Journal of Reinforced Plastics and Composites

This research addresses the problem of accurately quantifying the strain rate effect of carbon fibre-reinforced plastics by proposing a method with a simple specimen manufacturing and experiment execution based on four-point bending tests. By easing the strain rate-dependent characterization of carbon fibre-reinforced plastics, less conservative designs can be achieved. The method proposed uses Euler–Bernoulli and Timoshenko’s beam theories to obtain the longitudinal compressive and tensile modulus, compressive strength, shear modulus, and shear yielding point. Transverse properties could not be obtained due to limitations of the fixture employed. A strain-dependent material characterization was done using the proposed method and compared to the characterization of the same material using traditional uniaxial tests. Most of the material properties obtained with different methods correlated within approximately 10%. More work needs to be done to determine how this discrepancy affects simulation results.

This work presents a numerical modelling study on the bending response and failure mechanisms of aramid skin/aluminium honeycomb core sandwich panels under quasi-static bending loads. These composite sandwich panels are widely used in aerospace and automotive industries, in spite of the limitations for their use in complex structures, such as the extensive experimental testing needed at the component and full-size structural levels, which are expensive and time-consuming. The aim of this study was to capture the initiation of different failure mechanisms and their multiple interactions, which are known to strongly influence the observed microscopic behaviour of the material. Furthermore, a series of detailed Finite Element models were built and analysed in an attempt to replicate the complex damage mechanisms observed experimentally. The results show good correlation between numerical models and experimental results, both in terms of the global load–displacement behaviour and the observed damage mechanisms, including skin in-plane shear and compression damage, intralaminar fracture, delamination within the skin and core crushing. No debonding between the core and the skins was evidenced. It is proposed that this modelling approach can become a feasible alternative to component-level experimental testing when designing complex sandwich structures.

This paper presents an analytical method to solve the dynamic crushing force and collapse characteristics of rotational ellipsoidal composite-reinforced metal shells with foam filler. The collapse model is firstly simulated by means of finite element calculation. Then, the feasibility of the analytical method is proved by a comparison with the finite element simulate. In example calculations, effects of some key parameters on the dynamic crushing force of rotational ellipsoidal composite-reinforced metal shells with foam filler are described and discussed. Results obtained can be used as a valuable reference for the design of protective structures resisting impact loads.

A lattice sandwich structure mainly consisting of jute fiber and resin epoxy was prepared. Two configurations were established, and six out-of-plane compression experiments were conducted to identify the factors affecting the mechanical properties of the samples. The specific strength of the 2D corrugated lattice truss with the struts at 30° (I₁) was 3 times stronger than that of the sample with sandwich struts at 45°. The specific strength of I₁ was 3.9 times stronger than that of the Kagome structure prepared using Cu–2%Be. The cost performance with respect to the specific strength of the structure I₁ was 161.7 times higher than that of the Kagome structure prepared using Cu–2%Be. Three failure modes were considered, and theoretical predictions were made separately. The failure modes in the experiment were mainly shear failure and shear buckling failure in sandwich struts.

In this work, the residual strength of a fiber-reinforced injection molded part containing a hot weld line—or meld line—was evaluated. Injected plates were generated using a double-gated mold under four different process conditions. Quantification of the weld line detrimental effect was made in base on a fracture mechanics experiment. Specimens with and without the weld line—obtained from the same plates—were tested under a clamped single edge notched tension (SENT) configuration. For each set of process conditions, a relative weld line strength factor was defined in terms of the maximum applied stress intensity factor (K_Imax) as: K_Imax of specimens with weld line/K_Imax of specimens without weld line. In parallel, the fiber distribution pattern was obtained by process simulation software Moldex3D. An orientation factor was determined from simulation in order to quantify the effect of the local fiber orientation around the weld line. Optimal process condition and the most significant variable influencing the weld line strength were calculated via statistical analysis. Results showed a clear correlation between the weld line strenght factors and the orientaion factor. It was demonstrated that the fracture performance of the weld line region is controlled by the fiber orientation arrangement developed on that zone.

The application of natural fibers as reinforcement material in composites can make an important contribution toward a more sustainable bio-based economy. To use these natural fibers, they need to be released from the stem. Traditionally, this is realized by dew retting. However, there are some disadvantages to this retting procedure. Due to changing weather conditions, it is quite difficult to guarantee a good and consistent fiber quality. Replacing the traditional retting process by a biocatalytic process may resolve these issues through application of a combination of pectinase and hemicellulase activities. In this context, several strategic pectinase and hemicellulase activities were blended. Flax fiber fineness and mechanical properties of resulting unidirectional fiber–epoxy composites were studied after treatment of flax stems with these strategic enzyme combinations. Characterization of fiber fineness showed a higher percentage of fiber widths smaller than 100 µm after combined treatment with two enzymes (44.7%), and the percentage was even higher after some combinations with three enzymes (51.2%). Assessment of mechanical properties of composites showed no significant differences in tensile or transverse properties for combined enzymatic treatments. Fiber properties were back-calculated from unidirectional flax fiber–epoxy composites and a Young’s modulus of 88 GPa and a tensile strength of 865 MPa were observed. Enzymatic extraction resulted in the achievement of similar results as dew retting concerning mechanical composite performance and fiber fineness.