Perforation Threshold Research Articles

Recycled PET foam core sandwich panels with reinforced hybrid composite facesheets: A sustainable approach for enhanced impact resistance

This research explores the Low-Velocity Impact behavior of thermoplastic composite sandwich panels with 100% recycled Polyethylene Terephthalate (PET) foam sourced from post-consumer plastic water bottles. Being recognized as a reliable technique, hybridization using stainless-steel mesh layers was employed to reinforce the panels’ composite facesheets of sandwich panels accessible for modular housing, cold storage rooms and cargo trucks. Adequate impregnation of the reinforcement metallic mesh layer alongside proper skin-to-core adhesion was accomplished by optimizing a two-phase compression molding method. The effect of hybridization on impact response of sandwich panels with two different PET foam core thicknesses, and stacking sequence were evaluated. It was revealed that reinforcing the impacted surface of the composite sandwich panels significantly increased the perforation threshold. Moreover, analyzing the post-impact section view of the samples indicated that hybridization modified the damage propagation response of the PET foam core sandwich composites, through which the energy absorption capacity was improved.

Experimental investigation on the effects of stainless-steel mesh reinforcing layers on low-velocity impact response of hybrid thermoplastic glass fiber composites

This study aims to assess the hybridization effect on the perforation threshold of Low-Velocity Impact (LVI) in thermoplastic glass composite laminates, incorporating layers of resin-impregnated stainless-steel mesh. Reinforcing methodologies such as hybridization are recently being adopted as a practical approach to increasing the energy-absorbing capacity of polymer composites. In the current paper, a multi-step hot press lamination method has been employed to fabricate the hybrid composite laminates strengthened with stainless-steel mesh layers. Several stacking sequences, metal mesh wire sizes, orientation and position relative to the impactor have been examined under various LVI energies. It was revealed that the LVI penetration energy was increased for the thermoplastic-based composite laminates reinforced with stainless-steel mesh layers. Furthermore, the LVI penetration energy threshold was significantly influenced by the metal mesh wire size, orientation and stacking sequence. Finally, the backlight method capability was assessed to detect the after-impact interlaminar damages.

Effect of impactor nose form on the impact behavior of reinforced composite materials

Abstract The goal of the present study is to investigate the influence of impactor shape on the low-velocity impact behavior of the composite panels manufactured with different reinforcement materials at the same thicknesses, experimentally. Kevlar, carbon, S-2 glass woven fabric and epoxy matrix have been used to manufacture thermoset composites with the vacuum-assisted resin infusion molding method. The Fractovis plus test machine with a 12.7 mm diameter hemispherical and two different conical impactor noses was used to perform impact tests. The effects of impactor shapes on the low-velocity impact behavior have been compared for 20 J, 40 J, and 60 J energy levels. Although at the same impact energy level, S-2 glass fiber-reinforced epoxy specimens have a higher perforation threshold than carbon and Kevlar fiber-reinforced epoxy. Because to achieve the same thickness, the number of S-2 glass layers was greater than the number of carbon and Kevlar layers. Additionally, the form of the impactor greatly influenced the perforation threshold.

Low velocity impact behavior of twill basalt/epoxy composites modified by graphene nanoparticles

Nanoparticles are considered as feasible strengthening agent which strengthen different types of polymeric materials with minor reduction in the density of composites. In this study, 0.1 and 0.5 wt. % Graphene Nano Platelets (GNPs) are added to the matrix of basalt fiber reinforced epoxy composites (BECs) and the effects of such addition on low velocity impact behavior are investigated. In this regard, the epoxy matrix is reinforced in macro scale by basalt fibers weaved together in 2/2 Twill pattern. Vacuum Assisted Resin Infusion Molding (VARIM) method is used to fabricate the pure and multi-scale BECs. The profile energy method is also used to evaluate the penetration and perforation threshold of fabricated pure and multi-scale BEC specimens. The force versus time and deflection, energy and deflection versus time curves are plotted and the key parameters of low velocity impact test including maximum force, energy and deflection are compared. According to the results, introducing of GNP nanoparticles in the matrix of BECs improves the low velocity impact behavior of these composites by increasing the contact force and decreasing the absorbed energy in rebounding state. Finally, based on the experiments, the 0.5 wt.% BEC has the best impact performance by applying 15.08 kN impact force against the applied forces of 13.78 kN and 11.208 kN for 0.1 wt.% and pure BECs.

