Abstract:The dynamic material characterization shows different macroscopic strain rate effects. The causal mechanisms cannot be identified at this level in most cases. Micro-tests allow a local transient analysis, which is illustrated in this article using the example of a long-fibre reinforced thermoplastic (LFRT). After a general introduction, the development and validation of a micro-test for a large strain rate range is presented. The validation explained for steel shows the advantage of the small sample for the dy… Show more
“…increases with higher strain rates, where F is the applied force and L the displacement. Additionally, Huberth et al 27 were able to develop a technique to test SFRP on a microscopic scale (with a specimen length of 1.1 mm). This can help to uncover the present micro-mechanics and the origin of specific influences on the failure behavior.…”
Section: Materials and Mechanicsmentioning
confidence: 99%
“…Figure 2.In the SFRP micro specimens just before failure the deformed material appears brighter. Strain rate of 0.0007/s (above) and 250/s (below) were applied 27. …”
A failure model for SFRP for FEM simulations is developed to describe the strain rate dependency, the influence of the local fiber orientation and of the stress state on the failure behavior. The material is considered as a continuum while internally calculating the micro-mechanics analytically. The described micro-mechanics are based on experimental observations and on analyzation with numerical studies. In particular the strain rate dependent delamination of fibers and matrix is incorporated in the model. The distortion energy density is defined as the driving value for failure and estimated by the model. This is achieved with the analytic solution by Eshelby for the stress field in the matrix and by introducing an additional phase for the plasticly deformed volume. The validation on characterization specimens as well as component test demonstrates that the influence of strain rate, fiber orientation, and stress state on the failure behavior can be described with only one material parameter, the critical distortion energy density.
“…increases with higher strain rates, where F is the applied force and L the displacement. Additionally, Huberth et al 27 were able to develop a technique to test SFRP on a microscopic scale (with a specimen length of 1.1 mm). This can help to uncover the present micro-mechanics and the origin of specific influences on the failure behavior.…”
Section: Materials and Mechanicsmentioning
confidence: 99%
“…Figure 2.In the SFRP micro specimens just before failure the deformed material appears brighter. Strain rate of 0.0007/s (above) and 250/s (below) were applied 27. …”
A failure model for SFRP for FEM simulations is developed to describe the strain rate dependency, the influence of the local fiber orientation and of the stress state on the failure behavior. The material is considered as a continuum while internally calculating the micro-mechanics analytically. The described micro-mechanics are based on experimental observations and on analyzation with numerical studies. In particular the strain rate dependent delamination of fibers and matrix is incorporated in the model. The distortion energy density is defined as the driving value for failure and estimated by the model. This is achieved with the analytic solution by Eshelby for the stress field in the matrix and by introducing an additional phase for the plasticly deformed volume. The validation on characterization specimens as well as component test demonstrates that the influence of strain rate, fiber orientation, and stress state on the failure behavior can be described with only one material parameter, the critical distortion energy density.
“…33–36 The distortion energyis often defined as the force F, which causes the deformation, integrated over the displacement L. But furthermore, in a recent study Hubert et al 37 presented a new method for testing microscopic specimens similar to the experiment performed by Duan et al 38 but on a smaller scale. Thereby the local deformation in inhomogeneous materials are made visible directly.…”
Section: Introductionmentioning
confidence: 99%
“…Figure 1.The test setup for the micro specimens (left) and the dimension of the specimen in mm (right) with a thickness of 0.35mm. 37 …”
For predicting the strain rate dependent failure of short fiber reinforced plastics (SFRP) a two-phase simulation model is developed using the finite element method and comparing the results to microscopic specimen tests for uniaxial tension under quasi-static (0.007/s) and dynamic loads (250/s). Experimentally the failure behavior of SFRP is observed to be strain rate dependent. The global strain at failure and the absorbed energy increase with strain rate. Moreover, locally an influence of the strain rate on the amount of material involved in the deformation can be observed. The suggested model can represent these effects accurately. Also, the present micro-mechanical effects and their influence on the strain distribution are investigated by unit cell simulations. Thereby the material model of the fibers, the matrix, and the boundary layer are varied respectively. These reveal the important role of strain rate dependent decohesion leading to a correct representation of the plastically deformed volume. Consequently, the distortion energy density is evaluated and is found to be constant at failure for all strain rates.
“…The requirements were implemented in the testing facility, IWM DynMicro. [10,11] The other advantage of the sample size is that the complete microstructure can be analysed using microcomputed tomography (μCT) images. Detailed geometric information about the microstructure of the composite can be obtained by methods of image processing.…”
The mechanical properties of fibre‐reinforced thermoplastics and their dependencies on the manufacturing process, fibre properties, fibre concentration and strain rate have been researched intensively for years in order to predict their macroscopic behaviour by numerical simulations as precisely as possible. Including the microstructure in both real and virtual experiments has improved prediction precision for injection‐moulded glass fibre‐reinforced thermoplastics significantly. In this work, we apply three established methods for characterisation and modelling to an injection‐moulded and to a 3D printed material. The geometric properties of the fibre component as fibre orientation, fibre length and fibre diameter distributions are identified by analysing reconstructed tomographic images. For comparing the fibre lengths, a recently suggested new method is applied. Based on segmentations of the tomographic images, we calculate the elastic stiffness of both composites numerically on the microscale. Finally, the mechanical behaviour of both materials is experimentally characterised by micro tensile tests. The simulation results agree well with the measured stiffness in case of the injection‐moulded material. However, for the 3D printed material, measurement and simulation differ strongly. The prediction from the simulation agrees with the values expected from the image analytic findings on the microstructure. Therefore, the differences in the measured behaviour have to be contributed to the matrix material. This proves demand for further research for 3D printed materials for predictable prototypes, preproduction series and possible serial application.
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