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• The strain rate effects on the compressive strengths of a T-2.5DWC are clarified. • A mesoscopic finite element model accounting for the strain rate effects is developed. • The progressive damage behaviors of a T-2.5DWC under dynamic compressive loads are revealed. Understanding the mechanical failure behavior of 2.5D woven composites (2.5DWC) is challenging due to their complex fabric configurations and multi-scale structural properties. This challenge is particularly prominent in the realm of dynamic mechanical properties and damage failure mechanisms under high strain rates. Therefore, a comprehensive approach combining a series of quasi-static and dynamic mechanical tests with mesoscale finite element simulation methods is adopted to perform an in-depth analysis of the mechanical response and progressive damage behaviors of a Twilled 2.5D Woven Composite (T-2.5DWC) under different strain rate loads. The results indicate that the compressive strengths as well as the failure behaviors of the T-2.5DWC exhibit an obvious strain rate strengthening effect in both the weft and warp directions. In addition, the rate-dependent finite element model developed in this study accurately simulates the compressive modulus and strength of T-2.5DWC along both the warp and weft directions under various strain rates. [ABSTRACT FROM AUTHOR]

The split Hopkinson bar (SHB) has been widely used for testing the dynamic mechanical behavior of materials. However, it is hard to involve complex stress conditions in traditional SHB due to its intrinsic characteristics. The Electromagnetic Hopkinson bar (E-Hopkinson bar) has been recently proposed as a solution. Different from the traditional SHB, the stress pulse of the E-Hopkinson bar is generated directly by the electromagnetic force. Therefore, the stress pulse that loads the specimen can be accurately controlled. With this advantage, some experiments that cannot be done with traditional SHB can be conducted by the E-Hopkinson bar technique. In this review, we introduced briefly the basic principles of the E-Hopkinson bar. Some lasted tests, such as symmetrically dynamic compression/tension of materials, interlaminar fracture of composites, dynamic Bauschinger effect of metals, intermediate strain rate tests, and dynamic multi-axial tests were also introduced. This new technique will be helpful for those researchers in the field of solid mechanics, especially when the strain rate and complex stress condition are involved. [ABSTRACT FROM AUTHOR]

• Dynamic compression test of 2DTBC is enabled using a novel symmetric synchronous dynamic testing technology. • Rate-dependent and direction-dependent compressive failure mechanism of the 2DTBC is elaborated. • Micro-bucking and sub sequential kink band of axial fiber tow dominates axial compression failure. • Transverse compressive failure relies on the accumulation of micro-cracks in the interface and matrix. The effects of loading rate and loading direction on the compression failure behavior of a typical 0°/±60° two-dimensional triaxially braided composite (2DTBC) were studied by compressing brick specimens cut from an eight-layer 2DTBC panel along the axial and transverse directions. Quasi-static tests were conducted using an electronic universal testing machine, and a novel Electromagnetic Split Hopkinson Pressure Bar (E-SHPB) was employed to carry out dynamic tests. High-speed cameras were employed to monitor the progressive failure process in the specimen during the tests, and the failure morphology was examined using an optical microscope. The test results show that both axial and transverse compression strength noticeably increase under dynamic loading conditions. Moreover, different failure mechanisms for the 2DTBC under axial and transverse compression were observed, and the influence of loading rate on the compressive failure behavior of the 2DTBC was systematically investigated. [ABSTRACT FROM AUTHOR]

As a common matrix in fiber-reinforced polymers, dynamic mechanical responses of epoxy resins are crucial for impact resistance design of reinforced polymer composites. In this study, we investigate the ambient temperature sensitivity on the mechanical performance of epoxy resin at various strain rates. Uniaxial compression tests are implemented with a universal machine and a split Hopkinson Pressure Bar (SHPB) both fitted with temperature chambers over various strain rates and ambient temperatures. The test results show that both the elastic modulus and compressive yield strength increase significantly as the strain rate goes up during each constant temperature, and the deformation process reveals the reduction of the plastic deformation localization of the epoxy material at higher ambient temperatures. Besides, the drastic changes are found in the improvement of compressive performance near the glass transition temperature under dynamic loadings. The variation of elastic modulus and yield strength influenced by temperatures and strain rates are analyzed and modeled, respectively. [Display omitted] • Strain rate and temperature dependence on mechanical response of epoxy is studied. • Deformation process and plastic localization of epoxy are characterized. • Rate-temperature sensitivities of mechanical properties are analyzed and modeled. [ABSTRACT FROM AUTHOR]

