The effect of perforations on the stress wave propagation characteristics of multilayered materials

The effect of perforated interlayers on the stress wave transmission of multilayered materials was investigated both experimentally and numerically using the Split Hopkinson pressure bar (SHPB) testing. The multilayer combinations consisted of a ceramic face plate and a glass/epoxy backing plate with a laterally constrained low modulus solid or perforated rubber and Teflon interlayer. The perforations on rubber interlayer delayed the stress rise time and reduced the magnitude of the transmitted stress wave at low strains, while the perforations allowed the passage of relatively high transmitted stresses at large strains similar to the solid rubber interlayer. It was concluded that the effect of perforations were somewhat less pronounced in Teflon interlayer configuration, arising from its relatively low Poisson's ratio. It was finally shown that SHPB testing accompanied with the numerical simulations can be used to analyze the effect of compliant interlayer insertion in the multilayered structures. © The Author(s) 2015

Calcined and natural frustules filled epoxy matrices: The effect of volume fraction on the tensile and compression behavior

The effects of calcined diatom (CD) and natural diatom (ND) frustules filling (0–12 vol.%) on the quasistatic tensile and quasi-static and high strain rate compression behavior of an epoxy matrix were investigated experimentally. The high strain rate testing of frustules-filled and neat epoxy samples was performed in a compression Split Hopkinson Pressure Bar set-up. The frustules filling increased the stress values at a constant strain and decreased the tensile failure strains of the epoxy matrix. Compression tests results showed that frustules filling of epoxy increased both elastic modulus and yield strength values at quasi-static and high strain rates. While, a higher strengthening effect and strain rate sensitivity were found with ND frustules filling. Microscopic observations revealed two main compression deformation modes at quasi-static strain rates: the debonding of the frustules from the epoxy and/or crushing of the frustules. However, the failure of the filled composites at high strain rates was dominated by the fracture of epoxy matrix

Processing and compression testing of Ti6Al4V foams for biomedical applications

Open cell Ti6Al4V foams (60% porosity) were prepared at sintering temperatures between 1,200 and 1,350 °C using ammonium bicarbonate particles (315–500 μm) as space holder. The resulting cellular structure of the foams showed bimodal pore size distribution, comprising macropores (300–500 μm) and micropores (1–30 μm). Compression tests have shown that increasing sintering temperature increased the elastic modulus, yield and compressive strength, and failure strain of foams. The improvements in the mechanical properties of foams prepared using smaller size Ti64 powder with bimodal particle distribution were attributed to the increased number of sintering necks and contact areas between the particles. Finally, the strength of foams sintered at 1,350 °C was found to satisfy the strength requirement for cancellous bone replacement.Technology Development Foundation of Turkey (TTGV) for the grant #TTGV-102/T1

Quasi-static axial crushing behavior of aluminum closed cell foam-filled multi-packed aluminum and composite/aluminum hybrid tubes

The axial crushing behavior of empty and Al close-cell foam-filled Al multi-tube designs (hexagonal and square) and E-glass woven fabric polyester composite and Al hybrid tubes were investigated through quasi-static compression testing. The effects of foam filling on the deformation mode and the crushing and average crushing loads of single tubes and multi-tube designs were determined. Although foam filling increased the energy absorption in single Al tube and multi-tube designs, it was not effective in increasing the specific absorbed energy over that of the empty Al tube. However, multi-tube designs were found to be energetically more effective than single tubes at similar foam filler densities, proving a higher interaction effect in multi-tube designs. Empty composite and empty hybrid tubes crushed predominantly in progressive crushing mode, without applying any triggering mechanism. Foam filling was found to be ineffective in increasing the crushing loads of the composite tubes over the sum of the crushing loads of empty composite tube and foam. However, foam filling stabilized the composite progressive crushing mode. In empty hybrid tubes, the deformation mode of the inner Al tube was found to be a more complex form of the diamond mode of deformation of empty Al tube, leading to higher crushing load values than the sum of the crushing load values of empty composite tube and empty metal tube.TÜBİTAK for the grant MİSAG-22

Experimental testing and full and homogenized numerical models of the low velocity and dynamic deformation of the trapezoidal aluminium corrugated core sandwich

