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This study investigates the use of hemp/glass fiber reinforced epoxy composites for designing automotive front bumper beams, focusing on crashworthiness and pedestrian safety. The composite bumper beam model is evaluated through low- and high-velocity crash simulations and pedestrian leg form impact tests using LS-DYNA software. Optimal stacking sequences are analyzed, with high-strength glass fibers positioned on the outer layers to bear impact loads and low-density hemp fibers in the middle. The hybrid hemp (H)/glass (G) fiber composite laminate can absorb up to 90 % of the impact energy absorbed by a glass fiber composite, with a ± 45° fiber orientation, showing exceptional energy absorption capabilities. The [G(±45°) 4 , H(±45°) 4 ] S composite bumper beam offers superior impact performance, safety, and a weight reduction of 49.2 % compared to a commercial steel bumper beam. This study highlights the potential of natural fiber composites as sustainable alternatives in automotive design. [ABSTRACT FROM AUTHOR]

• Mode I fracture process is characterized for GFRP-steel bi-material interface. • Double-cantilever beam experiments supplemented by detailed DIC measurement. • Accurate modeling of crack initiation, fiber bridging and propagation by new CZM. • Four-linear traction-separation law derived from DIC measurements and iterative FEA. Debonding is characterized as the governing failure mode in the innovative wrapped composite joints made with glass fiber composite material wrapped around steel hollow sections without welding. The prerequisite for predicting debonding failure of wrapped composite joints is to obtain fracture behavior of the composite-steel bonded interface. The mode I fracture behavior of the bonded interface was experimentally investigated using glass fiber composite-steel double cantilever beam (DCB) specimens. The crack length a and the crack tip opening displacement (CTOD) during the test were accurately measured by analyzing the digital image correlation (DIC) data while the strain energy release rate (SERR) was calculated through the extended global method (EGM). The cohesive zone modeling (CZM) was utilized in the finite element model with the proposal of a four-linear traction-separation law to simulate the mode I fracture process. An approach is introduced to determine the critical stages of the proposed four-linear cohesive law by combining accurate measurements of crack length a and CTOD, along with SERR values. The validity of the four-linear cohesive law and the introduced approach to determine the critical stages were confirmed by good agreement in both global and local behavior between the testing and the FEA results. [ABSTRACT FROM AUTHOR]

Hybrid carbon/glass fibers composites can possess pseudo-ductility of progressive failure through material design to achieve the function of load early warning. The printing design and forming thermal environment of parts have important influence on the pseudo-ductile behavior of hybrid fiber composites. In this paper, the hybrid continuous carbon/glass fibers reinforced nylon composites with progressive failure pseudo-ductility were prepared by additive manufacturing, and the effects of printing layer thickness, carbon/glass fibers layer ratio and forming thermal environment on the tensile properties and pseudo-ductility of hybrid fiber composites were investigated and characterized. The results indicate that the printing layer thickness has no significant impact on the tensile strength of hybrid fiber composites, the pseudo-ductility is obvious when the layer thickness of [G 5 C 2 G 5 ] is 0.075 mm and 0.125 mm. With the same material ratio, reducing the layers or setting the printing platform temperature (100 °C) can decrease defects generation to achieve the better pseudo-ductility. However, the pseudo-ductility immensely weakens using the annealing treatment of 120 °C for 3 h. The pseudo-ductility of the [G 5 C 2 G 5 ] 0.075 , [G 5 C 2 G 5 ] , [G 3 C 1 G 3 ] and [G 4 C 1 G 4 ] samples have been discovered successfully. [ABSTRACT FROM AUTHOR]

Abstract This paper studies the feasibility of improving structural performance of composites in the presence of stress concentrators. Matrix grading through local deposition of additive-enhanced matrices and fibre steering by varying fibrous architecture are examined independently and in combination on a glass-fibre triaxial braided composite subjected to open hole tensile test. Stiffened and toughened matrices were incorporated through precise point-wise injections of liquid reactive resin into dry preforms (Liquid Resin Printing). Fibre steering was implemented by varying the braiding angle along the length of the braided sleeve. It has been shown that these novel forms of architecture modification enable a significant improvement in composite strength through a variety of deformation mechanisms. This includes local stiffening of composite in the direct vicinity of the stress concentrator and damage accumulation away from the stress concentrators. The experimental observations are explained by using simple finite-element models. [ABSTRACT FROM AUTHOR]

