MECH 341 Final, Fall 2010

FACULTY OF ENGINEERING & ARCHITECTURE AMERICAN UNIVERSITY OF BEIRUT MECH341 MATERIALS LAB FINAL EXAM, Fall 20010-11; January 28, 2011 Duration: One hour (60 minutes) CLOSED BOOK & NOTES Please sign and date this front sheet PRIOR to working on this test. I, the undersigned, and in the process of taking this test, pledge that I (1) will conduct myself in a professional manner (2) will not communicate with other examinees regarding the subject-matter of this test while this test is in session and will ONLY communicate with the teacher administering this test. (3) will use only what is handed to me with the exception of a calculator & pens (4) acknowledge that I am familiar with FEA’s “Rules and Regulations on Disciplinary Action” and understand that in case of policy violation, that I, myself, will be responsible for the consequences of my actions. STUDENT NAME ____________________________ STUDENT NUMBER ____________________________ STUDENT SIGNATURE ___________________________ DATE ___________________________ 1/15 You may use all, some, or none of the information contained in the following few pages. Tensile tests  Proportional Limit Stress pl = stress value at which the stress-strain curve goes nonlinear  Yield Point Stress, y = stress value at which the stress-strain curve goes horizontal  0.2%-Offset Yield Stress, y = the stress value at which a line drawn with slope E starting at 0.002 strain intersects the stress-strain curve  Stress = load / area =F/A0  Strain = deformation / gage length = L / Lo  Ultimate Tensile Stress, ult = largest stress on the stress-strain curve  Engineering Fracture Stress = fracture load / original area  True Stress = T = F/Ai  (1+  )  True Fracture Stress = fracture load / fracture area =Ff/Ai  True strain = T = ln (Li /L0) = ln(1+)  Modulus of Resilience, Ur = σy 2/2E  Percent Elongation = (Lf - Lo) / Lo x 100%  Percent Elongation of L" Gage Length = LG/ LG " x 100%  Percent Reduction in Area = (Af0 -AG0) / AG0 x 100% Flexure test 2/15 Hardness test P in kg D in mm d in mm TS (psi) = 500 x HB or TS (MPa) = 3.45 x HB Fatigue test 3/15 4/15 r/d Kf = 1+ (Kt -1)q where Kt is the theoretical or geometric factor and q is the notch sensitivity factor Metallographic test N = 2n-1 N is the number of grains (grains/in2) evaluated as the number of grains found in an image whose area is 1 in2 and magnification is 100x n is the ASTM grain number NM = the number of grains per square inch at magnification M, and n is the ASTM grain size number. Short beam flexure test Fsbs = 0.75 x (P/(b x h)) Fsbs = short-beam strength, (MPa) P = maximum load observed, (N) b = measured specimen width, (mm) h = measured specimen thickness, (mm) 5/15 Creep & Stress Relaxation of Polymers test σ =σ0[exp(-t/ τ )] ε=σ0/[E(1+t/ τ )] σ0: is applied stress. t: the elapsed time (s) τ: is the relaxation time, its is a time independent constant characteristic of material. E: material modulus of elasticity at time t=0. X-ray diffraction test The lattice parameter (unit cell edge length “a”) is identified as follows: For body centered cubic crystal structure For Face centered cubic crystal structure where R is the atomic radius Weibull distribution S is the rate of survival is the applied stress MPa QUESTIONS ARE GRADED EQUALLY; 6/15 No extra penalty for wrong answers so make sure you answer all questions. 1. What is the version of your question sheet? (this question is not graded). a) A Metal Testing Labs 2. On the tensile stress strain curve found below the stress level at which the stress- strain curve goes horizontal and highlighted by point “B” is defined as: A- Yield point B- Ultimate tensile strength C- Upper Yield point D- Proportionality limit stress E- none of the above 3. The Toughness, defined as: A- The area under the elastic portion of the load-deformation curve B- The area under the entire load-deformation curve C- A measure of a materials resistance to localized plastic deformations (scratch) D- The area under the entire stress-strain curve E- none of the above 4. The Hardnability, defined as: A- The ability of a metal to be hardened by heat treatment. B- The measure of a materials resistance to localized plastic deformations (scratch) C- The total energy absorbed by the specimen till fracture D- All of the above E- none of the above 5. An Iron material is to be used in steel structure construction, a specimen is taken for testing. If the specimen have yield stress of 360 MPA and a modulus of elasticity of 220 GPa what would be the modulus of resilience for the tested steel? 