The volume of plastics that are subjected to impact simulation has grown rapidly. In a previous paper, we discussed why different material models are needed to describe the highly varied behavior exhibited by these materials. In this paper, we cover the subject in more detail, exploring in depth, the nuances of commonly used LS-DYNA material models for plastics, covering important exceptions and criteria related to their use.
Ultra-high molecular weight polyethylene (UHMWPE) is used extensively in orthopedic applications within the human body. Components made from these materials are subject to complex loading over extended periods of time. Modeling of components used in such applications depends heavily on having material data under in-vivo conditions. We present mechanical and visco-elastic properties measured in saline at 37C. Comparisons to conventionally measured properties at room temperature are made.
LS-DYNA software contains a wealth of material models that allow for the simulation of transient phenomena. The Matereality® CAE Modeler is a generalized pre-processor software used to convert material property data into material parameters for different material models used in CAE. In a continuation of previously presented work, we discuss the extension of the CAE Modeler software to commonly used material models beyond MAT_024. Software enhancements include advanced point picking to perform extrapolations beyond the tested data, as well as the ability to fine-tune the material models while scrutinizing the trends shown in the underlying raw data. Advanced modeling features include the ability to tune the rate dependency as well as the initial response. Additional material models that are quite complex and difficult to calibrate are supported, including those for hyperelastic and viscoelastic behavior. As before, the written material cards are directly readable into the LS-DYNA software, but now they can also be stored and catalogued in a material card library for later reuse.
We seek to lay down a framework to help us understand the different behavioral classes of foams. Following a methodology that we previously applied to plastics, we will then attempt to propose the right LS-DYNA material models that best capture these behaviours. Guidelines for model selection will be presented as well as best practices for characterization. Limitations of existing material models will be discussed.
The profitability of a molded rubber product depends to a large extent on the mold efficiency. To achieve the maximum productivity, besides the larges possible number of cavities it is desirable to minimize the rubber consumption and to produce parts without defects.
Digital Image Correlation Techniques Enhance Composite Testing Capability. Store and Manage Properties of Structured Composites with a Matereality® Database.
Optical strain measurement for the mechanical characterization of polymers, and in particular of polyolefins, is becoming a common practice to determine the parameters to be used in a finite element analysis of crash problems. This experimental technique allows measuring the strain locally on the specimen, so that it is particularly suitable when the deformation is localized, as in the case of polymers: therefore a more accurate description of the behaviour of the material is obtained. By so doing, it is possible to describe the material constitutive law in terms of the true, local strain and of the true stress. As these data are those needed by the most complete material models developed for impact calculation, it is clear that this technique is particularly suitable for coupling with the most advanced material models currently available in the F.E. codes, as for instance with Mat 187 (SAMP-1) of LS-Dyna. The local measurement of the strain can also be used for evaluating the volume strain, whose evolution with the increasing strain shows that for PP-based material the deformation is not isochoric in most the cases. The observed increase in the material volume reflects the fact that voids generate and coalesce within the material, possibly resulting in fracture. The measure of the volume strain, computed as the trace of the strain tensor, is here used for determining the damage function utilized by the damage model implemented in SAMP-1. The effective stress is here estimated as the stress which would be measured if the deformation was isochoric, and it can be assessed on the basis of the measurement of the longitudinal local strain only. Corresponding to each value of longitudinal strain, the volume strain is then used to calculate the ratio between the effective and the true stress. Adopting this procedure, the damage function is thus determined without the needs of repeated loading-unloading tests used to derive the damage parameter from the unloading slope, which is furthermore difficult to be measured. As an application, the results of the numerical reproduction of a benchmark test, consisting in a drop test on a polypropylene box, are presented and discussed
