Drop-weight Impact Response Research Articles

Effect of MWCNT Anchoring to Para-Aramid Fiber Surface on the Thermal, Mechanical, and Impact Properties of Para-Aramid Fabric-Reinforced Vinyl Ester Composites

In the present work, para-aramid fabrics (p-AF) were physically modified via an anchoring process of 0.05 wt% MWCNT to the aramid fiber surfaces by coating the MWCNT/phenolic/methanol mixture on p-AF, and then by thermally curing phenolic resin of 0.01 wt%. Para-aramid fabric-reinforced vinyl ester (p-AF/VE) composites were fabricated using p-AF/VE prepregs by compression molding. The effect of MWCNT anchoring on the thermo-dimensional, thermal deflection resistant, dynamic mechanical, mechanical, and impact properties and the energy absorption behavior of p-AF/VE composites was extensively investigated in terms of coefficient of linear thermal expansion, heat deflection temperature, storage modulus, tan δ, tensile, flexural, and Izod impact properties and a drop-weight impact response. The results well agreed with each other, supporting the improved properties of p-AF/VE composites, which were attributed to the effect of MWCNT anchoring performed on the aramid fiber surfaces.

Effect of cellulose and lignin content on the mechanical properties and drop-weight impact damage of injection-molded polypropylene-flax and -pine fiber composites.

Designing bio-composites for structural applications requires a thorough understanding of their mechanical behavior. In this study, we examined the differences in the tensile strength and drop-weight impact response between polypropylene reinforced with flax fibers and that reinforced with pinewood short fibers, as both fibers differ in composition (cellulose, hemicellulose, and lignin) and length-to-diameter ratio. We found that flax fibers, which have higher cellulose content and are twice as long as pine fibers, increased the stiffness and shock resistance of bio-composite materials. However, pine fibers, which contain more lignin, showed increased material ductility and energy absorption. Impulse excitation, acoustic emission and micro-CT techniques were used to evaluate the post-impact mechanical properties and the contribution of each damage mechanism to the final material failure (tearing). The experimental results were used to validate a model based on finite elements. Our results revealed that the experimental and finite-element analyses were in good agreement.

MECHANICAL PERFORMANCE OF CARBON - ARAMID FIBER-REINFORCED LAMINATED COMPOSITES UNDER IMPACT AND SHEAR LOADING

In this study, the drop weight impact response and the interlaminar shear strength of hybrid carbon/aramid fiber-reinforced laminated composites with different stacking sequences were investigated. Seven different laminates including two types of sandwich-like interply hybrid, three types of interply hybrid, and two types of non-hybrid named carbon and aramid were produced using the vacuum-assisted resin transfer molding method. Drop weight impact and short-beam shear tests were applied to the laminates to calculate the low-velocity impact response and the interlaminar shear strength, respectively. It is observed that while the outer layer of the hybrid structure is carbon, the structure can carry less load but absorb more energy. Pure carbon and pure aramid composites cannot carry loads but can absorb energy as much as their hybrid versions can. Sandwich-like interply hybrid with central carbon showed the best results when load and energy values were compared. Also, sandwich-like interply hybrid with central carbon has higher ILSS among hybrid structures because its center region consists of carbon layers.

FEM Analyses of Low Velocity Impact Response of Sandwich Composites with Nanoreinforced Polypropylene Core and Alu-minum Face Sheets

Sandwich composites with nanoreinforced polypropylene core and aluminum face sheets were studied under low velocity impact using a finite element model. A three dimensional quarter model was implemented to simulate the drop weight impact response of sandwich structures. In order to consider the strain rate dependent behavior of the core and face sheets, the Johnson–Cook material model was used for both of the polypropylene and aluminum layers. Effects of the different weight ratio of nanoparticles, the core thickness and the impactor mass were studied on the impact outputs. Comparing the impact responses of the sandwich structures with different weight ratio of nanoparticles revealed that positioning a polypropylene layer with 0.5% weight ratio of graphene as the core of sandwich panel caused the minimum amounts of damage area and transverse displacement. Adding more amount of nanoparticles did not improved the mechanical response of the sandwich structures. Increasing the impactor mass caused an increase of the contact force and the contact duration. Increasing the core thickness caused a decrease of the contact duration and increase of the contact force. The finite element outputs were well validated against the experimental results.