7/15 A- 0.589 J/m3 B- 5.89 J/m3 C- 0.29 J/m3 D- 208 MPa E- none of the above 6. A cast iron rod used as a specimen in tensile testing has a 12mm gage diameter, was loaded till fracture. The measured cross-sectional diameter at the point of fracture was 6mm . What is the % area reduction of the specimen? A- 41.3 B- 65.9 C- 82 .4 D- 75.0 E- none of the above 7. Which of the following does affects the accuracy of the test experiment? A- Test method B- Operator bias C- Apparatus calibration D- None of the above E- All of the above 8 A cylindrical steel rod having a modulus of elasticity of E=207 GPa and a yield strength of 310 MPa is subject to a load of 11100 N if the length of the rod is 200mm what would be the diameter of the specimen if elastic strain corresponding to the applied load is 0.00090? A- 15.70 mm B- 12.62 mm C- 4.35 mm D- 8.71 mm E- none of the above 9. The annealing is a heat treatment process in which a material is exposed to an elevated temperature for an extended time period then slowly cooled, in order to increase the material softness and ductility. A-TRUE B- FALSE 10. A cast iron rod used as a specimen in tensile testing has a 12 mm gage diameter and a 200mm initial length, was loaded till fracture. The measured cross-sectional diameter at the point of fracture was 8 mm and the measured length at the point of fracture is 250 mm . What is the % Percent Elongation of the specimen? A- 41% B- 35% C- 25% D- 33% E- none of the above 11. If a 212-cm copper wire having a 0.76 mm diameter. Starts to plastically deform under a load of 9.9 kg, find its yield strength. 8/15 A- 87 MPa B- 100 MPa C- 21.82 MPa D- 214 MPa E- none of the above 12. Which of the following is the stress strain curve for a highly brittle material? a b c A- Curve a B- Curve b C- Curve c D- All of the above E- None of the Above 13. A steel specimen having 25mm gage length and 7.4 mm cross-sectional diameter was tested under tensile loading. The Specimen elastic limit is encountered at 13000N load and 0.04 mm deformation. Identify the modulus of elasticity for the tested steel specimen? A- 231.5 GPa B- 500.5 GPa C- 1300.5 MPa D- 189 GPa E- none of the above 14. Consider the following three stresses versus strain plots of the plastic material generated at different strain rates Which of the following curves corresponds to specimen tested at the lowest strain rate? 9/15 A- Graph A B- Graph B C- Graph C D- none of the above 15. Which of the following is true: A- Increasing temperature decreases the impact toughness of steel B- Notching the specimen decreases the impact toughness of steel C- Increasing carbon content increases the impact toughness of steel D- All of the above E- none of the above 16. What does a higher ASTM number reflects: A- Higher ASTM Number reflects a larger grain size. B- Higher ASTM Number reflects a smaller grain size C- all of the above D- non of the above 17. The preparation of metallographic samples, involves typically a three-step process known as cut-polish-etch. The idea behind the etching step is to enhance the micro- structural features such as grain size and phase features by etching away the grain boundaries at a faster rate than that for the grains themselves. A- TRUE B- FALSE 18. For a ceramic material, the design criteria should be based on the a) 1), Fracture strength 2) Yield b) 1) Lower yield, 2) ultimate c) Weibull fracture stress model d) 1) Yield, 2) Ultimate strength e) None of the above 19. In the preparation of Metallographic steel Specimens etching is done by immersing the specimen in a special chemical solution for 45 seconds which of the following is the etchant used: A- Nital Etch B- Kroll’s reagent 10/15 a a . b c C- Kellers Etch D- All of the above E- None of the Above 20. A 100 ml Kroll’s reagent: composed of 98 ml ethyl alcohol and 2 ml - Nitric acid. A- TRUE B- FALSE A Brinell measurement on a carbon steel alloy using a 1500 Kg load and standard 10 mm ball indenter resulted in indentation 2.5 mm deep and 3.37 mm across. 21 Calculate the Brinell hardness value for this metal. A- 122 B- 80 C- 163 D- 200 E- None of the above 22. If the Brinel hardness value for that steel is 200 what is its carbon content A- 0.25 % B- 0.5 % C- 1.5 % D- 0.6 % E- None of the above A steel rod having a hardness of 160Bhn was subjected to a bending moment= 0.5 KN.m. The ultimate and yield strength are 1.2 and 1.0 GPa respectively. Given the following: d = 15mm, D/d = 1.01 , and r/d = 0.15, where D: large diameter, d: small diameter, r: notch radius. 