Instrumented Falling Weight Impact Tests Research Articles

Impact damage resistance of Jute/Kevlar hybrid composite laminates subjected to varying heights: An experimental approach

This work shows the after effects of a trial examination concerning the low-velocity impact response of Jute/Kevlar fiber epoxy hybrid composite laminates. Trial tests were executed according to ASTM principles utilizing an instrumented falling weight impact testing machine. Impact tests were directed to portray the type and extent of the damages observed in laminate subjected to various impacting heights: 50 to 250 mm. The reaction of these laminates to drop-weight low velocity impact at energy levels ranging from 0.4 to 2.3 J was examined. At impact height of 250 mm, there is a calamitous failure of laminates. It was discovered that the laminates displayed two kinds of failure modes viz., crack initiation and perforation of the laminate.

Mechanical response of polycarbonate nanocomposites to high velocity impact

In this study, the mechanical responses of polycarbonate (PC) and PC/multi-walled carbon nanotubes (MWCNTs) to dynamic loadings at low and high velocities impacts were investigated experimentally using an instrumented falling weight impact tester (IFWIT) and a split Hopkinson pressure bar (SHPB), respectively. The results from the IFWIT tests revealed that impact strength, impact failure energy and fracture toughness were dramatically enhanced by the incorporation of a very small amount of the MWCNTs into the PC matrix. The maximum load and the impact failure energy increased by ∼320% and ∼350%, respectively, when only 1wt% MWCNTs was incorporated. The results from the SHPB tests demonstrate that all the materials showed strain-rate sensitivity. The MWCNTs nanocomposites exhibited higher yield stress and energy absorption characteristics compared to the PC matrix material. However, the enhancement by MWCNTs was very limited for the PC containing higher percentage of the filler at higher strain rates. This could be resulted by a thermal-softening effect. In addition, the density of the pure PC and PC/MWCNTs nanocomposite specimens before or after SHPB testing was examined to gain insight into the microstructure changes. The results show that the density decreased significantly after the SPBH tests. With increasing strain rate the density decrease in PC nanocomposite is faster than that in the pure PC. It is believed that more cracks formed in the PC nanocomposite during the SHPB tests, which could result in high energy dissipation.

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.

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.

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.

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.

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.

Structure and properties of flax/polylactide/alumina nanocomposites

Composites composed of polylactide (PLA), woven flax fiber textiles (weave style of 2 × 2 twill and 4 × 4 hopsack) and boehmite alumina were produced by hot press. The spraying technique served for the pre-dispersion of the alumina nanoparticles. The aqueous alumina slurry was produced by mixing the water with water dispersible alumina. The dispersion of the flax structures and alumina particles in the composites was studied by scanning electron microscopy. The polylactide composites were subjected to water absorption and instrumented falling weight impact tests. The creep and thermomechanical properties of the composites were determined in short-time creep tests (performed at various temperatures), thermogravimetric analysis and dynamic-mechanical thermal analysis, respectively. It was found that the incorporation of alumina particles reduced the water uptake compared to the polylactide/flax blends. The impact energy and stiffness value of polylactide/flax blends was markedly higher than that of PLA but reflected the effects of composite structures. Incorporation of alumina particles enhanced storage modulus and the creep resistance compared to the polylactide/flax blends but slightly incremented thermal resistance at high temperature. No clear trend in the flax weave style-effect was found in the thermal behavior. The creep master curves were constructed by applying the time–temperature superposition principle. The Findley power law could satisfactorily describe the creep compliance versus time traces for all systems studied.

HDPE reinforced with nanoparticle, natural and animal fibers

Binary and ternary composites composed of high-density polyethylene (HDPE), boehmite alumina (BA) and different kinds of natural and animal fibers, such as flax, sponge gourd, palm and pig hair (PH), were produced by hot press technique. Aqueous BA suspensions were sprayed on the HDPE/flax mat to prepare nanoparticle/natural fiber–reinforced ternary polymer composites followed by drying. The dispersion of the natural and animal fibers and BA particles in the composites was studied by scanning electron microscopy and discussed. The thermomechanical and stress relaxation properties of the composites were determined by the thermogravimetric analysis, dynamic-mechanical thermal analysis and short-time stress relaxation tests (performed at various temperatures), respectively. The HDPE-based composites were subjected to water absorption and instrumented falling weight impact tests. It was found that all the composite systems increased the stiffness and stress relaxation and reduced the impact toughness. The stress relaxation modulus of natural and animal fiber composites was higher compared with that of the neat HDPE. This modulus increased greatly with incorporation of BA. The relaxation master curves were constructed by applying the time–temperature superposition principle. The inverse of Findley power law could be fairly applicable to describe the relaxation modulus versus time traces for all systems studied. Incorporation of BA particles enhanced the thermal resistance, which started to degrade at higher temperature compared with the HDPE/flax mat composite. The HDPE/flax mat/BA composite could reduce the water uptake.