Low-velocity impact response of tube-reinforced honeycomb sandwich structure

To improve the load carrying capacity, structural stiffness, and impact resistance of a honeycomb sandwich structure, the honeycomb holes are filled with metallic tubes. Experimentally and numerically studies were carried out on the drop weight impact response of the tube-reinforced honeycomb sandwich structure. The results show that the stiffness and peak load of the honeycomb sandwich structure were increased by the metallic tube filler. The addition of tube filler made the Mises stress and deformation distribution of the front and back face-sheets more uniform. In addition, the tube-reinforced structure absorbed the impact energy more quickly than the empty honeycomb sandwich structure and the front face-sheet deformation was markedly reduced by tube reinforcement. The peak load and contact energy (the energy absorbed by the local deformation of sandwich structures) were predicted theoretically for both empty honeycomb sandwich structure and tube-reinforced honeycomb sandwich structure. The finite element parametric study shown that, compared with the empty honeycomb sandwich structure, the maximum deflections of the front and back face-sheets of the globally filled tube-reinforced honeycomb sandwich structure were reduced by 18.6% and 36.4% respectively. The tube-reinforced honeycomb sandwich structure is a promising structure for weight sensitive applications owing to its improved load carrying capacity and impact resistance.

A three-dimensional progressive damage model for drop-weight impact and compression after impact

In this paper, an enhanced three-dimensional continuum damage mechanics model is applied to predict the drop-weight impact response and compression after impact failure of a fiber-reinforced polymer composite specimen. The three-dimensional progressive damage model incorporates a three-dimensional maximum stress criterion to predict the intra-ply damage initiation, followed by a fracture-energy-based smeared crack model to capture the post-peak softening behavior. Driven by the dominant through-the-thickness failure under impact loading, a three-dimensional continuum damage model is implemented for the three-dimensional solid element via its explicit material model for Abaqus (VUMAT) to capture the effect of three-dimensional stress state and the interaction of matrix cracking and delamination. Abaqus’ restart analysis capability is used to activate the compression after impact analysis using the final damage state from the dynamic impact analysis. Both the dynamic failure and the compression after impact are demonstrated via a suite of verification examples followed by the sensitivity analysis using distinct impact configurations. The predictive capability of the proposed three-dimensional damage model is first verified using a static open-hole tension test. Applications of the damage model are then demonstrated for simulations of the dynamic drop-weight tests and compression after impact tests. A comparative study on the developed method is performed using the results predicted from the open-source CompDam. A sensitivity study is also performed to demonstrate the impact energy-dependent failure mode. The proposed model has shown its advantages in performing a quick assessment of impact damage and its effects on the residual compressive strength.

Impact behavior of hybrid composite plates dependent on curing and different stacking sequences

Abstract In this study, the drop weight impact response of cured hybrid composite plates has been investigated. Experiments were conducted on two groups of hybrid composite plates. The first group was based on upper and lower surfaces that are made of carbon (c) with the inner plates of glass (g), while for the second group the upper and lower surfaces were examined which are made of glass (g) with the inner plates of carbon (c). The orientation angle of the plates was 0, 15, 30 and 45° and the collision energy was 12 J. Contact forces were obtained and compared for the plates with respect to the different sequence and orientation angles. Peak forces increased for all the sequences and orientation angles. However, the (g-c-c-g) stacking sequence showed a larger sensitivity to an orientation angle change. The deflections decreased for the (c-g-g-c) stacking sequence when the orientation angle increased.

