Falling Weight Impact Tests Research Articles

Shock-absorbing capability of lightweight concrete utilizing volcanic pumice aggregate

Sediment disasters from concentrated heavy rains severely damage to civil life. Concrete check dams are widely used to mitigate disasters, however, sometimes such structures are damaged due to collision of boulders or fluid force of debris flow. Placing buffer material in front of concrete structure can be an effective solution. On the other hand, there exist abundantly unused natural resources such as volcanic ash, scoria and pumice in the mountain regions. They sometimes have become risks of debris flow. Utilization of these materials is hence useful for resource circulation as well as disaster prevention.In this study, shock-absorbing capability of lightweight concrete utilizing volcanic pumice as coarse aggregate was experimentally investigated, for application to buffer material. In the impact test, a falling weight impact tester was employed, with placing buffer layer concrete on base layer concrete. Type of coarse aggregate, water-to-cement ratio, thickness of buffer layer and impact velocity were considered as experimental factors, and the experiments were designed with the Taguchi method. Sizes of specimens and levels of experimental factors were selected based on actual phenomena observed in sediment disasters. As a result, the lightweight concrete is proved to have a superior shock-absorbing capability than control concrete using crushed limestone as coarse aggregate. Statistical analysis results indicated that the lightweight concrete is by averages of 28% and 41% more effective in reducing the maximum impact load than the control concrete, under the impact velocities of 1.5m/s and 4.5m/s, respectively.

Effect of interfacial bonding on impact properties of chopped glass fiber polymer nanocomposites

This paper aims to presents the investigations made on the effect of impact response of chopped glass fiber–epoxy nanocomposite laminates subjected to low velocity impact using instrumented falling weight impact tests. The laminates were prepared using six layers of chopped strand mat with density of 610 gsm with epoxy resin and nanoclay content varied from 1, 3, and 5 wt%, by hand lay-up method. The nanoclay was dispersed into the epoxy by high shear mixing process in order to obtained uniform distribution of individual nanoclay. Laminates were impacted at constant mass with different impact energies. During these low velocity impact tests, the maximum load, absorbed energy, and deflection at peak load were recorded. It was observed that by dispersion of nanoclay as reinforcement, there was significant improvement in load carrying capacity and energy absorption. When a small amount of nanoclay (1 wt%) was added into the epoxy, the maximum load was enhanced by 20%. The presence of stiffer nanoclay significantly reduced the surface cracks propagation and controlled delamination area. Scanning electron microscopy was performed to characterize the damage progression.

Penetration impact resistance of novel tough steel fibre-reinforced polymer composites

Conventional composites are susceptible to impact loading due to their low toughness. Novel annealed steel fibres possess a unique combination of high stiffness and high strain to failure. A range of composite laminates incorporating various steel fibre architectures with thermoplastic and thermoset matrices were produced and the low-velocity penetration impact resistance was characterized by falling weight impact tests, showing the high potential toughness of steel fibre composites. The effect of different parameters was determined. High matrix strain to failure allows a better exploitation of the steel fibre ductility. The higher absorbed energy up to penetration, in case of laminates with lower levels of fibre/matrix adhesion is attributed to fibre debonding, potential for more plastic deformation, and pull-out mechanisms. Thinner fibres are more sensitive to premature failure due to inclusions in the steel fibres. Cross-ply laminates show higher energy absorption, probably due to increased delamination, whereas woven fibre structures lead to more localized damage. A preliminary study shows that layer by layer (‘macro’) hybridization of carbon and steel fabrics leads to penetration impact resistance close to the pure steel fibre composite, in case the steel plies are placed on the outside surfaces, showing a significant positive effect of hybridization.

OS1328-147 衝撃荷重によるCFRP積層板およびCFRPサンドイッチパネルの損傷評価と材料特性変化

In the present paper, damage development within carbon fiber reinforced plastic (CFRP) laminates and CFRP/Al honeycomb core sandwich panels by impact loading was evaluated, and change in material properties due to the damage development was investigated. Falling weight impact tests, cross section observation and 3-point bending tests were carried out. As results, it is obtained that reduction rate of bending elastic modulus in a laminate is lower than that in an upper face-sheet of the sandwich panel, and difference in the reduction rate between them becomes maximum at 5.1J. As a result of investigating the relationship between reduction in bending elastic modulus and internal damage development, the reduction is caused by delamination mainly. Since total length of cracks in CFRP/Al core sandwich panels is smaller than that in laminates, the sandwich panels have high impact tolerance.