Impact, thermal and mechanical properties of high density polyethylene/flax/SiO2 composites: Effect of flax reinforcing structures

Composites composed of high-density polyethylene, woven flax fiber textiles (flax weave style of 2 × 2 twill and 4 × 4 hopsack) and SiO2 were produced by hot press with nanospraying technique. The SiO2 slurries were sprayed on the woven flax fiber followed by drying. The related HDPE/woven flax fibers composites were prepared by hot press. The dispersion of SiO2 particles and flax in the composites was studied by scanning electron microscopy. The related high-density polyethylene based composites were subjected to instrumented falling weight impact test. The thermal resistance, stiffness and tensile strength properties of the composites were determined in thermogravimetric analysis, dynamic-mechanical thermal analysis and tensile tests, respectively. It was found that the impact energy and stiffness value of high-density polyethylene/flax composites was markedly higher than that of high-density polyethylene but reflect the effects of composite structures and flax content. Incorporation of SiO2 particles enhanced resistance to thermal degradation. It was established that the linear viscoelastic material principle are fairly applicable to convert from the modulus to the creep compliance results.

Low-velocity impact response of non-woven hemp fibre reinforced unsaturated polyester composites: Influence of impactor geometry and impact velocity

In this study, the influence of varying impactor geometries on the impact damage characteristics of hemp fibre reinforced unsaturated polyester composites were subjected to a low-velocity impact loading using an instrumented falling weight impact test setup. The three varying tup geometries: hemispherical, 30° and 90°, at four different impact velocity levels: 2.52m/s, 2.71m/s, 2.89m/s and 2.97m/s were assessed. The experimental results to investigate the influence of impactor geometry suggest that HFRUP composites were able to withstand higher loads when tested with hemispherical impactor and also absorbed more energy than that for 90° and 30° shaped tup geometry. The post impact damage patterns and failure mechanisms of impacted samples were further characterised by ultrasonic (UT) inspection. Impact induced damage characterised by scanning electron microscope (SEM) suggests that damage induced by the impact included a typical failure mechanisms showing matrix cracking, fibre breakage and fibre pullout. As the impact velocity increases the damage to back face of the laminate increased for laminates tested with a hemispherical impactor while it decreased to certain extent for laminates tested with 90° and 30° impactor geometries.

Effect of the impact conditions on the mechanical properties of injection‐molded parts

AbstractThis work focused on the study of the impact event on molded parts in the framework of automotive components. The influence of the impact conditions and processing parameters on the mechanical behavior of talc‐filled polypropylene specimens was analyzed. The specimens were lateral‐gate discs produced by injection molding, and the mechanical characterization was performed through instrumented falling weight impact tests concomitantly assisted with high‐speed videography. Results analyzed using the analysis of variance (ANOVA) method have shown that from the considered parameters, only the dart diameter and test temperature have significant influence on the falling weight impact properties. Higher dart diameter leads to higher peak force and peak energy results. Conversely, higher levels of test temperatures lead to lower values of peak force and peak energy. By means of high‐speed videography, a more brittle fracture was observed for experiments with higher levels of test velocity and dart diameter and lower levels of test temperature. The injection‐molding process conditions assessed in this study have an influence on the impact response of moldings, mainly on the deformation capabilities of the moldings. POLYM. ENG. SCI., 52:1845–1853, 2012. © 2012 Society of Plastics Engineers

Influence of physical aging on impact embrittlement of uPVC pipes

Most failures of unplasticised poly(vinyl chloride) (uPVC) pipes used in the Dutch gas distribution network originate from third party damage. Brittle pipes should therefore be replaced to ensure safe operation of the network. In this study, the relation between physical aging and embrittlement of uPVC is investigated using instrumented falling weight impact tests. The ductile to brittle transition temperature was first measured for a water pipe grade uPVC at different stages of aging. As a hypothesis, a critical stress criterion is proposed above which failure is brittle. The evolution of the ductile to brittle transition temperature that followed from the use of this hypothesis and a model for the polymer yield stress agrees qualitatively with the experimental data. A minor increase in transition temperature was observed for the water pipe grade with aging. Applying the same hypothesis to a uPVC gas pipe grade shows a more pronounced influence of physical aging.

Effect of Nanoclay in Epoxy-based Fibre-glass Composite Laminates subjected to Low Velocity Impact

This work presents the influence of nanoclay in epoxy-based fibre-glass composite laminates and its behaviour under low-velocity impact. Glass fibre reinforced in epoxy-clay nanocomposites were fabricated by hand lay-up method. Experimental test were performed according to ASTM standards using an instrumented falling weight impact testing machine. Impact test were conducted to characterize the type and extent of the damage observed for 0, 1, 3 and 5 percentage of nanocomposites as subjected to three different energy levels - 6.32, 12.63 and 18.95 J. The impact result shows that 1% and 3% nanoclay laminates sustained maximum load bearing capacity with higher energy absorption. The impact strength has been increased due to the presence of nanoclay in the epoxy matrix. Impact responses of the nanocomposites are compared with neat counterpart in terms of retardation, penetration and absorbed energy. An impact damage of the nanocomposites is analyzed by visual inspection method.