Flat nose low velocity drop-weight impact response of carbon fibre composites using non-destructive damage detection techniques

AbstractThis work is mainly concerned with the nondestructive post-impact damage evaluation of carbon fibre reinforced laminated composite panels subject to low velocity drop-weight impact by flat and round nose impactors. Quasi-isotropic laminates consisting of eight-, sixteen-, and twenty-four plies were impacted by flat and round nose impactors at different velocity levels. Load-time history data were recorded and plotted to correlate loaddrop as damage level to the impactor nose profiles. Test produced data, non-destructive damage detection techniques: visual, ultrasonic, and eddy- current, and computer simulations were utilised to identify and quantify status of the impact induced damage. To evaluate damage in relatively thick laminates (consisting of 24-Ply), the damage ratios and deflection quantities were correlated to the corresponding impactor nose profiles. Damage induced by the flat nose impactor to thick laminates was compared against the data produced by the round nose impactor. Results show that relatively thin laminates were largely affected by the impactor nose. Reasonable difference was observed in damage caused by flat and round impactor nose profiles to thick laminates impacted at relatively higher velocity impacts. Resultswere compared and validated against simulation produced data.

Effects of interply hybridization on the damage resistance and tolerance of composite laminates

This paper presents an experimental study of the drop-weight impact response of interply hybrid laminates manufactured using polymer-matrix composite materials. Three different reinforcements, woven carbon fabric, woven glass fabric and unidirectional carbon tape, are combined with an epoxy resin using the Resin Transfer Molding (RTM) process. In-plane quasi-isotropic laminates are analyzed by combining pairs of materials and by changing their location in the through-the-thickness direction of the laminate. In addition, different impact configurations defined in terms of impact energy are performed to increase the number of case studies. The analysis is completed by non-destructive inspections based on ultrasonic technique and Compression After Impact (CAI) tests for the assessment of the residual strength. The results obtained highlight the effects of interply carbon and glass hybridization under low-velocity impact and CAI loading.

Drop-weight impact response of hybrid composites impacted by impactor of various geometries

Drop-weight impact response of hybrid woven composite plates was studied. Hybrid S2 glass-IM7 graphite fibers/toughened epoxy composites with two lay-up arrangements were impacted using spherical, flat-ended cylindrical and straight-line Charpy impactors. The time-histories of impact-induced dynamic strains and impact forces were recorded. The damaged specimens were inspected using ultrasonic C-Scan methods. Experimental results exhibited that hybrid composites with glass outer skins had higher resistance to impact compared to second type. It also delaminated more than hybrid composites with graphite outer skins. The 3-D dynamic finite element software, LS-DYNA, was then used to simulate the experimental result of drop-weight tests. Good agreement between experimental and FE results was achieved when comparing dynamic force, strain histories and damage patterns between experimental measurements and finite element simulations.

Drop-Weight Impact Response of Fibre Reinforced Cement Based Foams

This paper describes the strength and toughness of fibre reinforced cement based foams subjected to bending under variable strain rates. Drop-weight impact tests were conducted on notched beams with cast density between 475 kg/m3 to 1200 kg/m3. The foams were reinforced with 0–0.2% polypropylene microfibre by volume and their role in improving the dynamic properties is illustrated. The structure of the cell wall within the foams was engineered through a suitable choice of foaming agent, such that foams with a predominantly closed cell structure were produced. Companion tests were conducted as per ASTM standards in compression and flexure under quasi-static loading. The results were compared to other brittle cellular solids from the literature, and the mechanical properties are described in terms of the relative density, defined as the ratio of the density of the cellular composite relative to that of Portland cement paste in the cell wall. The study shows that under quasi-static loading, the compressive strength, elastic modulus and modulus of rupture of plain mixes scale with the square of the relative density. On the other hand, the flexural toughness factor scaled linearly with it. Fibres were seen to increase the flexural strength at all rates of loading, regardless of cast density. However, the Poisson's ratio remained unaffected by the density of the mix. Further, cement based foams were seen to be strain rate sensitive but, the existing CEB-FIP model for cementitious materials vastly overestimates the dynamic impact factor at lower cast densities.