Falling-weight impact tests of flexurally reinforced T-shaped PC beams with AFRP sheet

Falling-weight impact tests of flexurally reinforced T-shaped PC beams with AFRP sheet

Impact performance prediction of injection-molded talc-filled polypropylene through thermomechanical environment assessment

Due to the fact that different injection molding conditions tailor the mechanical response of the thermoplastic material, such effect must be considered earlier in the product development process. The existing approaches implemented in different commercial software solutions are very limited in their capabilities to estimate the influence of processing conditions on the mechanical properties. Thus, the accuracy of predictive simulations could be improved. In this study, we demonstrate how to establish straightforward processing-impact property relationships of talc-filled injection-molded polypropylene disc-shaped parts by assessing the thermomechanical environment (TME). To investigate the relationship between impact properties and the key operative variables (flow rate, melt and mold temperature, and holding pressure), the design of experiments approach was applied to systematically vary the TME of molded samples. The TME is characterized on computer flow simulation outputs and defined by two thermomechanical indices (TMI): the cooling index (CI; associated to the core features) and the thermo-stress index (TSI; related to the skin features). The TMI methodology coupled to an integrated simulation program has been developed as a tool to predict the impact response. The dynamic impact properties (peak force, peak energy, and puncture energy) were evaluated using instrumented falling weight impact tests and were all found to be similarly affected by the imposed TME. The most important molding parameters affecting the impact properties were found to be the processing temperatures (melt and mold). CI revealed greater importance for the impact response than TSI. The developed integrative tool provided truthful predictions for the envisaged impact properties.

Penetration impact testing of self-reinforced composites

Penetration impact resistance is one of the key advantages of self-reinforced composites. This is typically measured using the same setup as for brittle fibre composites. However, issues with the test configuration for falling weight impact tests are reported. Similar issues have been found in literature for other composites incorporating ductile fibres. If the dimensions of the test samples are too small relative to the clamping device, then the test samples can heavily deform by wrinkling and necking. These unwanted mechanisms should be avoided as they absorb additional energy compared to properly tested samples. Furthermore, these mechanisms are found to occur more easily at lower compaction temperatures due to the lower interlayer bonding. In conclusions, the sample dimensions of ductile fibre composites should be carefully selected for penetration impact testing. If wrinkling or necking is observed, then the sample dimensions need to be increased.

Erratum to: Mechanical and Impact Properties of PLA/2 × 2 Twill and 4 × 4 Hopsack Weave Flax Textile Composites Produced by the Interval Hot Pressing Technique

Polylactide (PLA)/2 × 2 twill and 4 × 4 hopsack weave flax textile composites were produced by the interval hot pressing technique. The dispersion of structural elements of the composites was inspected by the scanning electron microscopy (SEM). The composites were subjected to instrumented falling-weight impact tests. Their mechanical properties (tensile strength and stiffness) were determined in tensile and dynamic mechanical thermal tests. The SEM showed that the interfacial gaps around pulled-out fibers diminished when the interval hot pressing was used. It was also found that both the types of flax composites had a higher impact resistance than the neat PLA. The tensile strength and stiffness of the PLA/flax composites were also markedly higher than those of PLA and reflected the effect of their structures. The storage creep compliance was determined by using the relations of linear viscoelastic materials and the time-temperature superposition principle. The calculated creep response of the flax composites was much lower than that of the neat PLA.

Resistance to impact of cross-linked denture base biopolymer materials: Effect of relining, glass flakes reinforcement and cyclic loading

AimsThe effect of reinforcement and cyclic loading on the resistance to impact (RI) of denture base biopolymer materials was evaluated using Charpy (C) and falling-weight (FW) impact tests. MethodsBar-shaped (60×6×2mm3) and denture-shaped specimens (2mm) for the C and FD tests, respectively, were prepared with Lucitone 550 (L) and Vipi Wave (V) and relined (2mm) using the same material or the autopolymerizing relining resins Tokuyama Rebase II (T) and Ufi Gel Hard (U). Bulk specimens (60×6×4mm3) of all materials (L, V, T and U) were also prepared and tested. To evaluate the effect of reinforcement, glass flakes were added to the powder of the relining resins T and U (5% by weight). Half of bar-shaped (n=320) and half of the denture-shaped specimens (n=480) were subjected to cyclic loading (10,000 cycles) before the impact tests. ResultsData were analyzed by one-way ANOVAs (α=0.05) and revealed that the RI of L and V were comparable and higher than those of U and T. Compared to L and V, the RI was increased by relining with T and decreased by relining with U. When relining was made using the same material (L and V) the RI was maintained. Flexural cyclic loading and the incorporation of glass flakes into the resins T and U did not cause any significant alteration in the RI. A high correlation between results from C and FW tests was observed (r=0.8854). ConclusionRelining may exert effects on the RI of L and V denture base resins, which vary according to the relining material used. The high correlation between C and FW, suggests that the Charpy test, using bar-shaped specimens, can be a simple and reliable method for evaluating factors that may influence the RI of denture base polymers.

