Short-beam Strength Research Articles

In-plane properties of an in-situ consolidated automated fiber placement thermoplastic composite

Automated fiber placement (AFP) has been employed to manufacture aerospace structures for decades, with a recent focus on thermoplastic composites (TPCs). The in-situ consolidation AFP of TPCs is pursued as an energy-efficient additive manufacturing (AM) approach for fabricating composite structures. This work compares the in-plane mechanical properties of in-situ consolidated coupons with those of compression molded counterparts to provide new insights into their failure mechanics and processing-structure relationships. Tensile and compressive properties along the fiber and transverse directions, in-plane shear properties, and short beam strength were measured for all samples. Failure modes and mechanics in tested coupons were related to AFP defects and processing, i.e., resultant crystallinities, fiber misalignment, matrix mechanical properties, porosity, and fiber–matrix interfacial strength. The findings of this study can be used to guide the manufacturing of future TPC structures and potentially open new avenues for applications where post-processing is not feasible or reduced mechanical performance is acceptable.

Offset-stoichiometric reflowable composite bonding method with adhesive for mitigating strict faying surface tolerances

Inherent susceptibility of adhesive bonds to miniscule quantities of contamination can cause undetectable weakened bonds. For this reason, the Federal Aviation Administration (FAA) places strict regulations on adhesively bonded joints in primary aircraft structures. To meet certification requirements aircraft manufactures resort to redundant load paths in the form of fasteners which inherently add weight to the structure and increase manufacturing time. In prior work, a secondary bonding technique called AERoBOND was developed, which utilized off-stoichiometric epoxy-matrix resins to facilitate reflow and diffusion of the resin within the joint interface during a secondary bonding/cure process, thus achieving a bond similar to a co-cured joint. However, the AERoBOND process required tight spatial tolerances between the two parts being joined. This study examined the utilization of conventional adhesive with the AERoBOND method to act as a filler in the joint line, effectively reducing the need for tight tolerances on the joining parts and serving as a flexible alternative for existing manufacturing processes. Ultrasonic inspection, optical microscopy, and ASTM International standard tests were performed to analyze the joints for defects and to quantify the mode-I and mode-II interlaminar fracture toughness and short beam strength of the proposed methodology with varying manufacturing parameters. The comprehensive results indicate that the AERoBOND+ method with and without surface preparation performs comparably to co-cured and conventional, adhesively bonded joints when secondary cured in an autoclave with 791 kPa of pressure. As an example, the AERoBOND+ panel without surface preparation bonded with 791 kPa of pressure (referred to as AB+3 throughout paper) had a mode-I fracture toughness (GIc) of 0.643 kJ/m2 and a mode-II fracture toughness (GIIc) of 4.000 kJ/m2 in the non-precracked condition and 4.218 kJ/m2 in the precracked condition at the adhesive-to-prepreg interface. These results were 96 %, 142 %, and 217 %, respectively, of a co-cured baseline panel (referred to as C1 throughout paper).

Characterization of Mechanical Properties and Surface Wettability of Epoxy Resin/Benzoxazine Composites in a Simulated Acid Rain Environment

Despite the robustness of thermosetting coatings in various applications, prolonged exposure to acidic environments can cause gradual deterioration, leading to structural or functional damage. This study investigates composite materials comprised of cycloaliphatic epoxy resin (CER) and benzoxazine (BZ) at three different weight ratios: 50:50, 25:75, and 0:100. These composites were exposed to nitric acid, simulating acid rain, for durations ranging from 1 to 5 h. The specimens were characterized for weight change, mechanical properties (flexural strength and short beam strength), and surface properties (contact angle and contact angle hysteresis). Although minimal changes in the physical and mechanical properties of both homopolymer and copolymer composites were detected after short acid exposure (up to 5 h), surface wettability analysis via static contact angle and contact angle hysteresis revealed more pronounced deterioration. The static contact angle decreased by 24.96% and 28.32% for homopolymer BZ and copolymer BZ-CER composites, respectively. Contact angle hysteresis increased by 19.39% and 27.80% for 5 h acid-exposed homopolymer BZ and copolymer CER, respectively. This study underscores the utility of surface wettability analysis as a valuable tool for monitoring deterioration from acidic aging in polymers, particularly in BZ-CER systems used in structural and high-performance applications.

