Search

This paper presents experimental results from three-point bending tests for a composite made of quadriaxial glass fiber fabrics and an epoxy resin. Two composites were tested, one with 8 layers and the other with 16 layers; both had the same matrix (the epoxy resin). Tests were carried out, using five different test rates from 10 mm/min to 1000 mm/min. The following parameters were recorded and calculated: Young's modulus, flexural stress, flexural strain, energy, force, and all four for the first peak. The experimental data reveal no sensitivity for these materials based on the test rates, at least for the analyzed range; but, the characteristics for the thicker composite, with 16 layers of fabric, are slightly lower than those for the thinner composite, with 8 layers. The results pointed out that, for the same thickness of composite, certain characteristics, such as stress at the first peak, the flexural modulus, strain at the first peak, and energy at the first peak, are not sensitive to the test rate in the range 10–1000 mm/min. The energy at the first peak is double for the 16-layer composite compared to the 8-layer composite, but the specific energy (as energy on cross-sectional area) has close values: 103.47 kJ/m2 for the 8-layer composite and 106.51 kJ/m2 for the 16-layer composite. The results recommend this composite for applications in components with resistance to bending or for low-velocity impact protection. [ABSTRACT FROM AUTHOR]

This paper presents an analysis of 3D amplitude and functional parameters for worn surfaces of composites with polyamide 6 as matrix and different glass bead concentrations (0%, 2.5%, 5%, 10%, 20%, 30% and 50%wt). The worn surfaces after dry sliding of a steel pin on a disk, for 10 km, at constant velocity (0.5 m/s, 1 m/s and 1.5 m/s) and under an average pressure of 1 MPa. There were done two tests under the same conditions. On each worn track, there were investigated three surfaces of 500 μm x 500 μm with a contact profilometer. The number of points on the scan line was 200 points and the step between lines was 5μm. The following amplitude parameters were measured and calculated for assessed surfaces: the arithmetic mean deviation, Sa, the root mean square deviation, Sq, the maximum height of surface prominence, Sp, the maximum surface depth, Sv, the maximum height, St, the skewness factor, Ssk and the kurtosis, Sku. The discussed functional parameters are the reduced peak height, Spk, the height of the core of the surface, Sk and the depth of the valley zone, Svk. The comparison of their values makes posible to evaluate if the worn surface could function in a new running or the replacement of the component is recommended. Considering that machine components have intermittent operation, these worn surfaces becoming initial surfaces for the following cycle of contact operation. Based on the average values of amplitude and functional parameters, it was found that a relatively good surface quality is preserved for concentrations of 10...30%wt glass beads, for v=0.5...1 m/s (Sa and Sq having similar trend); for lower concentrations and for 50% glass beads, the parameter values increase but without identifying a distinct relationship with the working regime, especially for 2.5 and 5% glass beads. [ABSTRACT FROM AUTHOR]

This paper presents an analysis based on experimental data for pointing out the behavior of rapeseed oil when it is additivated with a modifier of friction and wear, the nano hexagonal Boron nitride. All tests are done on a four-ball machine, in mild regime. Test parameters were sliding velocity (0.38 m/s, 0.53 m/s, 0.69 m/s, corresponding to the spindle rotational speed of the four-ball machine of 1000 rpm, 1400 rpm, 1800 rpm (±10 rpm),), force (100 N – 300 N), test duration 1 h. There were calculated the average friction coefficient during the test and the average wear scar diameter (WSD) for each test. The same test parameters were done twice and the values in this paper are the average of these two tests. Wear was discussed for the same velocity range, in terms of WSD, but for comparing tests with different sliding velocity (implicitly, different sliding distances), there was used the wear rate of the wear scar diameter. The results on wear parameters, using additivated rapeseed oil, do not show spectacular results for the parameters tested in this study, but underline the “insensitivity” of the lubricants to the variation of the test regime (especially with respect to sliding speed), which is desirable for certain applications. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

