5.TensileTesting(拉伸试验).doc

Tensile Testing(拉伸试验) Tensile testing is one of the most widely used mechanical tests. A tensile test helps determining tensile properties such as tensile strength, yield point or yield strength, % elongation, % reduction in area and modulus of elasticity. Since mechanical properties are to some extent influenced by the size and shape of the test specimen, it is customary to use standardized specimen.The essential feature of a round (cylindrical) test specimen are the diameter D. parallel length PL, gauge length L., and end fillet radius r. These dimensions may be set as follows:Diameter 10mm D0Parallel length 55mm 5.5 D0Gauge length 50mm 5 D0End fillet radius 3mm r Tensile test is carried out by gripping the ends E, E of the specimen in a tensile testing machine and applying and increasing pull Fig. On to the specimen till it fractures.During the test, the tensile load as well as the elongation of a previously marked gauge length in the specimen is measured with the help of load dial of the machine and extensometer repectively. These readings help plotting stress-strain curve as shown in Fig.After fracture, the two pieces of the broken specimen are placed as if fixed tighter and the distance L between two gauge marks and the diameter D at the place of fracture are measured.The various tensile properties are calculated as follows: 1. Yield strength=Load at Yield point/A0i.e.(/4).D022. Ultimate tensile strength=Ultimate load, Pmax/A03. % Elongation=(L1-L0)/L01004. % Reduction in area=(A0-A1)/ A0 100 5. Youngs modulus of elasticity E Stress at any point within the=elastic limit.i.e. OA/Strain at that point or E=PL./A.LWhere P is load at any point up to the elastic limit L. is the gauge length A. is original area, and L is the elongation of change in L. at any load P while the specimen is within the elastic zone.Yield point 屈服点 elongation 拉长；延伸Reduction 减少；降低 customary 通常的；惯例的Standardize 标准（规格）化 gauge 量规；标准；尺度Fillet 圆角；倒角 gauge length 标距；计算长度Grip 夹紧；夹牢 previously 以前的；预先地Dial 刻度盘 extensometer 应变计；引伸仪Plot 标绘；绘曲线 stress-strain curve 应力应变曲线（拉伸曲线）Ult