The microstructural evolution of material extrusion based additive manufacturing of polyetheretherketone under different printing conditions and application in a spinal implant

AbstractWith the advances in additive manufacturing, polyetheretherketone (PEEK), a biocompatible polymer, can be used in biomedical applications such as spinal implants. This paper aims to investigate the evolution of the microstructure of PEEK parts manufactured by material extrusion (MEX)‐based additive manufacturing with different printing parameters. The effect of layer thickness (LT) and nozzle diameter on mechanical properties was investigated using tensile, Charpy impact, and short beam strength (SBS) tests. Two different LTs, 0.1 and 0.2 mm, and two different nozzle diameters, 0.6 and 0.8 mm, were used as printing parameters. By increasing the LT, tensile strength dropped by around 24%, and impact strength by almost 55%. Moreover, altering the LT resulted in a 15% decrease in interlaminar shear strength (ILSS) from the SBS test. In addition, increasing the nozzle diameter also led to a significant reduction in all of the results as tensile strength, Charpy impact strength, and ILSS. The results were also consolidated by scanning electron microscopy. The main findings were that increasing LT leads to an increase in microstructural defects that act as stress concentrators. Following the tests, response surface methodology (RSM) was used to determine optimal printing parameters. In the end, using the optimum printing parameters from the RSM study, a structural analysis of a MEX‐printed spinal implant was conducted through finite element method, considering the loading cases mimicking daily human body motions.Highlights As layer thickness increased, tensile and impact strength dropped. Tensile and impact strength dropped truly with increasing nozzle diameter. SEM revealed that increasing layer thickness causes more microstructural flaws. FEM analysis showed that PEEK‐based implant provides structural integrity.

Effect of Chemical Treatments on the Mechanical Properties of Jute/Polyester Composites.

Natural fiber composites have been extensively studied for structural applications, with recent exploration into their potential for various uses. This study investigates the impact of chemical treatments on the properties of Brazilian jute woven fabric/polyester resin composites. Sodium hydroxide, hydrogen peroxide, and peracetic acid were utilized to treat the jute fabrics, followed by resin transfer molding (RTM) to form the composites. Evaluation included water absorption, flexural strength, tensile strength, and short-beam strength. The alkaline treatment induced changes in the chemical composition of the fibers' surface. Chemical treatments resulted in increased flexural and short-beam strength of the composites, with no significant alterations in tensile properties. The hydrogen peroxide treatment exhibited lower water absorption, suggesting its potential as a viable option for enhancing the performance of these composites.

The distinctions of the interfacial nanostructures and properties between carbon fiber reinforced fast and conventional curing epoxy composites subjected to hydrothermal treatments