The influence of pin on the low-velocity impact performance of foam sandwich structure

In this study, experimental and computational approaches are used to explore the influence of relative position parameter (ratio of the axial distance between the impactor and the pin to the sum of their radius) and dimensional parameter (ratio of impactor diameter to pin diameter) of pin and impactor on foam core sandwich structure under the low-velocity impact. First, sandwiches with various specifications were subjected to low-velocity impact tests with an energy of 34 J. Then reinforcing effect of the pins and the specimen damage condition were thoroughly evaluated using finite element analysis (FEA). The findings revealed that the enhancement impact was substantial when position parameters were below a value of one and was negligible when position parameters were greater than three. In addition, the deformation and damage patterns of the pins gradually transitioned from crushing to large curvature bending, micro-buckling, and negligible deformation were observed with increasing values of position parameters. To establish the law associating position and dimensional parameters with impact performance (including maximum contact force, resistance to impact damage, perforation threshold energy and dent depth), experiments were designed by the central composite design (CCD) method and simulated through FEA. The analysis of variance revealed that the position parameter have higher significance on the maximum contact force, damage resistance and perforation threshold energy, while the dimensional parameter have higher significance on the dent depth. Finally, a parameter optimization design approach was proposed that increased the sandwich's perforation resistance and damage resistance.

An experimental study on the effects of introducing carbon nanotube on low velocity impact behavior of carbon/aramid fiber reinforced intra-ply hybrid composites

In this research, the addition effects of Multi Wall Carbon Nanotube (MWCNT) on low velocity impact behavior of Carbon/Aramid Fiber Reinforced (CAFRP) intra-ply hybrid composites were studied. In this regard, three types of pure, 0.1 wt.% and 0.5 wt.% introduced CAFRP intra-ply hybrid composites were fabricated by Vacuum Assisted Resin Infusion Molding (VARIM) method. The profile energy method was used to determine the penetration and perforation threshold. The main purpose of this research was to improve the impact behavior of CAFRP by addition of MWCNT to the matrix of these composites. The low velocity impact test was also carried out in 30, 50, 80 and 120 J energy values. The effect of addition MWCNTs in the matrix of composite was investigated by plotting force, absorbed energy and deflection vs. time and the key parameters of impact test such as maximum contact force, absorbed energy, deflection and duration time were compared for pure and multi scale CAFRP composited. According to the results, the addition of MWCNT improved the low velocity impact behavior of CAFRP intra-ply hybrid composites by not only increasing the toughness of epoxy matrix but also upgrade the adhesion of carbon fibers to the epoxy matrix. It was also found that fiber breakage, fiber pull out, matrix cracking, delamination and fiber matrix debonding were the most important failure modes in these types of tested composites.

Experimental investigation on low-velocity impact response of carbon/glass hybrid S-shaped foldcore sandwich structure

Hybrid composites offer an effective method of improving toughness and impact properties while reducing the cost of an advanced composite material. This paper aims at experimentally investigating the influences of impact energy, impact position and ply combination on the low-velocity impact responses of carbon/glass hybrid S-shaped foldcore sandwich structures. Carbon/glass hybrid S-shaped foldcore sandwich structures were manufactured using plain weave carbon fabrics and satin weave glass fabrics with epoxy resin. Low-velocity impact tests were carried out to study the impact behavior. The results show that the damage mode of the sandwich panel gradually changed from the local damage of the top face sheet and the foldcore to the complete penetration damage of the sandwich panel with the increase of the impact energy. And the node position has higher load carrying capacity, energy absorption capacity, and resistance to deformation compared with the base position. Although the initial load carrying capacity of carbon/glass hybrid sandwich panels is lower than that of the carbon fiber reinforced plastic (CFRP) sandwich panels, the addition of glass fabrics can improve energy absorption capacity and perforation threshold of CFRP sandwich panels.