Dynamic Mechanical and Perforation Impact Behavior of All-PP Composites Containing Beta-Nucleated Random PP Copolymer as Matrix and Stretched PP Homopolymer Tape as Reinforcement: Effect of Draw Ratio of the Tape

Cross-ply all-polypropylene (PP) composite laminates were prepared by hot consolidation after tape winding combined with film stacking. Alpha (α) PP tapes of different draw ratios (DR = 8 and 12), produced by online extrusion stretching, served as reinforcements. Beta (β)-nucleated random PP copolymer, introduced in the form of a film, composed the matrix. The E-modulus of the PP tapes increased whereas their density decreased with increasing DR. The volume fraction of the reinforcement and the void content were estimated using optical microscopic images. The all-PP composites were subjected to dynamic mechanical thermal analysis, flexural, and instrumented falling weight impact tests. It was found that with increasing draw ratio of the α-PP tapes, the stiffness, strength, and perforation resistance of the composites were improved.

The Effect of Electron Irradiation on the Mechanical Properties of MWCNT/Carbon Fiber Reinforced Hybrid Nanocomposites

In our work carbon fiber/epoxy composite and multiwalled carbon nanotube/carbon fiber/epoxy hybrid nanocomposite laminates have been prepared by resin transfer moulding (RTM) technology. The specimens have been irradiated using a high energy electron gun with multiple doses. The effect of the electron irradiation has been characterized using three point bending, interlaminar shear and instrumented falling weight impact tests.

Low-velocity impact response of injection-moulded polypropylene plates – Part 2: Effects of moulding conditions, striker geometry, clamping, surface texture, weld line and paint

The low-velocity, low-energy impact response of a mineral and elastomer modified polypropylene was characterised by instrumented falling-weight impact testing of plates with annular clamping. Most of the impact tests were performed at −30 °C with incident impact velocities in the range 1.0–4.4 m/s, and with plate thicknesses in the range 2.0–3.9 mm. The following factors were investigated: moulding conditions (mould temperature, melt temperature, holding pressure), striker geometry, clamping, plate surface texture, melt flow weld lines and paint. The occurrence of brittle fracture was affected by all these factors, except the moulding conditions. Reducing the striker hemisphere diameter or changing to a flat striker induced brittle fracture. Removing the annular clamping led to a more brittle response. Plates with a weld line were more brittle than standard plates. The surface texture caused brittle fracture when the textured side was in tension under the striker. The paint induced brittle fracture at −30 °C, but no adverse effect of the paint was observed at 20 °C.

Low-velocity impact response of injection-moulded polypropylene plates – Part 1: Effects of plate thickness, impact velocity and temperature

The low-velocity, low-energy impact response of a mineral and elastomer modified polypropylene was characterised by instrumented falling-weight impact testing of plates with annular clamping. Different loading conditions were assessed by varying plate thickness (2–4 mm), incident impact velocity/energy (up to 4.4 ms −1/34 J) and temperature (−60 to 20 °C). Force-deflection curves and fracture patterns were categorised and analysed. The main trends can be explained in terms of 1) deformations spanning from small-strain bending to large-strain stretching, 2) fracture responses spanning from linear-elastic brittle to highly ductile, 3) process-induced anisotropy, and 4) friction effects. With the highest impact velocity used in this study, plates thinner than ∼2.5 mm fractured at both −30 and 20 °C, although with different mechanisms. A remarkable finding was that the central radial crack under the striker ran parallel to the (injection moulding) flow direction for the most brittle fractures (at low temperatures), while it ran perpendicular to the flow direction in other cases.

Experimental investigation of low-velocity impact characteristics of woven glass fiber epoxy matrix composite laminates of EP3 grade

This work presents the results of an experimental investigation concerning the low-velocity impact behavior of woven glass fiber epoxy matrix composite laminates. Experimental test were performed according to ASTM standards using an instrumented falling weight impact testing machine. Impact test were conducted to characterize the type and extent of the damage observed in laminate for range of thickness subjected to different impact velocities. Correlation of the residual indentation of the impacted specimens provides a criterion for the extent of the damage. As the impact energy was increased, the samples experienced one of two types of damages: a crack from the center of the laminate to the edge, or significant damage consisting of a dent localized in the region of impact. The history of relevant kinematical, dynamic and energetic quantities, both to synthesize the dependency of the energy parameters and force threshold values on the impact velocity are discussed.