The vital role of the interphase in loading transfer in carbon fiber reinforced resin composites has received considerable critical attention. In this study, to quantitatively distinguish between the effects of hydrothermal aging on the interfacial nanostructures and properties of carbon fiber reinforced fast and conventional curing epoxy composites, peak force quantitative nano-mechanics (PF-QNM) technique by atomic force microscopy (AFM) was utilized to determine the interfacial modulus, adhesion and thickness. In addition, the shear behavior was studied by short-beam strength test, and the water uptake was investigated by water adsorption test. Based on the modulus contrast of the interphase in PF-QNM modulus image, the average interfacial thickness of the fast curing epoxy composites after 18 h of hydrothermal aging was 67 nm, increased 236 % when compared with the unaged composites. It was much higher than the rise of 70 % of the conventional curing epoxy composites after 18 h of hydrothermal aging while the interfacial thickness was 69 nm. Consistently, the average interfacial thickness of the fast and conventional curing epoxy composites determined by the adhesion were 68 nm (widened 247 %) and 68 nm (widened 67 %). In a word, the interfacial thickness of the fast curing epoxy composites was about 4 times than that of the conventional curing epoxy composites after 18 h of hydrothermal aging, because of the fast curing caused microcracks and flaws. Then, after 192 h of hydrothermal aging, the decreasing of short-beam strength of the fast curing epoxy composites were almost 1.6 times than that of the conventional curing epoxy composites, due to the faster growing of microcracks and delamination on the side surface of the fast curing epoxy composites short-beam samples during testing. Lastly, the maximum water absorption and diffusion coefficient of the fast curing epoxy composites were 1.2 % and 5.5 × 10−7 cm2/s respectively, which were both 1.3 times that of the conventional curing epoxy composites. Significantly, all the results proved that, attributing to the fast curing caused microcracks and flaws in the fast curing epoxy composites, through which water preferred to enter a composite along the fibers and interphase, the interphase in the fast curing epoxy composites were more sensitive to the hydrothermal aging than the conventional curing epoxy composites. Therefore, the water uptake, interfacial thickness and short-beam strength of the fast curing epoxy composites changed faster.

Strengthening and self‐healing of natural fiber composites via PLA core–shell nanofibers as healing agent carrier

AbstractThe resin‐rich region between the fiber laminates of a fiber‐reinforced composite is susceptible to matrix damage impeding the composite's integrity. Hence, this study intends to interlayer core–shell poly(lactic) acid (PLA) nanofibers between the flax fibers as a preventive and reactive mechanism to matrix damages in the resin‐rich area. The nanofibers prevent premature damage by suppressing or mitigating crack propagation and in the event of damage to the nanofibers, it reacts by releasing the encapsulated healing agent. Upon interlayering the flax fiber laminates with self‐healing core–shell nanofibers, the flexural modulus exhibited an increment of 31% whereas the short beam strength improved by 19%. Self‐healing traits of the composites were assessed by subjecting the composites to repeated flexural or short beam strength tests for several load cycles. Upon initial damage to the composites, the composites exhibited a full retention and improvement in mechanical properties. The self‐healing composites were also able to withstand more loading cycles than the conventional composite under repeated short‐beam strength tests. Under both configurations, the damaged self‐healing composites exhibited a residual strength greater than or equivalent to the ultimate strength of a pristine flax fiber composite.Highlights Fabrication of EP/flax self‐healing composites by PLA core–shell nanofibers. Interlayering healing nanofiber mats between flax fabrics in an FRP composite. Nanofiber interlayers exhibited a profound impact on the composite properties. Nano mats facilitate autonomous repair of internal defects within matrices. The self‐healing composites showed full retention and mechanical strength.

MECHANICAL PROPERTIES OF CNTS INTEGRATED PP/GLASS FIBER REINFORCED BIAXIAL WEFT-KNITTED THERMOPLASTIC COMPOSITES WITH DIFFERENT KNITTING STRUCTURES

In this study, four types of biaxial weft-knitted (BWK) fabrics (polypropylene (PP) resin yarn/glass fiber (GF) with different knitting structures such as plain (P), interlock (INT), tuck (T) and tuck&miss (TM) and multi-walled carbon nanotubes (MWCNTs) (0.4 wt%) were used as reinforcements to produce thermoplastic laminates with MWCNTs. In order to study the mechanical characteristics of the laminates, the flexural, short beam and Charpy impact tests on the samples were performed. In preliminary studies, the BWK fabrics with the plain knittings were used to produce the thermoplastic laminates with and without MWCNTs and positive effect of MWCNTs on the laminates were found out by performing the flexural tests on the specimens. The BWK laminates with the INT and TM knitting types with 0.4 wt% MWCNTs had almost same bending modulus and strength. 5% and 41% higher bending modulus and strength were gained with the BWK laminates with the interlock knitting type with 0.4-wt% MWCNTs compared to that was with the tuck type. 28.2% higher short beam strength and 57% higher Charpy impact energy were obtained with tuck&miss with 0.4-wt% MWCNTs (21.02 MPa and 6.34 Joule) compared to that was with the tuck knitting (16.39 MPa and 4.04 Joule).