Vol4 num4-12 Compression after impact test on woven CFRP laminates: the effect of ply clustering

One of the mayor threats for FRP is the out-of-plane loading conditions such as impacts, which produce interlaminar failures, among others, decreasing drastically the material's strengths in plane. Drop weight and compression after impacts tests have been selected as the standard methodology to evaluate laminate performance under impact loadings. The present work aims to reveal the influence of the material structure in woven laminate response under impact. To this end a complete set of experiments was designed using the actual ASTM standards (D7136/D7137), including the actual monitoring capabilities to address this problem. Composite coupons, made of AGP 280-5H carbon/Epoxy satin, were manufactured using three laminate configurations to analyze the effect of ply clustering [(+-45)/(0/90)]4S, [(+-45)2/(0/90)2]2S, and [(+-45)4/(0/90)4]S). Laminates have been subjected to low velocity impact using an INSTRON-CEAST Fractovis 6875 drop weight tower while compression test has been performed using a INSTRON 250 kN. Impact tests have been recorded with two high speed video-cameras (Photron SA-Z 2100K) configured at 20000 fps in order to analyze the plate behavior during the impact. In addition, a three dimensional high velocity digital image correlation (3D-HV-DIC) analysis has been done with the VIC-3D 7 system to measure the out of plane displacement and strains evolution. Also 3D-DIC analysis has been carried out for the CAI test to check the validity of the failure modes. It has been observed that the most clustered laminates increase the perforation threshold, while it decrease the residual strength of the material, due to damage spreading effect.

Low-velocity impact perforation response of titanium/composite laminates: analytical and experimental investigation

The low-velocity impact perforation behavior of fiber-metal laminates (FMLs) is evaluated by analytical modeling. Four different FML layups consisting of glass fiber/epoxy layers and titanium alloy Ti–6Al–4V sheets are fabricated, exhibiting the same thickness of total metal layers. The perforation behavior, threshold, and energy absorption mechanisms of FMLs are assessed using a mass-spring system. The results indicate that the elastic–plastic force history of FMLs up to maximum force predicted by both membrane and bending strain energy (M & B) and membrane strain energy only (M only) is found to be in good agreement with experiments, with M only matches closely than both M & B. The principal part of the total energy absorption of FMLs with both M & B and M only accounts for the energy absorption associated with global deformation of titanium and glass/epoxy layers, which is 67–71% and 65–69%, respectively. Here, a higher percentage of energy is absorbed by FML 4/3–0.3, succeeding by FMLs 3/2–0.3(O), 3/2–0.4, and 2/1–0.6. The predicted perforation threshold and overall energy absorption by various damage mechanisms of FMLs are in good comparison with experiments. The perforation response has also been predicted for aluminum-based FMLs, agreeing well with experiments. This insists on the robustness of the offered model. Also, the perforation resistance seems to be higher for titanium-based FMLs than aluminum-based FMLs. The overall energy absorption seems to be higher for titanium-based FMLs under low-velocity impact than high-velocity impact. This is also observed in the case of aluminum-based FMLs.

Low-velocity impact response of Kevlar/epoxy aluminum laminates

In this experimental study, the low-velocity impact behavior of aluminum–Kevlar laminates (ARALL) was investigated. ARALL composites were prepared in two different configurations as aluminum–Kevlar–aluminum (AKA) and Kevlar–aluminum–Kevlar (KAK). The aluminum alloy used in the preparation of the samples was supplied as 5754 series 2 mm thick plates. Kevlar fabrics were supplied in a weight of 300 g/m2 and in twill weave type. Laminated composites with Kevlar twill fabrics were made through hand lay-up followed by the compression-molding process. [K]4 composite laminates were obtained by curing Kevlar/epoxy laminates under 100°C and 7 bar pressure for 180 min. Then, samples of size 100 × 100 mm were cut from the plates with a water jet. The cut specimens were bound together with two-component adhesive. An Instron Dynatup 9250 HV impact test device was used for impact tests. The energy profiling method was used, which expresses the impact energy and the corresponding absorbed energy. The increasing impact energy was performed on the two configurations of ARALL composites until perforation occurred. The perforation threshold of AKA samples was approximately 70% higher than that of KAK samples.

