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This study assesses the out-of-plane bending performance of cross-laminated timber (CLT) panels made from Japanese cedar to determine the bending modulus of elasticity ( E ) and shear modulus ( G ) through both dynamic and static testing methods. Six CLT layups, as defined by the Japanese Agricultural Standard (JAS) 3079, were tested in both major and minor strength directions. The findings reveal that E values obtained from the Timoshenko–Goens–Hearmon (TGH) method, the variable span method, and the shear-free (local) values of the out-of-plane bending test were generally consistent. However, the values derived from the transformed section method were generally lower, especially in the minor strength direction. The TGH method consistently yielded higher G values compared to the variable span method, which exhibited irregular patterns in minor strength direction layups with fewer layers. The E / G ratios from the variable span method reached approximately 80 for certain layups in the major strength direction, surpassing the default value of 50 used in JAS 3079. This indicates the need for an adjustment factor near 0.85, rather than the default 0.9 specified in JAS 3079. While the 0.9 adjustment factor is appropriate for most CLT layups, it can underestimate deformation in those susceptible to rolling shear. In addition, out-of-plane bending test results show that the 0.65 reduction factor from the Notification of the Ministry of Land, Infrastructure, Transport and Tourism is suitable for the major strength direction but may be too conservative for layups in the minor strength direction.

Fiber-reinforced composites are gradually replacing the traditional materials in many engineering applications. However, for many applications these materials are still unsuitable, due to their lack of toughness. In this context, hybridization is a promising strategy in which two or more types of fiber are combined to obtain a better balance of mechanical properties compared to non-hybrid composites. Therefore, the main goal of this work is to study the hybridization effect on the static performance and interlaminar shear strength. For this purpose, carbon, glass, and Kevlar fibers were used and combined in different proportions. It was possible to conclude that there is an ideal value of fiber content to maximize both properties and, depending on the type of fiber, they should be placed specifically on the compression or tensile side. For example, for composites involving carbon and glass fibers the latter must be placed on the compression side, and for a value of 17% by weight the flexural strength decreases by only 2.8% and the bending modulus by around 19.8%. On the other hand, when Kevlar fibers are combined with glass or carbon fibers, the Kevlar ones must always be placed on the tensile side and with an ideal value of 13% by weight.

The influence of the moisture and heat environment on the bending properties of CFRP laminates and CFRP reinforced foam sandwich structures was studied by mass change and three-point bending test. The results show that the saturation moisture absorption rate of CFRP laminates is low, only 0.62%. The CFRP reinforced foam sandwich structure exhibits a saturation moisture absorption rate of 1.48%. Humidity and heat have little effect on the bending modulus of CFRP laminates but have some effect on the bending strength, which decreases by 13.23% compared with normal temperature and dry conditions. The flexural strength and average energy absorption of CFRP reinforced foam sandwich structure decreased by 11.5% and 5.56% under hot and humid environments. The flexural fracture of the CFRP foam sandwich structure is smooth under normal temperatures and dry conditions. Many fibers are pulled out, and the resin falls off, obviously under hot and humid environments. The stratification of CFRP panels and foam cores in hot and humid environments is more obvious than in dry conditions at normal temperatures.

Bamboo particles as reinforcement in composite materials are prospective to be applied to particleboard products in the industry. This study aimed to synthesize bamboo particle reinforced polymer composites as a substitute for particleboard products, which still use wood as a raw material. The parameters of the composite synthesis process were varied with powder sizes of 50, 100, and 250 mesh, each mesh with volume fractions of 10, 20, and 30%, matrix types of polyester and polypropylene, Tali Bamboo, and Haur Hejo Bamboo as reinforcements. Characterization included tensile strength, flexural strength, and morphology. Particleboard products were tested based on JIS A 5908-2003, including density testing, moisture content, thickness expansion after immersion in water, flexural strength in dry and wet conditions, bending Young’s modulus, and wood screw holding power. The results showed that the maximum flexural and tensile strength values of 91.03 MPa and 30.85 MPa, respectively, were found in polymer composites reinforced with Tali bamboo with the particle size of 250 mesh and volume fraction 30%. Particleboard made of polypropylene and polyester reinforced Tali Bamboo with a particle size of 250 mesh and a volume fraction of 30% composites meets the JIS A 5908-2003 standard.