The role of printing parameters on the short beam strength of 3D-printed continuous carbon fibre reinforced epoxy-PETG composites

It is well known that printing parameters strongly affect the mechanical performance of 3D printed parts. This work explores the role of i) extruder temperature, ii) print speed, and iii) layer height on the interlaminar strength of 3D-printed continuous fibre-reinforced composites. The carbon fibre-reinforced thermoset filament is printed concomitantly with polyethylene terephthalate glycol (PETG) thermoplastic filament in a single nozzle, characterising a continuous fibre co-extrusion (CFC) process. There is a significant variation in the short beam strength for composites printed with different parameters. The load–displacement curves have a similar pattern, with clear load peaks followed by a plastic zone. Optical micrographs and computed tomography (CT) scans reveal that the microstructure is dependent on the printing parameters. Image analysis elucidates the various mechanisms of void formation. Following the application of a three-way ANOVA and statistical tests to quantify the effects and interactions among variables, the analysis concludes that the extruder temperature has the highest influence, followed by print speed and layer height. When considering all possible interactions between the factors, the interaction between print speed and layer height is the most impactful.

Interfacial reinforcement of carbon fiber composites through a chlorinated aramid nanofiber interphase

Carbon fiber-reinforced polymers (CFRPs) rely on a strong interfacial bond between the reinforcing fibers and polymeric matrix to yield the high strength and toughness expected by a composite material. Poor interfacial strength leads to sub-optimal load transfer and introduces stress concentrations, which can reduce overall performance and result in catastrophic failure. Aramid nanofibers (ANFs) have shown significant promise for interfacial reinforcement in polymeric composite systems due to their high tensile strength, large specific surface area, and abundant polar functional groups. However, due to the chemically inert nature of carbon fibers, ANFs do not readily bond to their surface – thus limiting their application to CFRPs. In this work, we demonstrate that chlorination of ANFs and oxygen plasma treatment of carbon fibers enables the formation of a chlorinated ANF (Cl-ANF) interphase through chemical and physical adsorption using a simple dip-coating process, while fully preserving the tensile strength of the carbon fibers. The Cl-ANF interphase yielded a 79.8 % increase in interfacial shear strength and a 33.7 % increase in short beam strength. By enhancing the interfacial bond between fiber and matrix without degradation of the fiber's tensile strength, this method provides a rapid and reliable process to improve the mechanical properties of CFRP composites.

Effects of one-sided thermal shock and hold on alumina-based oxide/oxide ceramic matrix composites for temperatures in excess of 1200 °C

Nextel™720/alumina based ceramic matrix composite plates were subjected to one-sided thermal shock and 30-minute hold at 1100 °C, 1250 °C, 1400 °C and 1550 °C. Post exposure, the plates were evaluated for physical, structural, and microstructural changes using state-of-the art characterization techniques as well as standard mechanical testing procedures. Physically, no significant mass or dimensional changes were noted, while the surface roughness decreased on the exposed side for all the cases. Structurally, both the tensile and flexural strengths decreased for the 1550 °C case, but not for the other temperatures. In addition, short-beam strength tests showed no effect on interlaminar strength as a result of the elevated temperature exposures for the 30-minute duration considered. Microstructurally, SEM/EDS evaluations showed no significant change in the microstructure or element composition on the exposed and back sides. However, mercury intrusion porosity measurements did show a change in pore size distribution due to the combined effect of matrix shrinkage and further matrix microcracking. Combined results show that the operational limit of the composite can be pushed significantly beyond 1200 °C for shorter (in minutes) durations provided it is structurally viable for the application sought.