Modulating impact resistance of flax epoxy composites with thermoplastic interfacial toughening

The application of natural flax fibre/epoxy composites is growing in the automotive sector due to their good stiffness and damping properties. However, the impact damage resistance of flax/epoxy composites is limited due to the brittle nature of both epoxy and flax fibres and strong fibre/matrix adhesion. Here, biobased thermoplastic cellulose acetate (CA) is deployed as a fibre treatment to alter the damage development of flax/epoxy composites subjected to low-velocity impact. The perforation threshold energy and the perforation energy of unmodified cross-ply composites increased respectively by 66% and 42% with CA-treated flax fibres. The CA-modification modestly decreased the transverse tensile strength and in-plane tensile shear strength of the composites. However, it altered the brittle nature of flax/epoxy laminates in quasi-static tests into ductile failure with clearly increased fibre–matrix debonding.

Effect of Harsh Environmental Conditions on the Impact Response of Carbon Composites with Filled Matrix by Cork Powder

Composites are used in a wide range of engineering applications, as a result, exposure to hostile environments is rather common and its mechanical properties degradation is unavoidable. It is necessary to have a complete understanding of the impact of hostile environments on mechanical performance, namely critical solicitations as low velocity impacts. Therefore, this work intends to analyse the low velocity impact response of a carbon fibre/epoxy composite, and a similar architecture with an epoxy matrix filled with cork, after immersion into different solutions: diesel, H2SO4, HCl, NaOH, distilled water, seawater, and seawater at 60 °C. These solutions significantly affected the impact properties. In this context, the maximum load, maximum displacement, and restored energy behaviour were studied to understand the influence of exposure time. It was possible to conclude that such impact parameters were significantly affected by the solutions, where the exposure time proved to be determinant. The benefits of cork on the perforation threshold were investigated, and this parameter increased when the epoxy matrix was filled with cork. Finally, cork filled epoxy laminates also show less variation in maximum load and recovered energy than carbon/epoxy laminates.

Effect of temperature on the low-velocity impact response of environmentally friendly cork sandwich structures

Impact events are common in every-day life and can severely compromise the integrity and reliability of high-performing structures such as sandwich composites that are widespread in different industrial fields. Considering their susceptibility to impact damage and the environmental issues connected with their exploitation of synthetic materials, the present work aims to propose a bio-based sandwich structure with an agglomerated cork core and a flax/basalt intraply fabric as skin reinforcement and to address its main weakness, i.e. its impact response. In-service properties are influenced by temperature, therefore the effect of high (60 °C) and low (−40°C) temperatures on the impact behavior of the proposed structures was investigated and a suitable comparison with traditional (polyvinyl chloride) (PVC) foams was provided. The results highlighted the embrittlement effect of decreasing temperature on the impact resistance of the sole cores and skins and of the overall structures with a reduction in the perforation energy that shifted, in the last case, from 50–60 J at – 40 °C up to more than 180 J at 60 °C. A maleic anhydride coupling agent in the skins hindered fundamental energy dissipation mechanisms such as matrix plasticization, determining a reduction in the perforation threshold of all composites. In particular, neat polypropylene (PP) skins displayed a perforation energy of 20 J higher than compatibilized (PPC) ones at 60 °C, while agglomerated cork sandwich structures at 60 °C were characterized by a perforation threshold higher of at least 50 J.

Quasi-static and low-velocity impact responses of polypropylene random copolymer composites with adjustable crystalline structures