Highlights • Fiber reinforcement affects the dynamic compressive failure behavior of SFR PEEK composites. • Fiber-matrix interface is the main origin of strain rate sensitivity. • Local heating induced phase transformation presents at the fracture surface. • Fiber distribution affects the rate sensitivity of PEEK composites. Abstract This paper investigates experimentally the dynamic compressive behavior of short fiber reinforced polyetheretherketone (PEEK) composites, with a specific focus on the effect of strain rate, fiber reinforcement and fabrication process. Hopkinson compressive bar system is employed to test the specimens with strain rate varies from 800–2500/s. Ultra-high speed camera system is used to record the deformation and failure process. Scanning electron microscopy (SEM) is introduced to examine the fracture surface, and to analyze the failure mechanism and its rate dependency. Three different types of PEEK composites are studied and compared to investigate the sensitivity of failure mechanism to fiber reinforcement and fabrication method (injection and extrusion). The results indicate that the ultimate stresses of PEEK and PEEK composites present different levels of sensitivity against strain rates, while the failure strain of PEEK composites decrease with the increase of strain rate. The strain rate dependency is associated with the increase of interface toughness under higher strain rate. The experimental results also identify the presence of phase transformation for matrix material during the high-rate compressive failure. The sensitivity of failure behavior against fabrication process is found to associate with the difference of fiber distributions. [ABSTRACT FROM AUTHOR]

The anisotropy and heterogeneity of carbon fiber–reinforced polymer (CFRP) composites contribute to their complex failure characteristics, posing challenges for predicting their impact failure behavior. In this study, high-fidelity finite element models are established to predict the performance of laminated and woven composite panels impacted by a metallic projectile, with consideration of strain-rate effect and impact attitudes. The numerical models are experimentally validated and are applied to investigate the impact resistance of both composites under various impact conditions. The results indicate that the maximum ratio of delamination of laminated panel is about 0.4, which is greater than 0.2 of the woven panel. Woven panels can better withstand impact damage, while laminates are more prone to delamination under high-speed impacts loads. • A mathematical model is developed to calculate projectile attitude for impact test. • The penetrating thresholds of CFRP panels are predicted using an efficient FE model. • Differences on impact failure behavior of laminate and woven panels are clarified. • Effects of projectile attitude on impact resistance of CFRP panels are illustrated. [ABSTRACT FROM AUTHOR]

Dynamic characterization of textile composites is confronted with great challenges due to its large unit-cell size and the inherent limitations in specimen size for the Hopkinson bar-based test system. The small specimen size will inevitably introduce variations in effective mechanical response and failure mechanism, and bring about additional problems in determining the realistic dynamic properties of the material. This work experimentally investigated the dynamic compression behavior of three-dimensional angle interlock woven composite (3DWC) using the split Hopkinson pressure bar (SHPB). Specimens with different sizes were designed to explore the size dependency, strain-rate dependency and orientation dependency for the compressive behavior of the 3DWC. A high-speed camera and an optical microscope were introduced to elaborate on the damage progressing process and fracture morphology under different loading conditions. With an increase in strain rate, the measured strength of warp-direction specimens increased by approximately 7.6%, 4.8%, and 2.6% for three different sizes of specimens, accompanied by more severe intra-tow damage. Different-sized dynamic specimens exhibited comparable failure processes but modest variations in measured properties. When the number of unit cells in a specimen increased from two to three and four, the strength was observed to rise by around 14.9% and 21.9% respectively. In comparison to the warp-direction specimen, the weft-direction specimens exhibited substantially higher strength and failure strain, as well as distinct dominant failure modes of yarns. This work provides valuable insights into the determination of dynamic properties for 3D woven composites, and the designing and interpretation of dynamic test methods. • Obvious size effect and slight strain rate effect of 3D woven composites were found from the compressive mechanical performance in warp direction. • Specimens under different strain rates have approximately same failure sequence. With the increase of size, the appearance time of damage is delayed and the degree of failure is weakened. • The higher strain rate of warp compression load can produce greater local shear stress which tends to cut the undulated warp tows and unbind the compact state of the yarns. • Specimens subjected to weft compression exhibit significantly higher strength and failure strain. The interface damage accompanied with the separation of warp yarns dominates the failure. [ABSTRACT FROM AUTHOR]

The mechanical performance of the fiber tow composite is crucial for textile composites. To characterize the tensile properties of the carbon fiber tow composite, a tensile test methodology for high strain rate loading was developed based on the Split Hopkinson tensile bar equipped with an ultra-high-speed camera. The tensile performance of the tow composites is measured under quasi-static and dynamic loading rates, respectively. Furthermore, the effects of gauge length, fiber counts of specimens and the strain rate sensitivity are investigated. The results indicate that the tensile strength of carbon fiber tow composite is related to the length and fiber counts of the tow specimen and affected by the loading rates. In addition, a modified Weibull model was proposed to evaluate the effects of gauge length and strain rate on the tensile strength of the carbon fiber tow composites. • A test methodology to characterize the dynamic tensile properties of fiber tow composites was developed. • The effects of gauge length and fiber counts of the carbon fiber tow specimen were clarified. • The tensile strength and failure mechanism of the carbon fiber tow composite under different loading rates were revealed. • A modified Weibull model was proposed to describe effects of gauge length and strain rate on carbon fiber tow composites. [ABSTRACT FROM AUTHOR]