Mechanical properties of Materials
材料的机械特性
The materials properties can be classified into three major heading：（i） Physical，（ii） Chemical，（iii） Mechanical。
材料的特性可以分为三个重要的部分：1 是物理特性，2 是化学特性，3 是机械特性。 Physical Properties 物理特性
Density or specific gravity, moisture content, etc., can be classified under this category.
密度或者比重，水分含量等，都被分为这一类的范畴 Chemical Properties 化学特性
Many chemical properties come under this category. These include acidity or alkalinity,
许多化学特性都归入到这个范畴。这些特性包括酸性或碱性 reactivity and corrosion. The most important of these is corrosion which 反应性和腐蚀性。
can be explained in layman’s terms as the resistance of the material to decay while in continuous use in a particular atmosphere
这些中最重要的是耐腐蚀性，它可以被解释为在外行人看来作为材料
在特定大气中长期使用时抵抗腐蚀的能力。 Mechanical Properties(机械特性)
Mechanical properties include the strength properties like tensile, compression, shear, torsion, impact, fatigue and creep.
机械特性包括拉伸，压缩，剪切，扭转，冲击，疲劳和蠕变等强度特性。
The tensile strength of a material is obtained by dividing the maximum load, which the specimen bears by the area of cross-section of the specimen.
材料的抗拉强度由试样承载的最大载荷除以试样的横截面积获得。
This is a curve plotted between the stress along the Y-axis(ordinate) and the strain along the X-axis(abscissa) in a tensile test.
这是一个在拉伸试验中沿着Y轴（纵坐标）的应力和沿着X轴（横坐标）的应变的关系曲线。
A material tends to change or changes its dimensions when it is loaded, depending upon the magnitude of the load.
当材料加载时尺寸的变化，取决于载荷大小的变化。
When the load is removed it can be seen that the deformation disappears.
当卸载时可以看见变形消失。
For many materials this occurs up to a certain value of the stress
called the elastic limitσe.
对于许多材料来说这种发生的应力极限值称为弹性极限。 This is depicted by the straight line relationship and a small deviation thereafter, in the stress-strain curve（Fig.3.1）.
在应力-应变曲线中，直线关系和随后小的偏移描述了这个（加载和卸载的过程）。
Within the elastic range, the limiting value of the stress up to which the stress and strain are proportional, is called the limit of proportionalityσp.
在弹性范围内，应力与应变的比例的极限值被称作比例极限。
In this region, the metal obeys Hooke’s law, which states that the stress is proportional to strain in the elastic range of loading (the material completely regains its original dimensions after the load is removed). 在这个区域中，金属服从胡克定律，阐述了在加载的弹性范围内应和应变成比例关系（材料卸载后能够恢复到原来的尺寸）。
In the actual plotting of the curve, the proportionality limit is obtained at a slightly lower value of the load than the elastic limit. 在曲线绘制中，载荷的比例极限值比弹性极限值稍低，