Stress offset yield

Stress, offset yield Also called engineering yield strength. The stress at which the strain exceeds by a specified amount (the offset, such as 0.1% of strain) or extension of the initial proportional part of the stress-strain curve. It is the force per unit area (MPa, psi, etc.). This measurement is useful for materials whose S-S curve (stress-strain) in the yield range is of gradual curvature. 

Considering that the stress-strain curves for most metallic materials are not significantly affected by temperature and strain rate, the common choice of the 0.2 % offset yield strength may be acceptable. But stress-strain curves for adhesives vary greatly with relative humidity (RH), ambient temperature, strain rate, and adhesive type. Thus, an alternative method is needed for determining the yield strength of adhesives and other materials that exhibit a continuous transition from the elastic to the inelastic regions. The method should be based on the fundamental principles of mechanics of materials. 

The yield strength (a load) or yield stress (a stress value) is the point at which plastic deformation occurs (point A, Figure 10.1 la). For most materials, the transition from elastic to plastic behaviour is rarely abrupt, and a single point does not mark the boundary between elastic and plastic deformation. In order to obtain a guide as to when a stress value passes that required for plastic deformation to occur, it is usual to select a value of the stress that leads to 0.2 % plastic strain (0.002 strain). This is also called the 0.2 % offset yield strength. [This value is arbi-... 

Some of these terms are illustrated in Fig. 2 While a number of them are rather cumbersome and pedantic, they do make clear precisely what is being considered. The new-standard has no definition for offset yield stress or proportional limit because the idea of trying to specify the extent of the initial linear portion of the stress-strain curve has been abandoned. It was in any case untenable for many plastics materials and of little practical value for the others. 

The appearance of a permanent set is said to mark a yield point, which indicates the upper limit of usefiilness for any material. Unlike some metals, in particular, the ferrous alloys, the drop-of-beam effect and a sharp knee in the stress-strain diagram are not exhibited by plastics. An arbitrary yield point is usually assigned to them. Typical of these arbitrary values is the 0.2% or the 1% offset yield stress (Figure 3.3a). 

Polymorphic transformations complicate the mechanical properties and their temperature dependence in cerium. The 0.2% offset yield strength data from Owen and Scott (1976) shown in fig. 8.18 reveal the effect of the y(f.c.c.) to /3(d.h.c.p.) transformation beginning at about 280 K. The yield stress tends to increase with increased amount of p phase as the temperature decreases. At approximately 110 K the yield strength rises dramatically in association with the transformation of the remaining y(f.c.c., a = 5.16) to a(f.c.c., a = 4.85), see ch. 4 section 2.4.5. With decreasing temperature the ultimate tensile strength rises rapidly at about 375 K. This rise probably reflects deformation-induced 7 to J3... 

In the simulation models, it is easy to see that the main differences are direction, size and zone of stress and yield area that all offset centralized. Figure 2c and d, show that the difference of tensile stress in distribution. The two models both have the asymmetries of tensile stress concentration around the goaf The area of tensile stress is larger in model b and extends to a higher position in the overburden rock mass, while the tensile stress is limited in the area of the overburden rock mass in model a and forms a narrow stretching zone on the uphill side above the working face. These differences reveal that alters of symmetry comes from coal seam inclination and the stretching band on the uphill caused by the inclination of the unconformity. 

The yield strength (YS) of a material, denoted or is the stress corresponding to the end of the linear portion of the stress-strain curve for the uniaxial tensile test. The 0.002 (or 0.001) proof strength (i.e., 0.2% offset yield strength) is used when the material shows no pronounced yield point. Afterward any additional stress leads to a residual permanent deformation of the material i.e., plastic deformation) indicated by a hysteresis. 

Analysis of the change in the mechanical properties of high-density polyethylene submitted to gamma irradiation shows that a 5% offset affects yield stress, and yield stress obtained from compression tests increased as the adsorbed radiation dose... 

Yield Strength n The stress at which a material exhibits a specified limiting deviation from the proportionality of stress to strain. Unless otherwise specified, this stress will be the stress at the yield point (ASTM D 638 and D 638M). See also Offset Yield Strength. (Shah V, Handbook of Plastics Testing Technology, John Wiley and Sons, New York, 1998, www.astm.org)... 

As-rolled 25 mm (1 in.) plate. Initial stress = 0.2% offset yield strength at the test temperature. 

It is possible to summarize the creep data by comparing the times to 1.0% total strain, as a function of stress, in the data shown in Fig. 1.3-16. The reproducibility of creep data for this material is indicated by the separate curves shown in Fig. 13-17. It may be seen that quite good correlation between the creep curves is obtained at the lower stress values. Some scatter in time to rupture occurs at 25,000 psi, a stress which corresponds to the 0.2% offset yield strength at this temperature. Such scatter is to be expected at this high stress level. 

Table 3 lists the average tensile properties of the 13 specimens, including standard deviation (STD) and coefficient of variation (COV) with symbols of E = modulus of elasticity, Oyo.2% and e o.2% = yi W stress and yield strain at 0.2% offset, a = tensile strength, and e = elongation at break. 

Elements that can dissolve in copper, such as zinc, tin, and nickel for example, increase annealed strength by varying amounts depending on the element and the quantity in solution. The effect of selected solution hardening elements on tensile properties of annealed copper aUoys is iUustrated by the data in Table 4, where the yield strength is the stress at 0.2% offset strain in a tensile test. 

---