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This study investigates the mechanical properties of polypropylene fiber-reinforced foamed concrete (PPFRFC) under high strain rates and large compressive deformation, focusing on the effects of varying fiber contents and lengths. Results show both peak and plateau stress increase with fiber content, reaching a maximum at 1.5 wt.% before decreasing. Similarly, increased fiber length enhances both stresses, but beyond 9 and 14 mm, they decline. The dynamic increase factor is sensitive to fiber content and length, with the lowest values observed at 1.5 wt.% content and 9 mm or 14 mm length. Failure mode analysis shows that as fiber content increases, damage extent decreases, with fewer fragments. At 1.5 and 2.0 wt.%, specimens largely retain their overall contour after impact, while fiber length has a smaller effect on failure mode. [ABSTRACT FROM AUTHOR]

Nickel-based superalloys show high strength retained also at high temperature and they are widespread used for structural components exposed during services to high temperature combined with high strain rate or impact loading conditions. The objective of this study was the investigation of the plastic flow behaviour of Laser Metal Deposited Nickel-based superalloy Inconel718. The material was manufactured at Northwestern Polytechnical University in China. Specimens with three different heat treatment conditions were investigated: as-deposited, directly aged and aged after homogenization and solution. High strain rate tensile tests were performed on the direct Hopkinson bar setup developed at DYNLab laboratory at Politecnico di Torino. At a nominal strain rate of 1500 s-1 the temperature sensitivity was investigated between 20 and 1000°C. An induction heating system was adopted, and the temperature was monitored by thermocouples and infrared pyrometer and high-speed camera. The results showed the materials strength decreases as a function of temperature with a significant drop starting from 800 °C. An asymmetric tension-compression behaviour was found by comparing the results with data in compression. The strain rate influence was investigated at room temperature and very limited or negligible sensitivity was found covering six orders of magnitude in strain rate.

Theoretical and experimental studies on the compressive mechanical behavior of 4-harness satin weave carbon/epoxy composite laminates under in-plane loading are conducted over the temperature range of 298–473 K and the strain rate range of 0.001–1700/s in this article. The stress–strain curves of 4-harness satin weave composites are obtained at different strain rates and temperatures, and key mechanical properties of the material are determined. The deformation mechanism and failure morphology of the samples are observed and analyzed by scanning electron microscope (SEM) micrographs. The results show that the uniaxial compressive mechanical properties of 4-harness satin weave composites are strongly dependent on the temperature but are weakly sensitive to strain rate. The peak stress and elastic modulus of the material have the trend of decrease with the increasing of temperature, and the decreasing trend can be expressed as the functional relationship of temperature shift factor. In addition, SEM observations show that the quasi-static failure mode of 4-harness satin weave composites is shear failure along the diagonal lines of the specimens, while the dynamic failure modes of the material are multiple delaminations and longitudinal splitting, and with the increasing of temperature, its longitudinal splitting is more serious, but the delamination is relatively reduced. A constitutive model with thermomechanical coupling effects is proposed based on the experimental results and the increment theory of elastic–plastic mechanics. The experimental verification and numerical analysis show that the model is shown to be able to predict the finite deformation behavior of 4-harness satin weave composites over a wide range of temperatures. [ABSTRACT FROM AUTHOR]

• A novel impact fatigue device based on the split Hopkinson pressure bar. • A novel method to achieve repeated impact loading with constant amplitude. • The method has the advantages of controlling loading waveform and monitoring load. • The loading rate has a significant effect on the fatigue life of Ti-6Al-4 V. The lack of reliable testing methods and standards hinders systematic research on the impact fatigue performance of materials. The aim of developing an impact fatigue test method is to generate repeated impact loads with a constant amplitude, which is difficult to achieve using various existing impact test devices. This study investigated the principles of cyclic loading-resetting and constant-amplitude loading based on the split Hopkinson pressure bar (SHPB) system, established a novel impact fatigue test device, and verified the developed method by testing the impact fatigue life of a Ti-6Al-4V alloy. Electromagnetic valves, laser sensors, and a vacuum pump were used in the developed device to launch and reset the striker bar; a servo motor and laser sensors were used to reset the loading bars and specimen, and the entire system was controlled by a programmable controller to achieve continuously repeated loading. To achieve constant-amplitude loading, the conditions required to ensure that the specimen moves away from the incident bar before the returning stress wave reloads the specimen was derived. It was found that a constant-amplitude repeated impact on the specimen could only be achieved through the precise design of the geometric configuration and material of the loading bars. This method is considerably simpler than various existing methods based on energy absorption and is more applicable to impact fatigue tests. The verification tests showed that the highest loading frequency of the device was 0.5 Hz, the loading rate exceeded 105 kN/s, and the amplitude error of the repeated impact loads did not exceed 2.45 %. Under loads with the same amplitude, the impact fatigue life of a Ti-6Al-4V alloy was considerably shorter than the non-impact (low strain rate) fatigue life, which indicates the necessity of investigating the strain rate effect on the fatigue performance of materials. [ABSTRACT FROM AUTHOR]