This book is intended to be a companion to the NAFEMS book, "An Introduction to the Use of Material Models in FE". It informs Finite Element Analysis users of the manner and methodologies by which materials are tested in order to calibrate material models currently implemented in various FEA programs. While the authors seek first to satisfy the basic material models outlined in the companion book, they make important extensions to FEA used in currently active areas including explicit simulation.
We present a perspective on material modeling as applied to mold analysis requirements. Melt-solid transitions and the case for a unified material model are discussed, along with prediction of post-filling material behavior and shrinkage, and the impact of viscous heating on flow behavior and material degradation.
DatapointLabs' TestPaks (material testing + model calibration + Abaqus input decks) for rate-dependent, hyperelastic, viscoelastic, NVH, and the use of Abaqus CAE Modeler to transform raw data into material cards will be presented. A representative from Idiada will present a case study explaining the use of DatapointLabs’ material data and TestPaks for simulation.
Hyperelastic models are used extensively in the finite element analysis of rubber and elastomers. These models need to be able to describe elastomeric behavior at large deformations and under different modes of deformation. In order to accomplish this daunting task, material models have been presented that can mathematically describe this behavior [1]. There are several in common use today, notably, the Mooney-Rivlin, Ogden and Arruda Boyce. Each of these has advantages that we will discuss in this article. Further, we will examine the applicability of a particular material model for a given modeling situation.
"Recently new materials were introduced to enhance different aspects of automotive safety while minimizing the
weight added to the vehicle. Such foams are no longer isotropic but typically show a preferred strong direction due
to their manufacturing process. Different stress/ strain curves are obtained from material testing in different
directions. A new material model was added to the LS-DYNA code in order to allow a correct numerical simulation
of such materials. Ease-of-use was a primary concern in the development of this user-subroutine: we required stress/
strain curves from material testing to be directly usable as input parameters for the numerical model without
conversion. The user-subroutine is implemented as
MAT_TRANSVERSELY_ANISOTROPIC_CRUSHABLE_FOAM, Mat law 142 in LS-DYNA Version 960-1106.
In this paper we summarize the background of the material law and illustrate some applications in the field of
interior head-impact. The obvious advantage of incorporating such detail in the simulation lies in the numerical
assessment of impacts that are slightly offset with respect to the foam’s primary strength direction."
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.
"Today the automotive industry is faced with the demand to build light fuel-efficient vehicles while
optimizing its crashworthiness and stiffness. A wide variety of new metallic and polymeric materials
have been introduced to account for these increased requirements. Numerical analysis can
significantly support this process if the analysis is really predictive. Within the numerical model a
correct characterization of the material behaviour – including elasto-viscoplastic behaviour and failure
- is substantial. The particular behaviour of each material group must be covered by the material
model.
The user material model MF GenYld+CrachFEM allows for a modular combination of
phenomenological models (yield locus, strain hardening, damage evolution, criteria for fracture
initiation) to give an adequate representation of technical materials. This material model can be linked
to LS-DYNA when using the explicit-dynamic time integration scheme.
This paper gives an overview on the material characterization of ultra high strength steels (with focus
on failure prediction), non-reinforced polymers (with focus on anisotropic hardening of polymers), and
structural foams (with focus on compressibility and stress dependent damage evolution) with respect
to crash simulation. It will be shown that a comprehensive material model - including damage and
failure behaviour - enables a predictive simulation without iterative calibration of material parameters.
A testing programme has been done for each material group in order to allow a fitting of the
parameters of the material model first. In a second step different component tests have been carried
out, which were part of a systematic procedure to validate the appropriate predictions of the crash
behaviour with LS-Dyna and user material MF_GenYld+CrachFEM for each material group."
