Elastic-plastic transition

Elastic-plastic transition It is the changes from recoverable elastic behavior to non-recoverable plastic strain which occurs on stressing a material beyond its yield point. 

Figure 17.2 shows a a-8 curve for LiF that illustrates an abrupt elastic-plastic transition. Plastic deformation begins at the upper yield point and there is a decrease in stress. At the lower yield point deformation continues at lower stress levels. This type of behavior is similar to that of some low-carbon steels as well as aluminum oxide and magnesium oxide at high temperatures. 

We will discuss here the anisotropic yield behaviour of oriented polymers but there is a need for a few preliminary remarks regarding the topic of yield in general. In describing the deformation of many crystalline materials, especially metals and ceramics, it is often convenient to introduce the idealisation of an elastic-plastic transition . The term elastic is used to describe the components of the strain which are proportional to the applied stresses, and which are completely recovered on removal of the stresses. Plastic strains are observed only for stresses greater than or equal to the yield stress and are not recovered on removal of the stress. The yield stress defines the elastic-plastic transition. 

The yield point for metals with gradual elastic-plastic transitions is constructed by drawing a straight line parallel to the elastic portion of the stress vs. strain curve at a specific strain offset, usually 0.002. The intersection of that line and the stress vs. strain curve gives rise to the yield strength, Oy, of the... 

In contrast to what is observed on Si02, table 3 below shows that N ion implantation actually decreases the critical load required for the onset of fracture failure in silicon. The on-load scratch traces also show an inflexion at the elastic-plastic transition at much lower load that correlates with final topography data as well. On sample 5 this is at 10 mN. There is also catastrophic failure at a higher applied load than the Lc values in Table 3. 

Some steels and other materials exhibit the tensile stress-strain behavior shown in Figure 6.10b. The elastic-plastic transition is very well defined and occurs abruptly in what is termed a yield point phenomenon. At the upper yield point, plastic deformation is initiated with an apparent decrease in engineering stress. Continued deformation fluctuates slightly about some constant stress value, termed the lower yield point, stress subsequently rises with increasing strain. For metals that display this effect, the yield strength is taken as the average stress that is associated with the lower yield point because it is well defined and relatively insensitive to the testing procedure. Thus, it is not necessary to employ the strain offset method for these materials. 

DE - A Two-Dimensional Eulerian Hydro-dynamic Code for Computing One-Component Reactive Hydrodynamic Problems , Los Alamos Scientific Laboratory Report LA-3629-MS (1966) 23b) C.L. Mader, "FORTRAN-SIN - A One-Dimensional Hydrodynamic Code for Problems Which Include Chemical Reactions, Elastic-Plastic Flow, Spalling, and Phase Transitions , Los Alamos Scientific Laboratory Report LA-3720(1967) 24) R.C. Sprowls, "Com-... 

The formation and evolution of multiple waves becomes more complicated when chemical reactions or phase transitions occur. Volume decreasing phase transformations cause the pressure at point B in Figure 2 and Figure 7 to decrease with time. This common phenomenon is known as elastic precursor decay in elastic-plastic wave system. [9] The timescale for this pressure decay depends primarily on the timescale for the chemical reaction or phase transition that gives rise to the 2" wave. 

The CDM has two additional features that allow it to represent fracture in rocks. First, there is a brittle/ductile transition pressure. Above this pressure, the rock behaves as an elastic/plastic ductile solid, the failure surface is independent of the level of damage, and the damage is not allowed to increase, even if the failure surface is exceeded. Second, the CDM allows for non-vanishing plastic volume strain to approximate the dilatancy observed in certain laboratory experiments on oil shale. 

FIGURE 41.8 Representative stress-strain curve for a cellular solid. The plateau region for compression in the case of elastomeric foam (a rubbery polymer) represents elastic buckling for an elastic-plastic foam (such as metallic foam), it represents plastic yield, and for an elastic-brittle foam (such as ceramic) it represents crushing. On the tension side, point A represents the transition between cell wall bending and cell wall alignment In elastomeric foam, the alignment occurs elastically, in elastic plastic foam it occurs plastically, and an elastic-brittle foam fractures at A. 

The dissipated energy i.e. both Aq and and also (Aq+ r), the load Fgy and deflection/gy at the transition from elastic to elastic—plastic material behaviour, the maximum load F ax and the deflection at the maximum load /max are the typical measures of the ICIT. 

Fundamental Properties of Polymers, Metals and Ceramics (e.g., strength in compression, tension and bending elasticity/plasticity failure mechanisms phase diagrams transition temperatures surface roughness hydrophobicity) Mechanical Properties of Biological Tissues (e.g., elastic viscoelastic, hysteresis, creep, stress relaxation)... 

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