August 24, 2015 | by Massimo Nutini | views 3871
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
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Mechanical
Plastics
Rate Dependency
Yielding/Failure analysis
Automotive
High Speed Testing
LS-DYNA
Research Papers
August 24, 2015 | by Massimo Nutini | views 3708
Glass-fiber-reinforced polypropylene (GF PP) materials are increasingly being used by customers to replace metal and engineering polymers in structural automotive applications. Like all glass-fiber reinforced thermoplastics, GF PP products can show anisotropy caused by fiber orientation that is induced by the injection process. Taking into account fiber orientation in the simulations enables designers to improve the accuracy of the analyses. This can help prevent arbitrary choices and assumptions when setting material parameters, which become mandatory when an isotropic material law is used. The method proposed in this paper takes advantage of the availability within Ls-dyna of an anisotropic material law (MAT_103), which allows simplified modeling to address critical issues. This law was not developed to address the problem discussed here.
Therefore, this paper illustrates a simplified approach. The presence of glass reinforced fibers is taken into account by running a mold-filling analysis, and then transferring the material flow orientation in to the structural simulation as a material angle. The dependence of the material failure strain on the material orientation can be also easily modeled through a user subroutine. Finally, the approach only requires simple material data based on basic tensile tests; the material law parameters are then identified through optimization techniques. Although this approach is based on some simplifying assumptions, its application is quick and can help the designer obtain more accurate results with respect to the traditional isotropic approach. A selection of validation tests is then proposed that show reliable predictions using limited additional computational effort.
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Mechanical
Plastics
Rate Dependency
Automotive
High Speed Testing
LS-DYNA
Research Papers
August 24, 2015 | by Sigmasoft | views 3645
The tempering layout for injection molds is often designed departing from previous experiences. The manufacturing feasibility is the main driver when deciding where to place cooling lines. However, often the relevance of the tempering in the process profitability or in the part quality is underestimated, and due to the lack of better information sometimes the resulting tempering performs far from the optimum. As a consequence, the molding efficiency is reduced, the part quality is compromised and, once the mold is already built, sometimes expensive trial-and-error is required to bring the mold to an optimum configuration.
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Rheology
Thermal
Plastics
Automotive
Biomedical
Injection Molding
SIGMASOFT
Newsletters
August 24, 2015 | by Sigmasoft | views 3942
As the demand for functional integration and the need of design differentiation in manufactured products increase, the complexity of plastic parts increases as well; thus some previous knowledge on effective ejection systems becomes insufficient and the challenges in the design of ejection systems grow consistently.
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Rheology
Plastics
Rubbers
Visco-elastic
Automotive
Biomedical
Injection Molding
SIGMASOFT
Newsletters
August 24, 2015 | by Sigmasoft | views 3983
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.
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Rheology
Rubbers
Automotive
Biomedical
Injection Molding
SIGMASOFT
Newsletters
August 24, 2015 | by Altair Engineering | views 3303
Import your Matereality CAE Material cards directly into HyperWorks.
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Presentations
August 10, 2015 | by Tony Abbey | views 3321
Even with powerful modern computers, there is often a motivation to use simplifying techniques in structural finite element analysis (FEA).
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Structural Analysis
August 10, 2015 | by Tony Abbey | views 4301
I was recently tasked with creating material to explain what Verification and Validation (V&V) are in relation to FEA (finite element analysis).
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Validation
July 31, 2015 | by Massimo Nutini | views 3606
Questo articolo si propone di illustrare l’importanza dell’utilizzo di metodi per la misura
delle proprietà locali del materiale per determinarne la legge di comportamento.
Vengono di seguito presentati alcuni esempi che evidenziano quanto più accurate
e realistiche siano le simulazioni numeriche di test di trazione ad alta velocità su provini
di poliolefine, quando vengano utilizzate proprietà dei materiali rilevate con misure locali,
utilizzando metodi ottici. La disponibilità di misure locali e più accurate evidenzia come sia
necessario che nei codici di calcolo commerciali vengano implementate delle leggi
di materiale più sofisticate di quelle disponibili attualmente, che sono state per lo più
originariamente sviluppate per materiali metallici, e dunque non riescono sempre a predire
correttamente il comportamento dei componenti in materiali polimerici.
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Mechanical
Plastics
Rate Dependency
Automotive
High Speed Testing
LS-DYNA
Research Papers
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