16 刚度 硬度 强度strength hardness stifness.docx

l 强度结构杆件所用材料在规定的荷载作用下，材料发生破坏时的应力称为强度。根据外力作用方式不同，材料的抗拉强度、抗压强度、抗剪强度等。Strength Definition: In materials science, the strength of a material is its ability to withstand an applied load without failure or plastic deformation.Material strength refers to the point on the engineeringstressstrain curve(yield stress) beyond which the material experiences deformations that will not be completely reversed upon removal of the loading and as a result the member will have a permanent deflection. The ultimate strength refers to the point on the engineering stressstrain curve corresponding to the stress that produces fracture.l 刚度刚度是指材料或结构在受力时抵抗弹性变形的能力。是材料或结构弹性变形难易程度的表征。在宏观弹性范围内，刚度是零件荷载与位移成正比的比例系数，即引起单位位移所需的力。一个结构的刚度（k）是指弹性体抵抗变形拉伸的能力。计算公式：k=P/P是作用于结构的恒力，是由于力而产生的形变。刚度的国际单位是牛顿每米（N/m）StiffnessDefinition: Stiffnessis the rigidity of an object the extent to which it resistsdeformationin response to an appliedforceThe stiffness,k, of a body is a measure of the resistance offered by an elastic body to deformation. For an elastic body with a singledegree of freedom(DOF) (for example, stretching or compression of a rod), the stiffness is defined aswhere, Fis the force applied on the body， is thedisplacementproduced by the force along the same degree of freedom (for instance, the change in length of a stretched spring)In theInternational System of Units, stiffness is typically measured innewtonsper meter. In Imperial units, stiffness is typically measured inpounds (lbs) per inch.l 弹性模量一般地讲，对弹性体施加一个外界作用，弹性体会发生形状的改变（称为“应变”），“弹性模量”的一般定义是：应力除以应变。杨氏模量（Youngs modulus），又称拉伸模量（tensile modulus）是弹性模量（elastic modulus or modulus of elasticity）中最常见的一种。公式记为E = / 其中，E 表示杨氏模数， 表示正向应力， 表示正向应变。杨氏模量Themodulus of elasticityDefinition: Themodulus of elasticity(also known as theelastic modulus, thetensile modulus, orYoungs modulus) is a number that measures an object or substances resistance to being deformed elastically (i.e., non-permanently) when aforceis applied to it. The elastic modulus of an object is defined as theslopeof itsstressstrain curvein the elastic deformation region:1A stiffer material will have a higher elastic modulus. An elastic modulus has the formWhere,stressis the force causing the deformation divided by the area to which the force is applied andstrainis the ratio of the change in some length parameter caused by the deformation to the original value of the length parameter. If stress is measured inpascals, then since strain is a dimensionless quantity, the units ofwill be pascals as well.l 刚度与弹性模量区别一般来说，刚度和弹性模量是不一样的。弹性模量是物质组分的性质；而刚度是结构的性质。也就是说，弹性模量是物质微观的性质，而刚度是物质宏观的性质。材料力学中，弹性模量与相应截面几何性质的乘积表示为各类刚度，如GI为扭转刚度，EI为弯曲刚度，EA为拉压刚度。Relationship to elasticityIn general,elastic modulusis not the same as stiffness. Elastic modulus is a property of the constituent material; stiffness is a property of a structure. That is, the modulus is anintensive propertyof the material; stiffness, on the other hand, is anextensive propertyof the solid body dependent on the materialandthe shape and boundary conditions. For example, for an element intensionorcompression, the axial stiffness isWhere, Ais thecross-sectional area,Eis the (tensile) elastic modulus (orYoungs modulus), Lis thelengthof the element.l 硬度硬度，物理学专业术语，材料局部抵抗硬物压入其表面的能力称为硬度。固体对外界物体入侵的局部抵抗能力，是比较各种材料软硬的指标。由于规定了不同的测试方法，所以有不同的硬度标准。各种硬度标准的力学含义不同，相互不能直接换算，但可通过试验加以对比。洛氏硬度这种硬度测定法是美国的SP洛克韦尔于1919年提出的，它基本上克服了布氏测定法的上述不足。洛氏硬度所采用的压头是锥角为120的金刚石圆锥或直径为1/16英寸（1英寸等于25.4毫米）的钢球，并用压痕深度作为标定硬度值的依据。测量时，总载荷分初载荷和主载荷（总载荷减去初载荷）两次施加，初载荷一般选用10千克力，加至总载荷后卸去主载荷，并以这时的压痕深度来衡量材料的硬度。洛氏硬度记为HR，所测数值写在HB后，洛氏硬度值计算公式为：式中h表示塑性变形压痕深度（毫米）；k是规定的常量；分母中的0.002（毫米）每洛氏硬度单位对应的压痕深度。对应于金刚石圆锥压头的k=0.20（毫米），对应钢球压头的k=0.26（毫米）。HardnessHardnessis a measure of how resistantsolidmatteris to various kinds of permanent shape change when a compressiveforceis applied. Some materials, such as metal, are harder than others. Macroscopic hardness is generally characterized by strongintermolecular bonds, but the behavior of solid materials under force is complex; therefore, there are