23. For above bar determine the notch sensitivity factor “q ” A- 0.65 B- 0.75 C- 0.85 D- 0.80 E- None of the above 24. For the above bar, approximately determine the theoretical geometric fatigue stress concentration “Kt” at the notch: A- 1.8 B- 1.6 C- 1.3 D- 3.6 E- None of the above 25. For a specimen having the geometric fatigue stress concentration “Kt” is 1.4 and the notch sensitivity factor “q ” to be 0.65 identify the stress concentration Kf A- 0.65 B- 1.26 11/15 C- 1.56 D- 1.65 E- None of the above A three-point bending test is performed on a glass specimen having a rectangular cross section of height of 5 mm and width of 10 mm. the span length between the support pins is 50 mm. 26. If the proportional limit Force of the specimen above is measured at 2000 N at a deformation of 0.26 mm, calculate the Bending strain of that specimen at the proportionality limit point. A- 0.00312 mm/mm B- 0.01312 mm/mm C- 0. 31200 mm/mm D- 1.233mm/mm E- none of the above Polymer Testing Labs 27 The following are typical stress strain behavior encounters in polymeric material. Which of the following best describes Curve “c”. A- Curve ”c” is similar to that found for many metallic materials where the initial elastic deformation is followed by yielding and a region of plastic deformation B- Curve “c” illustrates the stress strain curve for a brittle material which fracture while deforming elastically C- Curve “c” is encounters for rubber like polymers, the deformation is totally elastic D- all of the above E- none of the above 28. Which of the following represents the strain vs. time response of a perfectly viscous material in response to a step load? 12/15 A- C- B- D-Non of the Above 29. Mechanical properties of polymers are sensitive to operating strain rate. Increasing the strain rate initiates: A- Increase in the elastic modulus. B- Reduction in tensile strength C- Enhancement of ductility D- None of the above E- All of the above Ceramic Testing Lab 30. In the Bend (Flexure) Test for Ceramic Material, specimens where subject to bending stress under the action of the three points loading grips. Identify the dominant failure mode encountered in the brittle ceramic specimens A- Interlaminar Shear Fracture B- Flexure Compression Fracture C- Inelastic Deformation. D- Flexure Tension Fracture E- All of the above. 31. Ceramics material is a a- Good conductor of electricity b- Ductile material c- Good thermal insulator d- None of the above e- all of the above 13/15 Composite materials Testing Lab: 32. In the short beam strength TEST for composite materials, the specimen fractures in instantaneously similar to metal fracture a- TRUE B- FALSE 33. In the short beam strength TEST for composite materials, the sketches shown are indicative for a a- Flexure compression fracture b- Flexure tensile fracture c- Inelastic deformation d- Interlaminar shear fracture e- None of the above A three-point short beam bending test is performed on a composite specimen having a rectangular cross section of 11 mm thickness and width of 23 mm. the span length between the support pins is 35 mm. 34. if short beam strength of that specimen is 30 MPa what would be maximum load recorded to fracture the specimen: A- 10120 N B- 5000 N C- 13493 N D- 1000 N E-none of the Above Cyclic Fatigue Lab 35. A Specimen is subject to a repetitive sinusoidal cyclic load varying between & identify the stress ratio for that cyclic load: A- -0.5 B- 0.5 C- -1 D- 2 E- None of the above 36. What is the type of stress that is shown below: 14/15 : A. Completely reversed stress cycle of sinusoidal form. B. Repeated stress cycle of sinusoidal form. C. Complicated stress cycle which might be encountered in a part such as an aircraft wing D. all of the above E. none of the above 37- The basic method for presenting engineering fatigue data is by means of________ A- S-N curves where the number of cycles is plotted against to failure stress B- S-N curves where stress is plotted against the number of cycles to failure C- None of the above 38- What is the effect of material hardness on the material geometric factor Kt? A- Kt decreases as the material hardness increases. B- Kt increases as the material hardness increases. C- Hardness has no effect on the material geometric factor Kt D- all of the above. X-Ray Diffraction Lab: 39. The interplanar spacing for a (310) set of planes in a Cromium BCC structure having lattice parameter a= 2.884 Ao is , a. 1.8505 Ao b. 1.0134 Ao c. 2.0393 Ao d. 0.9120 Ao e. none of the above 40. For The same Cromium sample identified above, estimate the atomic radius. a. 1.5868 Ao b. 2.5088 Ao c. 1.2488 Ao d. 4.5066 Ao e. none of the above 41. For a Material having an FCC crystal structure all planes having the sum of the miller indices (h+k+l) equal to an even number satisfies Braggs law and are detected using an X- RAY diffraction analysis A- TRUE B- FALSE 15/15