Читать книгу Materials for Biomedical Engineering - Mohamed N. Rahaman - Страница 159

1 4.1 The figure below shows general stress–strain curves for different types of materials at room temperature:Which curve best represents the mechanical response of (i) alumina, (ii) high density polyethylene, (iii) polystyrene, (iv) stainless steel, and (v) titanium.Which curve represents the toughest material?Which curve represents the material with the lowest Young’s modulus?Explain your answers.

2 4.2 A cylindrical specimen of length 100 mm and diameter 10 mm is loaded in tension in a mechanical testing machine. Upon application of a force of 1000 N, the length increased to 100.5 mm. Determine the engineering (nominal) stress and strain in the specimen. If all the deformation occurred within the elastic region of its mechanical response, determine the Young’s modulus of the material.

3 4.3 Determine the stress on the femoral bone of average diameter 2.5 cm in a human when it is subjected to a compressive force equal to the weight of a human of mass 90 kg (~200 pounds). How does this stress compare with the tensile strength of human cortical bone?

4 4.4 The following data were obtained in tensile testing of an aluminum alloy specimen of gage length 50.8 mm and diameter 12.8 mm:Force (kN)Length (mm)050.808.950.8517.850.9035.651.0044.551.0553.451.1657.851.3162.352.0771.253.369.4 (fracture)54.2Plot the engineering stress–strain curveDetermine the Young’s modulus, yield strength (at an offset strain 0.2%), and the ultimate tensile strengthDetermine the engineering fracture strength and the true fracture strength, given that the diameter of the fractured specimen was 10.16 mm.

5 4.5 Define toughness and resilience. Draw a stress–strain curve for a ductile material and indicate how the toughness and resilience can be determined from it.

6 4.6 Explain why and how grain size influences the strength of metals. Give a relationship (name and equation) between strength and grain size, and define the terms in the equation.

7 4.7 Explain why a metal that has undergone mechanical fatigue often fails at stresses far smaller than those for a similar metal that has not. Is the fracture of a fatigued metal expected to be ductile or brittle in character?

8 4.8 Explain why a ceramic material such as Al2O3 commonly shows a compressive strength that is far higher than its flexural strength.

9 4.9 Discuss the most important properties that should be considered in designing metals, ceramics, and polymers for use as biomaterials in load‐bearing applications in vivo.

10 4.10 Explain the differences between diamagnetism, paramagnetism, ferromagnetism, and ferrimagnetism, and how these differences influence the applications of biomaterials.

11 4.11 Distinguish between phonons and photons. Explain how phonons influence the thermal conductivity of materials.

12 4.12 Metals typically have high electrical and thermal conductivities. On the other hand, diamond has a high thermal conductivity but is an electrical insulator. Explain.

13 4.13 Determine the number of unpaired electrons in the following atoms or ions: Cr, Al3+, Zn, Ni, O2−, Co2+.

14 4.14 Assuming that the magnetization of nickel results from its unpaired electrons only, calculate the saturation magnetization per kilogram of nickel which has a density of 8.9 g/cm3 and an FCC structure of unit cell length 0.352 nm.