 mm 40. It is desired to select a material to form a component for a structural aircraft element. If one of the design objectives is for the component to be as lightweight as possible, whilst the constraints are that the component must remain elastic up to a particular value of stress and also have a minimum stiffness specified by the designers. Which of the following describes the material properties that should be used in the material selection process a. Density, Young’s Modulus, yield strength b. Density, cost per unit mass, Young’s modulus, yield strength c. Cost per unit mass, yield strength, Young’s modulus d. Tensile strength, density, yield strength 41. What role does a contracting engineer play in construction a. They are usually the lead designer for building construction b. They are usually the lead designer for civil engineering projects c. They are primarily responsible for the actual construction phase of a project d. They are primarily responsible for overall management of complex projects 42. What is ‘tendering’ a. A part of the design process where designs are interpreted by the construction team into a plan for construction. b. A process where contracting engineers bid to carry out construction work, pricing their costs based on information provided by designers and the client. c. The initial design stage, where a consultant comes up with a variety of solutions to the client’s needs. d. The end of the construction project, where the construction is commissioned and handed over to the client. 43. Which of the following describes the terms ‘formwork’ and ‘falsework’ a. Formwork is the ‘mould’ for concrete, the barriers which hold the fluid concrete in place until it has set. Falsework is the framework of (usually) steel or timber which holds the formwork securely in place. b. Formwork is the framework of (usually) steel or timber which holds the formwork securely in place. Falsework is the ‘mould’ for concrete, the barriers which hold the fluid concrete in place until it has set. c. Formwork is the frame of reinforcing steel that is to be placed within the concrete, whilst falsework is the temporary material that surrounds the planned concrete pour creating a mould in which the concrete will set. d. Formwork is the temporary material that surrounds the planned concrete pour creating a mould in which the concrete will set, whilst falsework is the frame of reinforcing steel that is to be placed within the concrete. 44. Why are I-beams used rather than a solid beam of rectangular cross section of similar mass a. Because I-beams are formed from flat sheets of steel welded together they are easier to produce, and therefore cheaper and more convenient. b. Although there is no structural difference in performance between these two options, the use of an I-beam is more convenient because its form allows other structural elements to be connected to it more easily. c. In bending, the sections of the beam away from the upper and lower edges limit deflections, preventing the beam from bending and properly taking the applied loads. It is necessary to use an I-beam to allow sufficient bending to occur for the loads to be properly supported. d. Resistance to bending in a beam is primarily provided by the regions near the top and bottom of the beam. Other areas contribute relatively little to structural performance, so an I- beam simply provides this material with little else. 45. Why are more traditional lattice truss structures now less used for open plan, low rise structures than portal frames a. They are far more challenging to construct and even though the lattice truss can span larger distances, its complexity limits its popularity. b. They are unable to span as large a distance, and are inefficient in their use of roof space, creating a large, unusable volume in the structure. c. The greater complexity of the structure and requirement for multiple connections between the lattice components means there is much more chance of failure of the structure. d. They cannot be built as tall as portal frames, which for modern industrial and retail facilities is not as useful. 46. What makes pad foundations and strip foundations different a. Pad foundations are isolated from one another and used to support columns whereas strip foundations are used to support walls. Only strip foundations may be reinforced. Pads may be combined with ground beams to link them together. b. Pad foundations are isolated from one another and used to support columns whereas strip foundations are used to support walls. Only strip foundations may be reinforced, and can be combined with ground beams to link them together. c. Pad foundations are isolated from one another and used to support columns whereas strip foundations are used to support walls. They may both be reinforced or unreinforced. Pads may be combined with ground beams to link them together. d. Pad foundations are isolated from one another and used to support columns whereas strip foundations are used to support walls. Only pad foundations may be reinforced, and can be combined with ground beams to link them together. 