Currently, the effect of cooling rates on mechanical properties of continuous glass fiber-reinforced isotactic polypropylene (CGF/iPP) composites cannot be well revealed, due to the imperfect impregnation containing voids, limited selection of crystalline structures (i.e., boundary defects and lamellae thickness) and impact energy. Moreover, compared to the polypropylene random copolymer (PPR) with toughness-rigidity balance, the brittleness of iPP and incompatibility of iPP/elastomer system also limit the further improvement of impact resistance. Furthermore, to date, the influence of cooling rates on mechanical properties of CGF/PPR composites has not been reported. Herein, we reveal the influence mechanism of multiple crystalline structures on quasi-static, and on low-velocity impact behavior of CGF/PPR composites based on perfect impregnation. Results show that the tensile strength and impact resistance under perforation threshold both increase first and then decrease with the increased cooling rate, while the impact resistance at non-perforation threshold gradually improves. Severe boundary defects mask the contribution of other crystalline structures, resulting in the lowest tensile strength. After overcoming boundary defects, the type of lamella is the most important factor for the effect of stress transfer. In the case of non-perforation damage, laminate with the smallest crystallinity and the widest size distribution only suffers from subcritical damage. The stiffness of amorphous area generated by the density of tie chains and chain entanglements becomes the decisive factor for improving impact resistance of laminate above perforation threshold. This work may pave the way for improving mechanical properties of thermoplastic composites via generating specific crystalline structures.

Experimental and finite element analysis of the impact response of agglomerated cork and its intraply hybrid flax/basalt sandwich structures

Sandwich structures are widespread in all the industrial applications where a high stiffness-to-weight ratio is required. Despite the unique bending performance, they feature two major drawbacks: the massive exploitation of synthetic materials and a strong susceptibility to impact damage. This work addresses both problems, investigating the puncture impact response of bio-based sandwich structures with an agglomerated cork core and intraply flax/basalt hybrid skins. A preliminary campaign of impacts was performed on three agglomerated corks with different densities and on three traditional polyvinyl(chloride) foams with comparable densities. Based upon the results obtained, one agglomerated cork (NL25) and one PVC foam (HP130) were selected to realize a finite element analysis (FEA) on the sole core and to produce the whole sandwich composites. FEA results show a good agreement with experimental ones ensuring a reliable prediction of cores dynamic response. The tests performed on sandwich structures proved the feasibility of agglomerated cork as an effective core, able to provide an improved damage tolerance to the structure. NL25 sandwiches impacted at 20–30 J showed a permanent indentation 60–67% lower than HP130 ones. The coupling agent in skins has a detrimental effect reducing composites perforation threshold from 80 to 60 J.

Laser perforation of polyethylene terephthalate/polyethylene laminated film for fresh produce packaging application

The polyethylene terephthalate/polyethylene laminated film was perforated using a carbon dioxide (CO2) laser emitted at an infrared wavelength of 10.2 μm. Pulse durations were varied from 3 to 200 μs, which corresponded to the fluence from 5.5 to 369.8 J/cm2. Laser perforation process was irradiated on either PET side or PE side. With the increase of fluence, the surface deformation was observed to create microhole formation. The perforation threshold to create a microhole on the PET side was 74.0 J/cm2 and that on the PE side was 92.5 J/cm2. The microhole area and volume loss increased with the increment of fluence. Noticeably, the laser perforation on the PET side used up to 50 % less energy than the perforation from the PE side to create the same size through-microhole. Oxygen transmission rate (OTR) and carbon dioxide transmission rate (CO2TR) of the laminated film with single microhole increased with increasing microhole area. For packaging application, mixed vegetable salad was packed in a plastic tray and heat-sealed with a microperforated top lidding film. The steady state level of gas composition of 10 %–13 % O2 and 8 %–10 % CO2 was achieved in all packages, except the one without perforation. Film with OTR and CO2TR of approximately 23,616 and 17,952 cm3/m2.d, respectively, was clearly shown to create modified atmosphere condition in the package that could keep the mixed salad fresh for 9 days at 8 °C.

Experimental investigation on damage and wave propagation of PVB laminated glazing structures under impact loading

Experimental investigation on the damage and wave propagation characteristics in PVB laminated glass panels subjected to impact loading was conducted. By applying different impact energies, the effect of two projectile configurations, a wooden post and steel ball, was studied. The effect of impact location was also investigated. The dynamic response of the panels was measured at different locations on the test panels using strain gauges. Damage and transient response and wave propagation characteristics of test panels were reported and compared. The results showed that flexural wave was the predominant wave in the response. In addition, in-plane compressive wave was also observed. It was also shown that while the projectile contact area affected the maximum transient response and crack propagation characteristics, it had a limited effect on the perforation threshold. For panels impacted at the corners, coupled strain waves were created by wave reflection processes when the waves reached the panel boundaries. Moreover, the impact velocity had a pronounced effect on peak strain and strain rates of test panels.