The use of recycled high‐density polyethylene waste to manufacture eco‐friendly plastic sand bricks

AbstractHigh‐density polyethylene (HDPE) polymer is one of the largest contributors to plastic wastes causing detrimental effects on various sectors of society, and is not biodegradable in nature. In the first stage, river sand and a recycled HDPE as a binder were used to manufacture eco‐friendly plastic sand bricks with various sand(s):plastic(p) ratios: 60s:40p; 65s:35p; 70s:30p; 75s:25p; 80s:20p; 85s:15p. In the second stage, 1%, 5%, and 10% of Kaolin Clay was added to each ratio of sand:plastic, respectively. Three mechanical tests were conducted: compressive strength, impact, and short beam strength. First, the addition of 5% Kaolin Clay to 75s:25p ratio increased compressive strength significantly from 21.4 to 52.76 MPa. Second, the addition of 10% Kaolin Clay in the ratio of 75s:25p mixture increased the impact strength from 4.8 to 5 J. Finally, the addition of 5% Kaolin Clay in the ratio of 60s:40p mixture increased the short beam strength significantly from 1.84 to 2.27 MPa. SEM analysis showed a well‐compacted interface indicating effective bonding between the HDPE and river sand particles in the 75s:25p ratio. Hence, the results of this study present a potential for the use of recycled HDPE plastic to manufacture plastic sand bricks.Highlights Addition of Kaolin Clay improved the mechanical properties of the composite material.

Superior high-temperature mechanical and thermal performance of carbon fiber/epoxy composites by incorporating highly dispersed aramid nanofibers

Enhancing the high-temperature properties of polymer-matrix fiber-reinforced composites is a challenging task, given the thermal limitations of polymer resins. In this study, we propose a straightforward and efficient method for producing high-performance carbon fiber/epoxy composites with superior high-temperature properties by incorporating highly dispersed aramid nanofibers. To achieve high dispersion of aramid nanofibers in the epoxy, we used a sequential solvent exchange method, which allowed us to fabricate B-stage cured resin films. The aramid nanofiber-hybridized carbon fiber composite, manufactured using resin film infiltration, demonstrated impressive mechanical and thermal properties. Specifically, in the glass transition temperature range at high temperatures, the composite provided 3.1, 5.1, and 6.8 times higher Young's modulus, tensile strength, and short beam strength, respectively, compared to the unmodified composite. Moreover, incorporating aramid nanofibers significantly increased the glass transition temperature by 31 °C, resulting in 2.4 times higher storage modulus and improved thermal stability with an increase in the total weight residue at 800 °C by 33.7 %. Therefore, the highly dispersed aramid nanofiber-embedded carbon fiber composite shows great potential for use in high-performance polymer composite applications.

Effects of thermal plasma on the microstructure and mechanical behavior of alumina-mullite based oxide/oxide ceramic matrix composites

Oxide/oxide ceramic matrix composites have potential applications in thermal protection systems due to their ability to withstand very high temperatures while maintaining their load bearing capability and oxidation resistance. Under hypersonic flight conditions vehicle components may be exposed to temperatures above the melting points of alumina and mullite, as well as to chemically active ionized gases. Therefore, it is necessary to understand the response of these CMCs to not just thermal loads, but also the added challenges of plasma environments. In this study, alumina-mullite based oxide/oxide CMCs were exposed to an inductively generated plasma jet for 30 min at a heat flux of 24 W/cm2 in near vacuum conditions. Resulting microstructures were characterized with XRD and SEM/EDS. Silicon rich, sub-micron globules were observed on the surface of the impinged region. Also, the first 5 μm below the surface were enriched with silicon. The back surface showed no silicon enrichment but did have a granulated surface texture in comparison to as manufactured samples. Short beam strength tests were performed as a measure of structural performance. Differences in the overall response and short beam strength were noted between the as manufactured and plasma exposed cases.