47. In a flexible pavement for a highway, what is the subgrade a. A mix of bitumen and relatively fine aggregate used as part of the upper surface of the road b. A dense bitumen / aggregate mix that is used to withstand and distribute wheel loads c. Well-graded aggregate that provides the artificial foundation for the road d. Soil or rock that provides the natural foundation for the road 48. The table below gives K values that may be used in the formula ( = | |) used to determine the length of vertical crest or sag curves on a highway. The gradient as a road approaches a vertical curve (p) is -1% and the gradient leaving the curve (q) is +2%, whilst the absolute minimum curve length is 39 metres. What should the speed limit be Design speed (km/hr) 120 100 85 70 60 50 Desirable minimum K value – crest curves 182 100 55 30 17 10 Absolute minimum K value – crest curves 100 55 30 17 10 6.5 Absolute minimum K value – sag curves 37 26 20 20 13 9 a. 120 km/hr b. 85 km/hr c. 60 km/hr d. 50 km/hr 49. What is a backdrop connection a. A robust vertical pipe arrangement that allows incoming flow to a manhole to be rapidly dropped in height, allowing incoming pipes to be at a shallower gradient. b. The connection between a rainwater pipe on a structure and the main surface water sewer. c. It is the arrangement in a road gulley whereby the water flows to the base of the gulley pot before rising up a connecting pipe to the main drainage pipe. This helps prevent sediment and other debris getting into the main sewer. d. The connection between two sections of pipe that allows a bend in the pipe. Short answer questions: 1. A hypothetical metal has a unit cell structure known as simple cubic (see figure) which contains 8 corner atoms touching along the sides of the cube (similar to BCC without the central atom). What is the atomic packing factor (APF) for this structure 2. The atomic symbol of an isotope of Cadmium is Cd 95 48 . How many neutrons does each atom of this isotope contain 3. Ions are very important in many situations. How and why do they form 4. Give two definitions of the yield stress of a steel from a stress-strain curve. 5. The figure below shows a force applied to a surface on an object. State the type of stress applied and calculate its magnitude. 6. Consider the Fe-C phase diagram. An alloy that is 2.00% C by weight is slowly cooled to 1200oC. What phases and compositions will result 7. Consider the Fe-C phase diagram. An alloy that is 1.50% C by weight is slowly cooled from 1600oC. Over what temperature range does solidification occur 8. Consider the Fe-C phase diagram. An alloy that is 0.25% C by weight is slowly cooled from 1100oC to 700oC. What are the compositions of the phases formed 2370 N 0.134 m 0.175 m 9. The lead-tin (Pb-Sn) phase diagram (below) contains three phases, , and liquid (L) is shown below. What is the melting point of pure tin 10. A eutectoid iron-carbon alloy is cooled rapidly to 400oC, held for 1000 seconds then quenched to room temperature. Determine the final product using the TTT curve given earlier. 11. Ceramics are bonded by one of two basic bonding types, or a hybrid of the two bonding types. Which two bonding types are involved 12. What are the two major constituents of hardened cement paste 13. A concrete pour is to take place outside on a UK site (average temperature 12oC). The concrete has to reach a particular design strength before further work can take place. Cube samples of an identical concrete mix are found to obtain this design strength after 2.5 days in laboratory conditions (22oC). Assuming strength and maturity are linearly related, how long will it be until this further work on the site can take place 14. Concrete cubes cured at 20oC for 7 days resulted in a characteristic strength fc of 38.1 N/mm2. Given that the maturity of concrete can be quantified as t(T+10) oChr, what would the fc be if the curing details over the 7 days were 2 days at 6oC, 4 days at 8oC and 1 day at 10oC 15. How is the chemical 3CaO.SiO2 represented in cement chemistry notation 16. What does mortar consist of 17. What is the main disadvantage in using partial cement replacement materials 18. A batch of concrete cubes are cured at 21oC for 15 days, giving a characteristic strength fc of 35 N/mm2 (concrete maturity can be quantified as t(T+10) oChr). If a second batch of cubes are accidentally cured at 16oC for the first 4 days, for how many days should they be cured at 28oC if they are required to they reach the same strength as the first batch of cubes 19. What are the main tests performed to define the properties of fresh mortar 20. The grading of a concrete sand is given in the table. What is the fineness modulus of the sand Sieve size (mm) Weight retained (g) % retained Cumulative % passing Cumulative % retained 10 0.0 0.0 100.0 0.0 5 2.0 2.0 98.0 2.0 2 15.5 15.5 82.5 17.5 1.18 18.1 18.1 64.5 35.5 0.6 31.6 31.6 32.9 67.1 0.3 16.0 16.0 16.9 83.1 0.15 7.2 7.2 9.7 90.3 <0.15 8.9 8.9 - - 0 50 100 150 200 250 300 350 400 0 10 20 30 40 50 60 70 80 90 100 Composition (wt % Sn) T e m p e ra tu re ( oC ) + L + L + L 21. A batch of concrete cubes were cured in an oven at 30°C for 7 days, resulting in a characteristic strength fc of 35 N/mm2 (concrete maturity can be quantified as t(T+10) °Chr). A second batch of cubes were also cured in an oven at 30°C for 3 days, at which point the oven broke and the temperature fell to 15 °C for the remaining 4 days of the curing period. What is the resulting characteristic strength of the second batch of cubes 22. Determine the weight of the wet filter paper using the following data. Mix ratios by mass: Cement Lime Sand Water 1 0.4 6.9 1.2 Bulk Density of Mortar = 2120kg/m3 Volume of mould filled with mortar = 75ml Dry filter paper = 3.54 g Water retentivity in mortar = 91.3% 23. 