This article discusses the non-destructive evaluation of the mechanical properties of green wood. To estimate the dynamic flexural modulus of elasticity (MOED), a non-destructive test (NDT) method—the frequency resonance technique (FRT)—was used. A three-point bending test was carried out to determine the static bending properties as the bending modulus of elasticity (MOE), the modulus of rupture (MOR), and bending toughness (Aw). This article presents the results of a study comparing the correlations between the dynamic and static bending parameters of beech (Fagus sylvatica L.) and oak (Quercus robur L.) wood, which was further divided into heartwood and sapwood. These species were chosen as the most widespread representatives of diffuse-porous and ring-porous hardwoods. This study found statistically significant differences in most mechanical parameters between the two species, except for MOR. Among the investigated parameters, beech had higher values than oak (by 22.1% for MOED, 9.5% for MOE, and 12.1% for Aw). Furthermore, relevant correlations (R > |0.7|) were established between MOED and between some of the static flexural parameters. These correlations were stronger for beech, which due to its more homogeneous structure showed less data variability than the ring-porous oak.

In order to improve the mechanical and bond properties of epoxy adhesives for their wide scope of applications, modified epoxy adhesives were produced in this study with SiO2 nanoparticles of 20 nm in size, including inactive groups, NH2 active groups, and C4H8 active groups. The mechanical properties of specimens were examined, and an investigation was conducted into the effects of epoxy adhesive modified by three kinds of SiO2 nanoparticles on the bond properties of carbon fiber reinforced polymer and steel (CFRP/steel) double lap joints. According to scanning electron microscopy (SEM), the distribution effect in epoxy adhesive of SiO2 nanoparticles modified by active groups was better than that of inactive groups. When the mass fraction of SiO2-C4H8 nanoparticles was 0.05%, the tensile strength, tensile modulus, elongation at break, bending strength, flexural modulus, and impact strength of the epoxy adhesives reached their maximum, which were 47.63%, 44.81%, 57.31%, 62.17%, 33.72%, 78.89%, and 68.86% higher than that of the EP, respectively, and 8.45%, 9.52%, 9.24%, 20.22%, 17.76%, 20.18%, and 12.65% higher than that of the inactive groups of SiO2 nanoparticles, respectively. The SiO2 nanoparticles modified with NH2 or C4H8 active groups were effective in improving the ultimate load-bearing capacity and bond properties of epoxy adhesives glued to CFRP/steel double lap joints, thus increasing the strain and interface shear stress peak value of the CFRP surface.

An unsaturated ladder phenyl/vinyl polysilsesquioxane (PhVPOSS) was synthesized and applied to vinyl ester resin (VER) thermosets. The compatibility, mechanical properties, thermal properties, and combustion behavior of the VER-PhVPOSS composites were further investigated. As a result, the PhVPOSS and VER had a good compatibility and interaction based on the solubility parameters and Flory–Huggins parameters. PhVPOSS provided the VER with a significantly enhanced bending strength, thermal stability, and smoke-suppression effect. When 20 wt% PhVPOSS was added, the bending strength, flexural modulus, and breaking force increased by195.6%, 260.6%, and 196.6% compared with pure VER. The peak heat release rate, total smoke release, and specific optical density decreased by 52.2%, 20.7%, and 15.7%, respectively. These favorable characteristics indicated that PhVPOSS had a good application prospect in unsaturated polyester resin. Graphic abstract