This paper compares two models for ballistic impact on unidirectional fabrics in order to evaluate their influence in making the simulation closer to actual events. The importance of including the effect of fibers and yarns architecture, their properties and those for their matrix in the model is highlighted by figures showing equivalent stress distributions at different moments of the impact and images from the run simulations. It resulted that the model with interlaminar delamination is more suitable for these simulations considering the stress distribution analyzed for the main yarns of the panel. [ABSTRACT FROM AUTHOR]

This paper presents and analysis of several 3D amplitude parameters of the texture, measured or calculated for the entire wear scar of the stationary balls used in four-ball tester: Sa, St, Sv, Sp, Ssk and Sku. The authors investigated balls tested in rapeseed oil, rapeseed oil + 1% TiO2 and rapeseed oil +1 % ZnO in order to establish the influence of the testing regime (sliding velocity and force on the main shaft of the tester) on the surface quality at the end of the test, by the help of several amplitude 3D parameters. Qualitatively, the wear process is uniform on the balls in one test, because spread ranges of the discussed parameters are small enough. At low force (F=100 N), corroborating the values of the studied amplitude parameters, it could be concluded that wear processes take place on the peaks of the texture. The Sa parameter is not affected by additivation for v=0.38 m/s and forces from F=100 N to F=300 N. At high sliding velocity, a slope change of both parameters is observed between F=200 N and F=300 N. If the wear is approximately the same at the test end for F=300 N, the roughness of the wear trace increases greatly when the rapessed oil is additivated with, meaning that nano particle of TiO2 agglomerate and participate in the formation of a rougher texture. Lubricant with ZnO keeps the average roughness Sa close to that obtained with nonadditivated rapeseed oil. In order to assess the quality of a surface as close as possible to reality, using 3D parameters, the profilometer pitch should be as fine as possible and the area of investigation as large as possible. However, a trade-off has to be done between the step size, the investigation area and, of course, time to fulfill the study. The Sku parameter shows if there are large isolated peaks and Ssk indicates if the peak frequency is high. For the case of worn surfaces, it is the values of the parameters Ssk, Sku, St, Sp and Sv that are of interest, because high peaks affect the tribological parameters. The surface quality when additivated with 1% TiO2 is much better up to F=300 N. Additivation with 1% TiO2 is recommended for low loads, F=100 N and F=200 N, for point contacts. Study should be completed with the same investigation in severe regime where nano-additives should improve seizure limit of load. [ABSTRACT FROM AUTHOR]

Pressure tanks are closed containers, in which fluids are kept at a pressure higher than atmospheric pressure or under vacuum, at different temperatures. They are used for storing various fluids or gases, transporting them or for various technological purposes. Based on the simulation results, the influence of the container thickness and internal pressure on the distributions of the maximum values of total deformations and equivalent stresses were analyzed. For the range of input parameters analyzed (internal gas pressure and container shell thickness), the construction and design solution that meets the requirements of the design (maximum gas pressure of 19.6 bar, testing pressure (with water) 29.6 bar, internal volume 16850 liters, nominal diameter of 2000 mm and length of 5627 mm) is that with a container having a shell thickness of 16 mm to meet the safety criteria provided in SR EN 13445-3:2014 with subsequent amendments. [ABSTRACT FROM AUTHOR]

This paper presents a characterization of PA6 and the blend PA6+EPDM (60/40) by tensile tests in order to evaluate several mechanical properties for impact resistance applications. Results were found to be dependend on test rate (10 mm/min, 250 mm/min and 1000 mm/mm). SEM investigation point out a homogenous structure. The blend has better value of energy at break, for the higher test speed: for v=250 mm/min this characteristic has the value of energy at break 29.7 J and the blend has 76.3 J. At 1000 mm/min, PA6 has this charcateristic of 20 J, but for the blend, it is almost insensitive for the two higher test speeds (76.3 J at 250 mm/min and 72.4 J at 1000 mm/min, respectively) as compared to the neat polymer that decreases this feature when thr test spee increases. At the lowest teste speed, the values of energy at break for the materials in this study are close (90.2 J for PA6 and 87.7 J for the blend). The results from tensile tests pointed out that the formulated blend is recommended for impact resistance applications. [ABSTRACT FROM AUTHOR]