Hybrid wood-glass and wood-jute-glass laminates manufactured by vacuum infusion

Hybrid unidirectional wood-jute laminates manufactured by the vacuum infusion processing (VIP) may present some limitations, including high incidence of delamination failures, low interfacial adhesive strength and low transverse mechanical strength. This study proposes a way to overcome these issues by manufacturing wood-glass and wood-jute-glass laminates by VIP. Pine wood veneers, jute nonwoven fabrics, glass mats and a polyester resin were employed in the here studied five-layer laminates. Apparent density, compressive, longitudinal flexural, transverse flexural, short beam testing, morphology and water absorption were the characterization analyses. As expected, the higher the number of glass layers, the higher the apparent density (up to 30%), the thinner the laminates, the closer the longitudinal and transverse mechanical properties and the smaller the water uptake levels. Based on increases of up to 70% in short beam strength, the wood-glass interface bonding was more qualified than the wood-jute one. Among all laminates, those ones with glass mats as faces showed higher longitudinal and transverse flexural properties. Besides, the higher the number of jute layers, the higher the void content.

Manufacture of antibacterial carbon fiber-reinforced plastics (CFRP) using imine-based epoxy vitrimer for medical application

An antibacterial carbon fiber-reinforced plastics (CFRP) was manufactured based on a vitrimer containing imine groups. A liquid curing agent was prepared to include an imine group in the matrix, and was synthesized without a simple mixing reaction and any purification process. The vitrimer used as the matrix for CFRP was prepared by reacting a commercial epoxy with a synthesized curing agent. The structural and thermal properties of the vitrimer were determined by Fourier transform-infrared spectroscopy (FT-IR), differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA). In addition, the temperature-dependent behavior of the vitrimer was characterized by stress relaxation, reshaping, and shape memory experiments. The mechanical properties of composites fabricated using vitrimer were fully analyzed by tensile, flexural, short-beam strength, and Izod impact tests and had mechanical properties similar to reference material. Moreover, both the vitrimer and the vitrimer composites showed excellent antibacterial activity against Staphylococcus aureus and Escherichia coil due to the imine group inside the vitrimer. Therefore, vitrimer composites have potential for applications requiring antimicrobial properties, such as medical devices.

Enhancing the interfacial bonding strength between 3D-printed aluminium substrates and carbon fibre–reinforced polymers

Carbon fibre–reinforced polymers (CFRP) are increasingly utilised as materials within hybrid components in combination with plastics and metals. Although hybrid components provide a combination of advantages from the constituent materials, there are some challenges for the manufacture of high-quality hybrid components, including weak interface bonding between the constituent materials. This research focuses on utilising additive manufacturing (AM) technology to control an aluminium substrate's surface features to enhance interfacial bonding with a CFRP laminate. For this purpose, different surface structures were designed and manufactured using laser powder bed fusion (LPBF) technology to understand the influence of surface geometry and roughness on the interface. A lattice structure with a unit cell size of 3 × 3 × 1.5 mm was manufactured to create a substrate surface with porosity. A second substrate surface was designed with the same lattice structure; however, the voids were filled to present an equivalent surface topology (EST), excluding porosity. This comparison provides an understanding of the influence of the porosity of the substrate surface on interfacial bonding strength. Interfacial bonding between the aluminium substrates and a CFRP laminate was assessed using short beam strength (SBS) and flatwise tensile tests. The results from the SBS testing indicated a 3D-printed substrate with random surface roughness increased the interlaminar shear strength of the hybrid component by almost 200% compared to a hybrid laminate with non-printed substrate. The results from flatwise tensile tests illustrated that the out-of-plane bonding strength can also be improved significantly (almost 100%).