The simulations of the low velocity and dynamic deformation of a multi-layer 1050-H14 Al trapezoidal zig-zag corrugated core sandwich were investigated using the homogenized models (solid models) of a single core layer (without face sheets). In the first part of the study, the LS-DYNA MAT-26 material model parameters of a single core layer were developed through experimental and numerical compression tests on the single core layer. In the second part, the fidelities of the developed numerical models were checked by the split-Hopkinson pressure bar direct impact, low velocity compression and indentation and projectile impact tests. The results indicated that the element size had a significant effect on the initial peak and post-peak stresses of the homogenized models of the direct impact testing of the single-layer corrugated sandwich. This was attributed to the lack of the inertial effects in the homogenized models, which resulted in reduced initial peak stresses as compared with the full model and experiment. However, the homogenized models based on the experimental stress–strain curve of the single core layer predicted the low velocity compression and indentation and projectile impact tests of the multi-layer corrugated sandwich with an acceptable accuracy and reduced the computational time of the models significantly

The effect of tube end constraining on the axial crushing behavior of an aluminum tube

The effect of various types of end constraining on the deformation and load-displacement behavior of a 3003-H14 Al tube were experimentally and numerically studied. No effect of single-end constraining of tubes was found. Few conditions of double-end constraining tended to revert the deformation mode to mixed and/or diamond mode of deformation. Double-end constraining of tube ends further resulted in an increase in initial drop-load values, widening the initial overshot region in average load-displacement curves. The agreement between numerical and experimental results showed the capabilities of the used numerical model in order to predict end-condition effects in tubular structures

Experimental and numerical investigation of the effect of interlayer on the damage formation in a ceramic/composite armor at a low projectile velocity

The damage formation in a multilayered armor system without and with an interlayer (rubber, Teflon, and aluminum foam) between the front face ceramic layer and the composite backing plate were investigated experimentally and numerically. The projectile impact tests were performed in a low-velocity projectile impact test system and the numerical studies were implemented using the nonlinear finite element code LS-DYNA. The results of numerical simulations showed that the stress wave transmission to the composite backing plate decreased significantly in Teflon and foam interlayer armor configurations. Similar to without interlayer configuration, the rubber interlayer configuration led to the passage of relatively high stress waves to the composite backing plate. This was mainly attributed to the increased rubber interlayer impedance during the impact event. The numerical results of reduced stress wave transmission to the backing plate and the increased damage formation in the ceramic front face layer with the use of Teflon and foam interlayer was further confirmed experimentally.Scientific and Technical Council of Turkey (106M353

Development of novel multilayer materials for impact applications: A combined numerical and experimental approach

A well-verified and validated numerical model was used to investigate stress wave propagation in a multilayer material subjected to impact loading. The baseline material consisted of a ceramic faceplate and composite backing plate separated by a rubber or teflon foam interlayer: several variants were investigated in which the number, type, and total thicknesses of the interlayers were altered. Comparison of the variants showed that the use of multiple teflon foam interlayers could drastically reduce the average stress in the multilayer material. Based on the numerical results, further experimental work was undertaken upon one of the variants. Very large and unexpected tensile stress oscillations were observed in the ceramic layers, leading to a refinement of the numerical model which successfully reproduced the oscillations and also demonstrated that separation of the sample layers led to trapping of the stress wave within the layers. Use of the validated numerical model allowed detailed analysis of the processes of wave transmission and demonstrates the important synergy that can exist between experimental and modeling studies. The current study provides a valuable starting point for designing future multilayer materials with specific, controlled properties

The effects of plastic deformation on stress wave propagation in multi-layer materials

The behavior of a multi-layer material at high strain rate and the effect of plastic deformation on stress wave propagation were investigated by a combination of experimental and numerical techniques. Plastic deformation effects were studied in multi-layer materials consisting of ceramic, copper and aluminum subjected to large strains under high strain rate loading. First, stress wave propagation behavior for the monolithic metals was studied, and then extended to multilayer combinations of these metals with each other and with a ceramic layer. The axial stress distributions were found to be non-uniform in the elastic deformation range of the specimen. The degree of non-uniformity was much more pronounced in the multi-layer samples consisting of different materials. The presence of a ceramic layer increased the magnitudes of stress gradients at the interfaces. It was also found that a major effect of plastic deformation is a tendency to produce a more homogeneous stress distribution within the components. The implications of these observations for practical systems are discussed.Army Research Office under Contract Number 47335-EG and National Science Foundation under Grant INT-024277