This paper presents an analysis of data resulting from the same material constitutive model, based on experimental data and model developed by Johnson and Cook. The same case of impacting a cylindrical body on a perfectly rigid target was run with four different mesh size (2 mm, 1 mm, 0.5 mm and 0.25 mm). Here, the comparing criterion was the maximum value of von Mises stress and the authors pointed out that the finest mesh here presented is closer to reality. Depending on the case application the engineers could adopt a finer or coarse mesh, but not so coarse to denaturate the reality of body deformation and failure. How to decide? Having performant computer resources (hardware and software) and running several mesh in order to notice the convergence of one parameter or, more reliable, a set of criteria that could include qualitative resemblance with actual bodies as concerning failure and deformation, experimental dat on strain, yield and failure of the involved materials, values of stress and strain, at the same time moments. From this study the following conclusions were formulated: finer mesh presents a earlier failure in time and calculated a higher stress for these moment. [ABSTRACT FROM AUTHOR]

The objective of this paper is to simulate the behavior of unidirectional fabrics, as realistic as possible, in order to be able to use the model in designing impact-resistant packages. There was discussed the influence of the number of layer and the impact velocity on several characteristics as residual velocity of the projectile, its acceleration and the maximum values of von Mises stresses during the impact. Three cases were considered: one layer, two layers and four layers. For all cases, the impact velocity was varied between 100 m/s and 400 m/s, with an increment of 100 m/s, in order to simulate how the panel is damaged. The higher the impact velocity, the stressed area increases when the stress distribution is compared to the stress distribution obtained for v0=100 m/s to that for v0=300 m/s. At the highest velocity for which the simulation was run, the stressed area has diminished. For the four layer package, for lower velocities, the residual velocity has a lower percentage of the impact velocity, but at high speeds, for this package, the reduction of the residual is even lower (2.7% at v0=300 m/s and only 1.75% at v0=400 m/s). [ABSTRACT FROM AUTHOR]

This paper presents results from numerical and experimental investigation on Charpy tests in order to point out failure mechanisms and to evaluate new polymeric blends PP + PA6 + EPDM. Charpy tests were done for initial velocity of the impactor of 0.96 m/s and its mass of 3.219 kg and these data were also introduced in the finite element model. The proposed model takes into account the system of four balls, including support and the ring of fixing the three balls and it has a finer discretization of the impact area to highlight the mechanisms of failure and their development in time. The constitutive models for four materials (polypropylene with 1% Kritilen, two blends PP + PA6 + EPDM and a blend PA6 + EPDM) were derived from tensile tests. Running simulations for each constitutive model of material makes possible to differentiate the destruction mechanisms according to the material introduced in the simulation, including the initiation and the development of the crack(s), based on equivalent plastic strain at break (EPS) for each material. The validation of the model and the simulation results were done qualitatively, analyzing the shape of broken surfaces and comparing them to SEM images and quantitatively by comparing the impact duration, energy absorbed by the sample, the value of maximum force during impact. The duration of the destruction of the specimen is longer than the actual one, explainable by the fact that the material model does not take into account the influence of the material deformation speed in Charpy test, the model being designed with the help of tests done at 0.016 m/s (1000 mm/min) (maximum strain rate for the tensile tests). Experimental results are encouraging for recommending the blends 20% PP + 42% PA6 + 28% EPDM and 60% PA6 + 40% EPDM as materials for impact protection at low velocity (1 m/s). Simulation results are closer to the experimental ones for the more brittle tested materials (with less content of PA6 and EPDM) and more distanced for the more ductile materials (with higher content of PA6 and EPDM). [ABSTRACT FROM AUTHOR]