Shock loading and drop weight impact response of glass reinforced polymer composites

Abstract Response of E-glass reinforced vinyl ester and urethane panels of varying structures subjected to shock loading and drop weight impact loading have been studied. Shock waves are created using a shock tube with a testing range of 3.08–7.53 MPa peak incident pressure. The materials performance under shock loading was evaluated by post-mortem visual damage assessment, residual compressive strength, and permanent deformation mapping of the panels. Drop weight impact performance was measured by energy absorbed by the samples, depth of penetration, and extent of internal damage. Glass preforms having total areal weights 144 and 216 oz / yd 2 (4.88 and 7.32 kg / m 2 ) were infused with either one of three separate types of vinyl ester and one urethane resin. The results show that urethane panels having total glass preform areal weight of 216 oz / yd 2 ( 7.32 kg / m 2 ) performed better than similar vinyl ester resin panels. It was also found that of two materials with identical vinyl ester resins having total preform areal weight of 144 oz / yd 2 ( 4.88 kg / m 2 ) , the one with a finer glass structure consistently performed better in all evaluation criteria for shock wave and drop weight impact testing.

High-speed photographic study of the drop-weight impact response of RDX/DOS mixtures

This paper describes dropweight experiments performed on conventional and ultrafine cyclotrimethylene trinitramine (RDX) to which was added various percentages of the binder dioctyl sebacate (DOS). The ultrafine material particle size was less than 1 μm, while the conventional was 400 μm. The first aim of these experiments was to investigate the effect on the deformation, ignition behavior and impact sensitivity when DOS was added. A further aim was to determine possible sources of ignition in this energetic system. Techniques used included optical microscopy, heat sensitive film, and high-speed photography. The DOS was found to coat the individual particles of RDX. However, under impact loading, the DOS produced a blocky texture of millimeter dimensions. When ignition took place, the primary mechanism was localized adiabatic shear banding.

High-speed photographic study of the drop-weight impact response of ultrafine and conventional PETN and RDX

This paper describes a series of drop-weight experiments performed on pentaerythritol tetranitrate (PETN) and cyclotrimethylene trinitramine (RDX). Both chemicals were available in a conventional grain size (10–200 μm for PETN, 30–500 μm for RDX) and in a novel ultrafine particle size (<1 μm). The aim of the study was to determine the relative sensitivity of the four materials and to investigate the mechanisms by which ignition occurred in the samples. Heat sensitive film and high-speed photography revealed adiabatic shear bands in all four materials. However, trapped gas appeared to be the main reason for ignition. Because ultrafine powders have smaller interstices between grains, this could explain why the ultrafine samples were less susceptible to drop-weight impact.

Interpretation of signals from dropweight impact tests

A spring-mass model has been developed to describe the dropweight impact response of CFRP panels. The model separates the effects of the main impact impulse, high frequency oscillations and free vibrations and can be used as a reliable guide for effective digital filtering of signals from dropweight impact tests. Whilst the model at present does not account for damage, the onset of high frequencies towards the peak impact force indicate the onset of damage in the panel. The oscillations become larger and extend over a wider plateau as the perforation threshold energy is approached.

Effect of interleaving on the impact response of a unidirectional carbon/epoxy composite

Instrumented drop-weight impact response of a unidirectional carbon/epoxy composite and that of the corresponding laminate interleaved with poly(ethylene- co-acrylic acid) at the midplane were studied. The impact penetration energy of the unidirectional composite beam increased strongly upon interleaving. Realtime observations using a microscope in a static flexure test indicated a dramatic change of failure mode from the dominantly compressive fracture of the baseline laminate to the dominantly tensile fracture process upon interleaving, in accordance with the corresponding fractographic features of the impact specimens. These observations were attributed to the change in stress distribution upon introduction of the interleaf layer. The relevance of the present observations to the role of high-strain, low-modulus adhesive layers in the toughening of composites is discussed.