The efficacy of nanoclay loading in the medium velocity impact resistance of kenaf/PLA biocomposites

This work focused on investigating the efficacy of clay nanoparticles loading in the medium velocity impact resistance of kenaf/polylactic acid (PLA) biocomposites. Kenaf/PLA biocomposites with different nanoclay loadings of 0, 3, 5 and 7% by weight were fabricated and their medium velocity impact resistance tested on a gas gun. Results indicate that the addition of nanoclay in the biocomposites improved the medium velocity impact resistance of the biocomposites, specifically the perforation threshold limit, energy absorbed, crack and damage resistance. Improvements on these properties were thought to be due to enhancements brought about by the nanoclays on interfacial bonding and microstructural properties of the biocomposites revealed through scanning electron microscopy (SEM) and X-ray diffraction (XRD) analyses. The nanoclays reduced the micro-voids thereby improving bonding between PLA and kenaf fibres. SEM–EDX analysis detected silicon and aluminium elements which were from the nanoclays and the elemental maps showed that all the elements were uniformly distributed in all cases with good dispersion of the nanoclays. However, incidences of nanoclay agglomeration were observed at 7 wt% nanoclay content which had adverse effects on the biocomposites properties. Optimum results were achieved with 5 wt% nanoclay content, beyond which a reduction in the medium velocity impact resistance was observed. The perforation threshold, energy absorption capacity, resistance to damage and prevention of crack propagation increased by 41.9, 109, 26.5 and 28.9%, respectively, at the 5 wt% nanoclay content level. The study shows that the addition of nanoclay improves the impact properties of kenaf/PLA biocomposites within the medium velocity range. The novel nanoclay impregnated biocomposite material developed is suitable for applications where good impact properties are required.

Performance of Kenaf Non-woven Mat/PLA Biocomposites under Medium Velocity Impact

Focus on biofibre-reinforced biopolymer composites as sustainable alternatives to non-biodegradable composites in high-performance applications is increasing. This work focused on characterising the performance of kenaf non-woven mat/PLA biocomposites under medium velocity impact loads. Biocomposite laminates of different fibre contents were fabricated and then analysed for their resistance to medium velocity impact on a high speed gas gun. The perforation threshold limit was determined and impact-induced damages analysed using non-destructive techniques. Results showed that kenaf non-woven mat/PLA biocomposites have a perforation threshold limit of 26 m/s and doubling of fibre content improved the perforation threshold limit by 42.3 %. The impact damage resistance of kenaf non-woven mat/PLA biocomposites increased by 27.6 % when fibre content was doubled. The failure modes resembled that of some conventional fibre-reinforced composites. It was concluded that kenaf non-woven mat/PLA biocomposites have a potential to cushion against medium velocity impacts and hence could be good replacements for the non-biodegradable composites used for cushioning against secondary debris in the medium velocity range.

Thermoset powder coating wastes as filler in LDPE – Characterization of mechanical, thermal and morphological properties

In this study, three different electrostatic powder coating wastes of thermoset structure were used as fillers for low-density polyethylene (LDPE). The mechanical, thermal, and morphological properties of these composites materials are reported. The thermoset powder coating wastes were hydrolyzed using water and alcohol, and then 10%, 20%, and 30% by weight of the deactivated wastes were mixed with LDPE, first in a mechanical dry mixer, and subsequently homogenized by melt compounding in an extruder at about 160 °C. Standard tensile test bars and plate-shaped samples were produced from these homogeneous compounds by injection molding. The effects of adding hydrolyzed powder coating wastes on the properties of LDPE were determined by mechanical, thermal, and morphological tests. Tensile strength and perforation threshold of the sample filled with powder coating wastes decreased to some extent compared to un-filled sample. However, an increase in izod impact and bending strengths has been observed. The results of this investigation demonstrate that powder coating wastes with thermoset structure can be used as fillers in LDPE.