东北大学工程材料

工程材料作业

1 The Structure of Metals

REVIEW QUESTIONS

1.1Explain the difference between a unit cell and a single crystal.

The smallest group of atoms showing the characteristic lattice structure of a particular metal is known as a unit cell.It is the building block of a crystal, and a single crystal can have many unit cells.（包含与被包含关系）

1.2In tables on crystal structures. Iron is listed as having both a bcc and a fcc

structure, why?

Each sphere in these illustrations represents an atom.（只代表一个原子，而非铁物质）

1.3Define anisotropy. What materials can you think of other than metals that

exhibit anisotropy behavior?

Because the b/a ratio is different for different directions within the crystal, a single crystal has different properties when tested in different directions. We say that a single crystal is anisotropic.（定义）

A common example of anisotropy is woven cloth, which stretches differently when we pull it in different directions, or plywood, which is much stronger in the planar direction than along its thickness direction (it splits easily).

1.4What effects does recrystallization（再结晶）have on properties of metals?

提高了滑移的韧度，降低了强度，提高了金属的塑性

1.5What is strain hardening, and what effects does it have on the properties of

metals?

1.6 Explain what is meant by structure-sensitive and structure insensitive properties of metals.

1.7 Make a list of each of the ini\jor kinds of imperfection in the crystal struct~~oret' metals. and describe them.

1.8 What influence does grain size have on the mechanical properties of metals'?

1.9 What is the relationship between the nucleation rate and the number of grains

per unit volume of a metal?

1.10 What is a slip system, and what is its significance?

1.11 Explain the difference between recovery and recrystallization.

1.12 What is hot shortness, and what is its significance?

1.13 Explain the differences between cold-, warm-, and hot-working of metals.

1.14 Describe what the orange peel effect is.

1.15 Why can't some metals such as lead become stronger when cold worked?

1.16 Describe the difference between preferred orientation and mechanical fibering.

1.17 In microscopy, it is common practice to apply a chemical etchant to a metal in order to highlight grain boundaries and microstructures. Explain why.

1.18 What is twinning'? How does it differ from slip?

It’s a plastic deformation in which a portion of the crystal forms a mirror image of itself across the plane of twinning. Twins form abruptly and are the cause of the creaking sound ("tin cry") that occurs when a tin or zinc rod is bent at room temperature. Twinning usually occurs in hcp metals.

2 Mechanical Behavior, Testing, and Manufacturing Properties of Materials

REVIEW QUESTIONS

2.1 Distinguish between engineering stress and true stress.

2.2 Describe the events that occur when a specimen undergoes a tension test. Sketch a plausible stress-strain curve, and identify all signiticant regions and points between them. Assume that loading continues up to fracture.

2.3 What is ductility, and how is it measured?

2.4 In the equation o = Ke", which represents the stress-strain curve for a material, what is the significance of the exponent n?

2.5 What is strain-rate sensitivity, and how is it measured?

2.6 What test can measure the properties of a material undergoing shear strain? 2.7 What testing procedures can be used to measure the properties of brittle materials, such as ceramics and carbides'!

2.8 Describe the differences between brittle and ductile fracture.

2.9 Explain the difference between stress relaxation and creep.

2.10 Describe the difference between elastic and plastic behavior.

2.11 Explain what uniform elongation is in tension testing.

2.12 Describe the difference between deformation rate and