3.2.1 Uniformly loaded, elastic-plastic plate

Product: ABAQUS/Standard  

This example is intended to serve two functions: to verify the coding of a standard rate-independent plasticity theory for metals and to assess the accuracy of the integration of the plasticity equations, especially in the case of nonproportional stressing. Integration of elastic-plastic material models is a potential source of error in numerical structural analysis. See, for example, the discussions by Krieg and Krieg (1977) and Schreyer et al. (1979). Usually the error is most severe when kinematic hardening is used in plane stress with nonproportional stressing (perhaps because of the complexity of the motion of the stress point and yield surface in stress space in this theory). This example contains two such problems. The exact solutions are available for both problems (Foster Wheeler report, 1972). Experience with a number of other computer programs has suggested that the second example, in particular, is a severe test of the numerical implementation of the plasticity theory. Both problems involve states of uniform plane stress and, hence, are done here by using a single plane stress element.

Problem description

Model and loading

The geometries and loading distributions for the unixial and biaxial cases are described below.

Case 1—Uniaxial loading

Figure 3.2.1–1 shows the geometry for this case. Two types of meshes are provided: a single-element mesh using higher-order plane stress and shell elements (CPS8R, S8R5, S9R5, and STRI65) and a mesh using linear shell and continuum shell elements (S4R and SC8R). Two edges have simple support. The load history is shown in Figure 3.2.1–2 and is prescribed with the *AMPLITUDE option (Amplitude curves, Section 27.1.2 of the ABAQUS Analysis User's Manual). The load distribution is a uniform, direct stress on the element edge. Since the strain should be uniform, the edge nodes are constrained using the *EQUATION option (Linear constraint equations, Section 28.2.1 of the ABAQUS Analysis User's Manual) to move together in the direction normal to the edge. Then the total load on the edge is simply given on one of the edge nodes.

Case 2—Biaxial loading

The case is set up with the same geometric model (Figure 3.2.1–1). However, the loading is more complex (see Figure 3.2.1–2).

First, the plate is loaded into the plastic range in uniaxial tension in the x-direction, unloaded slightly, and reloaded. Biaxial loading then follows, with and prescribed, as shown in Figure 3.2.1–2, so that the quantity remains constant at 276 MPa (40000 lb/in2). This loading is defined by the *AMPLITUDE option by reading in a file of values previously calculated in the small program AMP (see elasticplasticplate_amplitude.f).

Results and discussion

Input files

References

Table

Table 3.2.1–1 Some results for uniaxial load.

Load incrementNumber of iterations (10–3)
(MPa)(lb/in2)(ABAQUS)(exact)
1168.9471000000
21103.422150000.5000.500
31137.895200001.0001.000
41172.369250001.5001.500
5386.529125501.5001.500
620.691001.0101.010
73103.77150501.0101.010
82206.83300002.000not shown
93103.77150502.000not shown
1020.691001.0101.010


Figures

Figure 3.2.1–1 Geometry and material models for plasticity test cases.

Figure 3.2.1–2 Load histories.

Figure 3.2.1–3 versus , biaxially loaded plate.