Reinforced Flax Mat/Modified Polylactide (PLA) Composites: Impact, Thermal, and Mechanical Properties

Polylactide (PLA)/flax mat and modified PLA/flax mat composites were produced by the hot pressing technique. The dispersion of the flax mat in the composites was studied by the scanning electron microscopy (SEM). The PLA composites were subjected to an instrumented falling-weight impact test. The mechanical and thermal properties of the composites were determined by using tensile tests, a thermogravimetric analysis (TGA), and a dynamic-mechanical thermal analysis (DMTA). It was found that the flat mat increased the impact resistance of PLA, but the tensile strength of the modified PLA/flax mat composite decreased slightly compared with that of PLA. Data on the elongation at break pointed to a higher ductility of the modified PLA and its composites. Moreover, the addition of a thermal modifier enhanced the thermal resistance below the processing temperature of PLA and had a marginal effect on its glass-transition temperature. The master curves of the storage modulus were constructed by employing the time-temperature superposition (TTS) principle. The principle of a linear viscoelastic material was fairly applicable to transition from the modulus to the creep compliance for all the systems studied.

Polyethylene and polypropylene hybrid composites based on nano silicon dioxide and different flax structures

Hybrid composites composed of polypropylene (PP) or high-density polyethylene (HDPE), different flax fibers (unidirectional, biaxial, and twill2 × 2), and silicon dioxide (SiO2) were produced by hot-press technique. The ternary polymer composite was effectively fabricated by spraying SiO2 solvents onto the surface of flax fiber. The dispersion of SiO2 particles and flax in the composites was studied by scanning electron microscopy. The related PP- and HDPE-based composites were subjected to instrumented falling weight impact test. The thermal and mechanical properties of the composites were determined by thermogravimetric analysis, dynamic mechanical thermal analysis, creep and stress relaxation tests, respectively. It was found that thermal decomposition temperature of the PP or HDPE/flax composites increased by the addition of SiO2 particles. The impact energy, stiffness, creep resistance, and relaxation modulus value of all flax composites increased markedly compared with the PP and HDPE matrix. Time–temperature superposition was applied to estimate the creep and relaxation modulus of the composites as a function of time in the form of a master curve. The activation energies for all the PP and HDPE composites systems studied were also calculated using the Arrhenius equation. The generalized Maxwell model was fairly applicable to the stress relaxation results.

Low Velocity Impact Damage in Composite Laminates Based on Waste Polyolefins

Abstract Composite laminates based on polyolefin wastes coming from two different sources are compared with similar systems involving a virgin polypropylene in terms of damage behavior. In particular, this paper reports the response of film-stacked composite laminate plates subjected to falling weight impact tests. As expected, samples based on recycled polyolefins show lower impact parameters with respect to the latter ones even if a partial improvement of the performances can be obtained by modification of the matrix by an adequate coupling agent. Despite the inferior impact behavior, potential uses of new systems provide an opportunity to develop valuable products by reducing the environmental impact of plastic wastes.

The effect of needleless electrospun nanofibrous interleaves on mechanical properties of carbon fabrics/epoxy laminates

The effect of polyacrylonitrile nanofibrous interlaminar layers on the impact properties of unidirectional and woven carbon fabric (CF)-reinforced epoxy (EP) matrix composites was investigated. The nanofibers were produced directly on the surface of carbon fabrics by a needleless electrospinning method, and composites were then prepared by vacuum-assisted impregnation. Interlaminar shear stress tests, three-point bending, Charpy-impact and instrumented falling weight tests were carried out. The fracture surfaces were analyzed by scanning electron microscopy. Due to the nano-sized reinforcements, the interlaminar shear strength of the woven and unidirectional fiber-reinforced composites was enhanced by 7 and 11%, respectively. In the case of the falling weight impact tests carried out on woven reinforced composites, the nanofibers increased the absorbed energy to maximum force by 64% compared to that measured for the neat composite. The Charpy impact tests indicated that the nanofiber interleaves also led to a significant increase in the initiation and total break energies. Based on the results, it can be concluded that the presence of nanofibers can effectively increase the impact properties of composites without compromising their in-plane properties because the thickness of the composites was not altered by the presence of interleaves. The improvement of the impact properties can be explained by the good load distri- bution behavior of the nanofibers.