• Hybrid continuous carbon/glass fiber composites based on different laminated design have been 3D printed. • The prepared hybrid fiber composites have excellent balance of impact resistance and tensile resistance. • The tensile strength prediction model considering hybrid effect with good applicability is established and verified. Material extrusion has been applied to the preparation of continuous fiber reinforced resin composites successfully. However, due to the limitations of the characteristics of a single fiber material, the prepared composites usually can only obtain the reinforcement of a single properties. In this study, the effects of the content ratio and arrangement mode of carbon/glass fiber layers in the 3D printed composites on tensile and impact properties were investigated, and the influence of mixed fibers was analyzed by failure morphology. The hybrid continuous carbon/glass fiber reinforced nylon composite parts with good balanced tensile and impact properties were obtained in the experiment, compared with single carbon fiber reinforced nylon composites, the impact strength increased to 250% of the original, while the tensile strength lost only 7%. Tensile strength and impact strength of the printed hybrid composites with the same fiber content and different arrangement are different by 20% and 35%, respectively. The tensile strength of 3D printed hybrid continuous fiber composites was accurately predicted by establishing a model considering hybrid effect. [ABSTRACT FROM AUTHOR]

This study presents experimental investigation and formulation of a new anisotropic nonlinear thermo-viscoelastic constitutive model to understand the time-dependent multi-axial responses of polyamide composites subjected to various histories of mechanical loading at several isothermal temperatures: 20 °C-100 °C. The composites were tested under uniaxial tension along 0° and 90° injection molding directions and the axial and lateral responses of the specimens were recorded. Experimental results indicate that composites exhibit pronounced time-dependent responses, even at low temperatures, and mechanical loadings, even at relatively low strain levels, cause permanent deformations and hysteretic responses. A new constitutive model that accounts for continuous microstructural changes under thermo-mechanical stimuli was formulated to describe the macroscopic anisotropic responses of the composites. The model was derived based on a multi-network approach and the microstructural changes are governed by the deformations of the composites. Elevated temperatures soften the polymers, making it easier to deform the composites, and thus accelerate the microstructural changes. The model is shown capable of describing mechanical responses of polyamide composites under various loading conditions, loading histories, and temperatures. [ABSTRACT FROM AUTHOR]

This paper presents an experimental and modelling study that determined the influence of thickness on the softening-rate, composite damage initiation and propagation, and structural survivability of composite structures in fire. Fire-under-compression load tests were conducted using glass fibre reinforced vinyl-ester laminates of varying thicknesses to quantify the influence of thickness on fire structural survivability. The matrix softening and degradation rates decreased as the composite thickness increased. The laminate thickness variations had a strong influence on the fire-under-compression load performance and failure mode. The analysis reveals complex multi-mode failure mechanisms involving global buckling and transitioning into shear dominated failure as the composite thickness increased. A thermal–mechanical model that can predict the time-to-failure of glass fibre reinforced composite subjected to a combined compression and fire load was developed and its validity was assessed by comparing the theoretical predictions to the experimental data. [ABSTRACT FROM AUTHOR]

• Hygrothermal environment has a significant effect on the strength of glass fiber composites. • Hygrothermal environment has little effect on the tensile stiffness of glass fiber composites. • Hygrothermal environment shortens the damage process of glass fiber composites under tension. • Hygrothermal environment changes the failure diagram of glass fiber composites under tension. In this paper, a progressive damage model considering hygrothermal effect is established. Taking high strength glass fiber composite plate as an example, the progressive damage model of open-hole composite plate is established, and the ultimate tensile and compressive strength at room temperature, dry state and hygrothermal environment are predicted. The model was verified by comparing with the experimental results. The results of numerical simulation and experiment show that the hygrothermal environment has a significant effect on the ultimate strength of open-hole composite plate. The tensile ultimate strength of open-hole composite plate decreases about 39% and the compressive ultimate strength decreases about 35% at 70 °C and equilibrium moisture absorption. The results show that hygrothermal environment has little effect on the tensile stiffness of open-hole composite plate, and the tensile modulus decreases by 6% at 70 °C and equilibrium moisture absorption. According to the numerical results, the hygrothermal environment can shorten the damage propagation process of the open-hole composite plate under tensile load, but does not affect the damage propagation process under compression load. The hygrothermal environment can change the macro failure diagram of the open-hole composite plate under tension from "X" to "I", but does not affect the macro failure diagram of the open-hole composite plate under compression. [ABSTRACT FROM AUTHOR]

Glass fiber-reinforced composites have been used as a secondary barrier structure in LNG cargo containment systems (CCS) for their excellent strength and corrosion resistance. However, during LNG transport, the tanks experience periodic thermal and bending stress because of the cryogenic environment. These conditions degrade the mechanical properties of the composites in the CCS. In this study, finite element analysis was conducted using the mechanical properties of each composite. A quasi-static tensile test was carried out, and the coefficients of thermal expansion were used to obtain the mechanical properties. To verify the reliability of the numerical analysis, modeled structural unit specimens were manufactured, and 3-axis strain gauges were attached to measure thermal strain under cryogenic conditions. Validation of the strain between experiments and computation was performed, and the finite element analysis was conducted based on the observed mechanical properties and their reliability. [ABSTRACT FROM AUTHOR]