Fire impact on mechanically failed graphite/epoxy composites

AbstractAircraft crashes often initiate or accompany fire incidents. Post‐crash fires, in particular, can mask or destroy critical fractographic failure features necessary for accident reconstruction. As a first step in developing a coherent strategy for composite aircraft post‐crash forensic analysis, a series of vertical flame tests were performed on mechanically failed Cytec T40‐800/Cycom® 5215 graphite/epoxy unnotched compression, short beam strength, and in‐plane shear specimens. Visual inspection and scanning electron microscopy were used to examine the specimens fracture surfaces before and after fire testing. The fire‐induced damage included matrix decomposition, melt dripping, char, soot, delamination, and residual thickness increases. The composite thermal degradation was significantly influenced by the specimen stacking sequence, the fracture surface morphology, and the total available free surface area. In addition, microscopic inspection showed that char layers impeded heat conduction and oxygen transfer to the interior of the specimens resulting in less thermal damage to the underlying plies. Moreover, burned specimens with more available free surface area sustained more thermal degradation and fire combustion damage for a given fire exposure duration. Exposed fiber bundles from the fracture surfaces were susceptible to severe thinning and thermal oxidation, which destroyed critical fractographic failure features necessary for accident reconstruction.

High-performance wood scrimber prepared by a roller-pressing impregnation method

Wood scrimber is a wood-based composite material with high mechanical strength and large size, which can potentially replace the use of steel and cement in various fields. However, its poor dimensional stability and low flame retardancy limit its use in outdoor construction projects and fire-prone areas. To solve this, here we report a roller-pressing impregnation method to realize the deep penetration of resin using mechanical compression and low-pressure adsorption. Microstructural imaging by SEM and 3D ultra-deep field microscopy shows the phenol formaldehyde(PF) resin distribution of the roller-pressed wood scrimber (R-WS) is deeper and more uniform, which increases the flatness and crystallinity. The R-WS showed greatly improved dimensional stability, with 63 % and 35 % lower thickness swelling rate (TSR) and width swelling rate (WSR) compared with the traditional wood scrimber (T-WS). In terms of flame retardancy, the smoke production rate (SPR) and heat release rate (HRR) of R-WS decreased by 32.7 % and 52 %, respectively. The R-WS at 800 °C formed a dense char that content increased by 20 %, helping to inhibits combustion. The mechanical properties of R-WS were also improved, and the modulus of rupture (MOR), modulus of elasticity (MOE) and short-beam strength (SS) of R-WS increased by 31.2 %, 7.4 %and 26.7 %, respectively. The R-WS suffer toughness failure and wood-to-wood failure under bending and shear scenarios, respectively, indicating that the roller-pressing impregnation treatment enhanced toughness and bonding strength. In addition, the use of a rotating roller is expected to realize the continuous production of the dipping link, saving drying energy consumption and improving production efficiency. These properties are expected to promote the outdoor utilization and continuous production of wood scrimber.

Development of Lightweight Cricket Pads Using Knitted Flexible Thermoplastic Composites with Improved Impact Protection.

Cricket is one of the most popular global sports, and cricket pads are important personal protective gear used for shock absorption and peak deceleration of the impact forces of the cricket ball for both batsmen and wicket keepers. The materials selection of the padding should be considered according to requirements. In the present study, flexible composites were manufactured using knitted unidirectional thermoplastic composite prepregs. Prepregs were fabricated using thermoplastic yarns, e.g., High Density Polyethylene (HDPE), Polypropylene (PP), and Low Melting Polyester (LMPE). Para-aramid (Kevlar) and Flax yarns were used as inlay. The structures were stacked in three and five layers, and hot compression was used to convert thermoplastic yarn into matrix. A total of twelve samples were prepared, and their mechanical properties were evaluated. Tensile and flexural properties, short beam strength, and impact properties were optimized using the multi-criteria decision-making (MCDM) technique for order performance by similarity to ideal solution (TOPSIS). This approach was used to select the best material for use in cricket pads. The candidate samples were ranked using statistical techniques. The optimum sample was found to be FP5, i.e., Flax with polypropylene using five layers, which exhibited the maximum impact strength. The results showed that the mechanical properties were improved in general by increasing the number of layers. The significance and percentage contribution of each factor was obtained by ANOVA (α = 0.10) and pie chart, which showed Factors A and C (inlay yarn and number of layers) to be the main contributors. The optimal samples showed superior impact-related performance compared to a market sample cricket pad.