125 grams of dry cement powder is added to 1 litre of water. If the specific gravity of the powder is 3.125 how much water will the cement powder displace (Density of water = 1 g/cm3) 24. A material index has been identified as E1/3/ . By drawing lines on the below chart which link equal values of this index [HINT – join two points where the material index = 10, then draw parallel lines], determine whether bamboo, brick, silicon carbide or a titanium (Ti) alloy would be the best material to use. 25. Briefly explain how the process of slipforming is carried out. 26. Describe two ways in which a multi-storey steel-framed building might be structurally braced against wind loading. 27. Briefly describe ways in which drainage occurs from rural highways. 0.001 0.01 0.1 1 10 100 1000 0.1 1 10 100 Yo u n g' s M o d u lu s (G P a) Density (Mg/m^3) Metals Zn alloys Pb alloys Tungsten carbide Ni alloys Cu alloys Steels Cast irons Ti alloys Al alloysMg alloys Technical ceramicsAluminium nitride Silicon nitride Silicon carbide Silicon Boron carbide Alumina Glasses Al SiC GFRP CFRP Composites Porous ceramics Brick Concrete Stone Natural materials Leather Wood (across grain) Cork Wood (along grain) Bamboo Polymer foams Flexible polymer foams Rigid polymer foams Polymers Elastomers Thermoplastics Thermosets 28. A cube, shown below, is subjected to an isostatic compressive stress (i.e. the same stress in all directions), S. If the Young’s modulus is E and the Poisson’s ratio is , determine an expression for the strain in the x-direction. The sign convention is that tension is positive. Show your working. 29. A component is subjected to a load and the resulting stress-strain curve is plotted below. After following this curve, the load is then reduced to zero. Calculate the permanent plastic strain at this point, showing your working. 30. Describe the atomic structure (i.e. number of protons, neutrons and electrons) of caesium (chemical symbol Cs). z x y S S S S S S 31. The figure below shows an engineering stress-strain curve for a specimen of brass. Give values for the yield stress, tensile strength and Young’s Modulus for this material, showing calculations where necessary. 32. The details of a standard concrete mix are as follows: What are the cement and fine aggregate contents in kg/m3 A/C % sand W/C Density 4.5 35 0.45 2430 kg/m3 33. Determine, showing your working, the electronic structure of a calcium (Ca) atom. 0 50 100 150 200 250 300 350 400 450 500 0 0.1 0.2 0.3 0.4 St re ss ( M Pa ) Strain 1. Answers Multiple choice questions: 1. c 2. d 3. c 4. d 5. a 6. a 7. d 8. d 9. a 10. d 11. b 12. a 13. a 14. b 15. c 16. a 17. a 18. c 19. c 20. c 21. d 22. d 23. b 24. a 25. b 26. d 27. d 28. d 29. c 30. c 31. c 32. b 33. c 34. c 35. a 36. a 37. b 38. b 39. d 40. a 41. c 42. b 43. a 44. d 45. b 46. c 47. d 48. c 49. a Short answer questions: 1. 0.52 2. 47 3. Ions form because atoms are more stable with certain configurations of electrons in their surrounding orbitals and shells. They lose or gain electrons to attain these stable states. 4. (i) The stress required to produce noticeable plastic deformation (ii) The stress at the proportional limit, where the curve deviates from linear behaviour (iii) The stress required to give a small permanent plastic strain (e.g. 0.001 or 0.002). 5. Shear stress with magnitude 101.1 kPa 6. A 2-phase mixture of austenite (1.85% C) and liquid (3.85% C). 7. It will start to solidify at about 1420oC and finish solidifying at about 1260oC 8. ferrite is 0.02% C and Fe3C cementite is 6.70% C. 9. Approximately 232oC. 10. 100% Bainite. 11. Ionic and covalent (electrons either transfer totally from metal to non-metal or are shared between neighbouring pairs of atoms). 12. Calcium silicate hydrate and calcium hydroxide. 13. 3.6 days. 14. 22.5 N/mm2. 15. C3S 16. Cement powder, water, fine aggregate. 17. They lead to lower strength gains in the concrete. 18. 9.5 days. 19. Consistency and retentivity 20. 2.96. 21. 5.29 g. 22. 40 ml. 23. 27.5 N/mm2. 24. Bamboo 25. As provided in notes 26. Points could include moment resistance at joints, cross-bracing, RC walls or slabs, RC core to building 27. Issues could include: cutting or embankment; road run-off; drainage directly into soil; coarse-grained drains; concrete drainage channels. 28. = 1 ( + + ) = (2 1) 29. Young’s modulus is approximately 100 / 0.003 = 33.3 GPa. At maximum point, stress = 200 MPa and strain = 0.009. On unloading, the strain recovery will be 200/(33