This paper presents preliminary results and discussion on two aramid fabrics in order to establis... more This paper presents preliminary results and discussion on two aramid fabrics in order to establish their stab resistance when used as panels with different numbers of layers. Twaron fabrics SRM509 and CT736CMP, were arranged in 16 and 20 layers and in a combination of them (10 layers SRM509 and 10 layers CT736CMP). Samples of 130 mm x 130 mm were cut from the fabrics, weighed and measured for thickness. All tests were done for an impact energy of 24 J (the resulting impact velocity being 3 m/s). The blade had the geometry recommended in the standard Stab Resistance of Personal Body Armor NIJ Standard-0115.00 as P1. The conclusion of this analysis is that the better behavior to stab is obtained for panels that have higher gradients in time, for all four characteristics here discussed: force, displacement, absorbed energy and velocity. When using hybrid panels, the results could intermediate those of the components, this solution could be recommended for reasons as price, weight.
This paper presents an analysis of an isothermal model for an impact simulation in order to use t... more This paper presents an analysis of an isothermal model for an impact simulation in order to use the results for virtually optimizing the thickness of the panel for the same threat. The target has a stratified structure; the connection between layers is "bonded", with "breakable" detachment when there is exceeded a value for tensile stress and shear stress, introduced with the value of 90 MPa for tensile loading and 60 MPa for shear stress, these being characteristic values for the resin used for attaching the layers in the actual panel. Using Explicit Dynamics Ansys, it is possible to distinguish the stages of the impact process and how they depend on panel thickness. All bodies involved in impact are deformable, the bullet materials having a Johnson-Cook model and the layer being characterized. Even if the layer material model was simplified to a hardening isotropic bilinear model with data from the literature, the results were validated by the number of layers destroyed for the partially penetrated panels and by the size of the delamination on the back of the last layer. This simulation is useful for reducing the number of initial tests for evaluating the ballistic resistance.
This paper presents results on tribological characteristics for polymer blends made of polybutyle... more This paper presents results on tribological characteristics for polymer blends made of polybutylene terephthalate (PBT) and polytetrafluoroethylene (PTFE). This blend is relatively new in research as PBT has restricted processability because of its processing temperature near the degradation one. Tests were done block-on-ring tribotester, in dry regime, the variables being the PTFE concentration (0%, 5%, 10% and 15%wt) and the sliding regime parameters (load: 1 N, 2.5 N and 5 N, the sliding speed: 0.25 m/s, 0.5 m/s and 0.75 m/s, and the sliding distance: 2500 m, 5000 m and 7500 m). Results are encouraging as PBT as neat polymer has very good tribological characteristics in terms of friction coefficient and wear rate. SEM investigation reveals a quite uniform dispersion of PTFE drops in the PBT matrix.
The issue of impact simulation results from the fact that the impact load is unique and the desig... more The issue of impact simulation results from the fact that the impact load is unique and the designed system or element is requested not to fail only once or a small number of loadings. Tests for assessments of the degree of impact protection are expensive and numerous because they require a high probability of impact resistence. In the literature, there are models at the micro level (at fiber level), at the meso level (multi-fiber yarns, several fibers or by evaluating the behavior of the fibers to a monobloc yarn, as is the case with this simulation) and at the macro level (the behavior of element or system is done with some equivalences concerning the material model). This paper presents comparative results of the axis and on the edge of a yarn considered monoblock and isotropic to highlight the differences in the mechanisms of destruction of the yarn and in the evolution of the distribution of equivalent stress, highlighting the differences in the simulation of these two cases ex...
This paper presents preliminary results and discussion on two aramid fabrics in order to establis... more This paper presents preliminary results and discussion on two aramid fabrics in order to establish their stab resistance when used as panels with different numbers of layers. Twaron fabrics SRM509 and CT736CMP, were arranged in 16 and 20 layers and in a combination of them (10 layers SRM509 and 10 layers CT736CMP). Samples of 130 mm x 130 mm were cut from the fabrics, weighed and measured for thickness. All tests were done for an impact energy of 24 J (the resulting impact velocity being 3 m/s). The blade had the geometry recommended in the standard Stab Resistance of Personal Body Armor NIJ Standard-0115.00 as P1. The conclusion of this analysis is that the better behavior to stab is obtained for panels that have higher gradients in time, for all four characteristics here discussed: force, displacement, absorbed energy and velocity. When using hybrid panels, the results could intermediate those of the components, this solution could be recommended for reasons as price, weight.
This paper presents an analysis of an isothermal model for an impact simulation in order to use t... more This paper presents an analysis of an isothermal model for an impact simulation in order to use the results for virtually optimizing the thickness of the panel for the same threat. The target has a stratified structure; the connection between layers is "bonded", with "breakable" detachment when there is exceeded a value for tensile stress and shear stress, introduced with the value of 90 MPa for tensile loading and 60 MPa for shear stress, these being characteristic values for the resin used for attaching the layers in the actual panel. Using Explicit Dynamics Ansys, it is possible to distinguish the stages of the impact process and how they depend on panel thickness. All bodies involved in impact are deformable, the bullet materials having a Johnson-Cook model and the layer being characterized. Even if the layer material model was simplified to a hardening isotropic bilinear model with data from the literature, the results were validated by the number of layers destroyed for the partially penetrated panels and by the size of the delamination on the back of the last layer. This simulation is useful for reducing the number of initial tests for evaluating the ballistic resistance.
This paper presents results on tribological characteristics for polymer blends made of polybutyle... more This paper presents results on tribological characteristics for polymer blends made of polybutylene terephthalate (PBT) and polytetrafluoroethylene (PTFE). This blend is relatively new in research as PBT has restricted processability because of its processing temperature near the degradation one. Tests were done block-on-ring tribotester, in dry regime, the variables being the PTFE concentration (0%, 5%, 10% and 15%wt) and the sliding regime parameters (load: 1 N, 2.5 N and 5 N, the sliding speed: 0.25 m/s, 0.5 m/s and 0.75 m/s, and the sliding distance: 2500 m, 5000 m and 7500 m). Results are encouraging as PBT as neat polymer has very good tribological characteristics in terms of friction coefficient and wear rate. SEM investigation reveals a quite uniform dispersion of PTFE drops in the PBT matrix.
The issue of impact simulation results from the fact that the impact load is unique and the desig... more The issue of impact simulation results from the fact that the impact load is unique and the designed system or element is requested not to fail only once or a small number of loadings. Tests for assessments of the degree of impact protection are expensive and numerous because they require a high probability of impact resistence. In the literature, there are models at the micro level (at fiber level), at the meso level (multi-fiber yarns, several fibers or by evaluating the behavior of the fibers to a monobloc yarn, as is the case with this simulation) and at the macro level (the behavior of element or system is done with some equivalences concerning the material model). This paper presents comparative results of the axis and on the edge of a yarn considered monoblock and isotropic to highlight the differences in the mechanisms of destruction of the yarn and in the evolution of the distribution of equivalent stress, highlighting the differences in the simulation of these two cases ex...
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