A consideration on sectional design of full-scale RC rock-shed model for falling-weight impact test

A consideration on sectional design of full-scale RC rock-shed model for falling-weight impact test

Falling-weight impact test of absorbing system models with soil cement and impact response analysis for full-scale rockfall protection walls

Falling-weight impact test of absorbing system models with soil cement and impact response analysis for full-scale rockfall protection walls

Large-scale falling-weight impact test of sand cushion and gravel cushion with various conditions

Large-scale falling-weight impact test of sand cushion and gravel cushion with various conditions

Impact fracture behaviour of silane-treated halloysite nanotubes-reinforced unsaturated polyester

This work investigates the effects of untreated and silane-treated halloysite nanotube (HNT) particles on the micromechanism of plastic deformation of unsaturated polyester (UP) nanocomposites under impact loading conditions. The impact fracture properties of the prepared materials were characterised based on the temperature range of −20 to +60°C using falling weight impact tester. The chemically-modified halloysite with silane coupling agent (s-HNT) showed less hydrophilic towards the polyester matrix, thereby a good interfacial adhesion and uniform structures of HNT in the matrix are obtained compared to the untreated. The incorporation of both unmodified and modified HNT particles up to 5wt.% into the UP revealed a modest increase in the impact strength and total energy of nanocomposites, since the well dispersed particles in the matrix hindered the crack propagation under the impact loading. SEM examinations revealed that the fracture mode on UP surface was a smooth fast brittle while, the nanocomposite surfaces showed a sign of plastic deformation.

Experimental characterization and computational simulations of the low-velocity impact behaviour of polypropylene

Fil: Torres, Juan Pablo. Consejo Nacional de Investigaciones Cientificas y Tecnicas. Centro Cientifico Tecnologico Mar del Plata. Instituto de Investigacion en Ciencia y Tecnologia de Materiales (i); Argentina; Universidad Nacional de Mar del Plata. Facultad de Ingenieria; Argentina;

Effect of woven flax structures on morphology and properties of reinforced modified polylactide composites

Composites composed of polylactide (PLA), modified PLA and woven flax fiber textiles (flax weave style of 2 × 2 twill and 4 × 4 hopsack) were produced by hot press technique. Two structurally different additives were used to modify PLA. The dispersion of the flax in the composites was studied by scanning electron microscopy and computed microtomography system (µCT). The PLA composites were subjected to water absorption and instrumented falling weight impact tests. The thermomechanical and creep properties of the composites were determined using thermogravimetric analysis, dynamic-mechanical thermal analysis and short-time creep tests. It was found that the modified PLA and its composite increased the impact resistance compared with the unmodified PLA. Incorporation of flax decreased resistance to thermal degradation and increased water uptake. The impact energy and stiffness value of PLA/flax composites were markedly higher than that of PLA but reflect the effects of composite structures and flax content. The storage modulus master curves were constructed by applying the time–temperature superposition principle. From the master curve data, the effect of modified PLA on the storage modulus was more pronounced in the low frequency range.

Development and characterisation of injection moulded, all-polypropylene composites

In this work, all-polypropylene composites (all-PP composites) were manufactured by injection moulding. Prior to injection moulding, pre-impregnated pellets were prepared by a three-step process (filament winding, compression moulding and pelletizing). A highly oriented polypropylene multifilament was used as the reinforcement material, and a random polypropylene copolymer (with ethylene) was used as the matrix material. Plaque specimens were injection moulded from the pellets with either a film gate or a fan gate. The compression moulded sheets and injection moulding plaques were characterised by shrinkage tests, static tensile tests, dynamic mechanical analysis and falling weight impact tests; the fibre distribution and fibre/matrix adhesion were analysed with light microscopy and scanning electron microscopy. The results showed that with increasing fibre content, both the yield stress and the perforation energy signifi- cantly increased. Of the two types of gates used, the fan gate caused the mechanical properties of the plaque specimens to become more homogeneous (i.e., the differences in behaviour parallel and perpendicular to the flow direction became neg- ligible).