Climbing monocots can develop into large bodied plants despite being confined by primary growth. In our study on Flagellaria indica we measured surprisingly high stem biomechanical properties (in bending and torsion) and we show that the lack of secondary growth is overcome by a combination of tissue maturation processes and attachment mode. This leads to higher densities of mechanically relevant tissues in the periphery of the stem and to the transition from self-supporting to climbing growth. The development of specialised attachment structures has probably underpinned the evolution of numerous other large bodied climbing monocot taxa. Plants with a climbing growth habit possess unique biomechanical properties arising from adaptations to changing loading conditions connected with close attachment to mechanical supports. In monocot climbers, mechanical adaptation is restricted by the absence of a bifacial vascular cambium. Flagellaria indica was used to investigate the mechanical properties and adaptations of a monocot climber that, uniquely, attaches to the surrounding vegetation via leaf tendrils. Biomechanical methods such as three-point bending and torsion tests were used together with anatomical studies on tissue development, modification and distribution. In general, the torsional modulus was lower than the bending modulus; hence, torsional stiffness was less than flexural stiffness. Basal parts of mature stems showed the greatest stiffness while that of more apical stem segments levelled off. Mechanical properties were modulated via tissue maturation processes mainly affecting the peripheral region of the stem. Peripheral vascular bundles showed a reduction in the amount of conducting tissue while the proportion and density of the bundle sheath increased. Furthermore, adjacent bundle sheaths merged resulting in a dense ring of fibrous tissue. Although F. indica lacks secondary cambial growth, the climbing habit is facilitated by a complex interaction of tissue maturation and attachment.

This research contributes to the study of prickle sensation in terms of single fiber bending modulus and flexural rigidity, which are important factors for fabric-evoked prickle for garment tactile comfort. In this study, a novel technique was used to study the flexural buckling behavior of single fibers using an axial fiber-compression-bending analyzer (FICBA). The bending behavior and bending equivalent modulus of different single fibers were measured and analyzed. The bending properties of single fibers were quantified by calculating the equivalent bending modulus, and the flexural rigidity via measurement of the protruding length (l), diameter (d) of single fiber, and its critical force (Pcr), obtained from the peak point of the force–displacement curve. The experimental results indicate that ramie single fiber has the highest bending modulus, while cotton has the lowest bending modulus. However, hemp, jute, wool, flax, and cashmere fiber have bending modulus values lower than ramie but higher than cotton. On the other hand, the flexural rigidity of jute fiber is higher than that of wool followed by ramie, hemp, flax, cashmere, and cotton consecutively. Therefore, jute, wool, and ramie are stiffer than the other fibers, especially jute fiber. Thus, jute, wool, and ramie are uncomfortable single fibers because the fabric-evoked prickle, which is caused by short, coarse, and stiff fibers protruding from the fabric surface, generate sufficient force to evoke a low level of activity on a human nociceptors, but insufficient to penetrate the human skin so as to cause itchiness.

This study prepares composite panels with three Polylactic acid (PLA)-based materials via the multi-material fused filament fabrication method. The influences of four processing parameters on the mechanical properties of 3D-printed samples are investigated employing the Taguchi method. These parameters include the relative volume ratio, material printing order, filling pattern, and filling density. A “larger is better” signal-to-noise analysis is performed to identify the optimal combination of printing parameters that yield maximum bending strength and bending modulus of elasticity. The results reveal that the optimal combination of printing parameters that maximizes the bending strength involves a volume ratio of 1:1:2, a material sequence of PLA/foam-agent-modified eco-friendly PLA (ePLA-LW)/glass fiber-reinforced eco-friendly PLA (ePLA-GF), a Gyroid filling pattern, and a filling density of 80%, and the optimal combination of printing parameters for maximum bending modulus involves a volume ratio of 1:2:1 with a material sequence of PLA/ePLA-LW/ePLA-GF, a Grid filling pattern, and 80% filling density. The Taguchi prediction method is utilized to determine an optimal combination of processing parameters for achieving optimal flexural performances, and predicted outcomes are validated through related experiments. The experimental values of strength and modulus are 43.91 MPa and 1.23 GPa, respectively, both very close to the predicted values of 46.87 MPa and 1.2 GPa for strength and modulus. The Taguchi experiments indicate that the material sequence is the most crucial factor influencing the flexural strength of the composite panels. The experiment result demonstrates that the flexural strength and modulus of the first material sequence are 67.72 MPa and 1.53 GPa, while the flexural strength and modulus of the third material sequence are reduced to 27.09 MPa and 0.72 GPa, respectively, only 42% and 47% of the first material sequence. The above findings provide an important reference for improving the performance of multi-material 3D-printed products.