Study on the Thermal and Impact Resistance Properties of Micro PA66/PU Synergistically Reinforced Multi-Layered Biaxial Weft Knitted Fabric Composites

In this paper, the influence of micro PA66/PU in multi-layered biaxial weft knitted (MBWK) fabric reinforced composites on thermal and impact resistance was studied. The main objective was to investigate the role of micro PA66/PU in terms of improving material performance. The results showed that the addition of micro PA66/PU improved the thermal stability of the MBWK composite. It is observed that the onset degradation temperatures increased by 1.6°C in thermo-gravimetric analysis (TGA) test and the Tg increased by 2.8°C in the dynamic mechanical analysis (DMA) test. Besides, the impact energy absorption of composites increased by 5.3% after the addition of micro PA66/PU. The addition of micro PA66/PU effectively reduced the impact damage area from the failure morphology after impact. In simple words, the addition of micro PA66/PU effectively improves the comprehensive properties of composites.

Research on the Mechanical Properties and Energy Consumption Transfer Law of Cement Tailings Backfill Under Impact Load

The cemented tailings backfill (CTB), which plays a significant role in the stability of mine structure, is made of cement, tailings, and water in a certain proportion. When blasting and excavating an underground mine, the CTB will be disturbed by blasting. The impact load of blasting has an impact on the stability of the CTB, which is directly related to the safety of mine construction. The mechanical behaviour of CTB is generally affected by the cement-tailings ratio (C/T) and average strain rate (ASR). Therefore, a series of impact experiments were carried out on three CTB specimens with different C/T using a SHPB. Combined with the experimental results, this account reports studies on the effects of C/T and ASR on the mechanical properties of CTB, and on the energy transfer laws of CTB during impact compression. The research results show that when the ASR is less than 70 s−1, the peak stress and the peak strain have the same trend, and both of them continue to increase with the increase of ASR.When the ASR exceeds 70 s−1, as the ASR increases, the peak stress continues to increase, but the peak strain decreases gradually. Afterwards, the law of energy transfer of the CTB specimen was analyzed. It was found that as the incident energy increased, the energy reflection ratio of the CTB increased. Both the energy transmitted ratio and the energy dissipation ratio decreased. The volumetric energy showed a sharp increase first and then a trend Because of the slowly increasing trend. Finally, according to the failure morphology of the CTB, it is found that the ASR and the C/T together affect the failure of the CTB. The failure model of the CTB is mainly split failure and crush failure.

Study on Mechanical Properties and Failure Mechanism of Axial Braided C/C Composite

In order to study the mechanical properties and failure mechanism of the axial braided C/C composites, the microscopic and macroscopic mechanical properties of the composite were investigated. In view of the size effect of the samples, the properties of the samples with different thickness were tested. The strain during loading was measured by optical method, and the failure morphology was observed by SEM. The changing characteristics of stress-strain curve were analyzed, and the failure characteristics of materials and failure mechanism under various loads were obtained. It was found that brittle fracture was observed during the tensile process of axial braided C/C composites, and the main failure forms were fiber rod pulling and partial fiber rod breaking in the axial direction. Radial failure was mainly in the form of fiber bundle fracture and crack stratification propagation. When compressed, the material exhibited pseudoplastic characteristics. The radial compression sample was cut along a 45-degree bevel. The axial compression curve was in the form of double fold, the axial fiber rod was unstable, and the transverse fiber bundle was cut. During in-plane shearing, the axial fracture was brittle and the fiber rod was cut. The radial direction showed the fracture and pulling of the fiber bundle, and the material had the characteristics of pseudoplasticity. The research methods and results in this paper could provide important references for the optimization and rational application of C/C composite materials.

Numerical analysis of strain rate effect on ballistic impact response of multilayer three dimensional angle-interlock woven fabric

This paper investigates the ballistic impact on Kevlar multilayer three-dimensional angle-interlock woven fabric (3DAWF) by proposing the mesoscale geometrical model for the numerical simulation. Multilayer 3DAWF is designed to yarn level configuration by utilizing the membrane elements to reduce computational time and enhance accuracy. The general-purpose finite element code LS-DYNA is employed to predict the ballistic behavior of multilayer 3DAWF under ballistic penetration. The velocity evolution of the projectile, energy absorption mechanism, and failure morphology of multilayer 3DAWF are predicted and validated by the impact test results. It is found that the mesoscale model based on strain rate material models accurately reproduces the ballistic test results. Numerical simulations with strain rate effects in the yarn material properties have a higher precise prediction in the projectile's velocity, energy absorption mechanism, and failure morphology compared with traditional FEA. This study demonstrated the importance of the strain rate effect of material properties in simulating the ballistic impact on the fabric and dramatically improves the ballistic impact simulation's accuracy on fabric.

Experimental Study on Compressive Property of Steel Fiber Recycled Mortar Porous Brick Masonry

From the compression test of steel fiber recycled mortar porous brick masonry, it was researched the effects of different amounts of steel fiber and recycled fine aggregate on compressive strength, failure morphology, elastic modulus, stress-strain law and Poisson's ratio performance. The test value is compared with the calculation formula of ordinary mortar porous brick given in GB 50003-2011.The test showed that the steel fiber recycled mortar porous brick masonry had better compressive strength and deformability.

Experimental investigation of the crush performance of prepreg platelet molding compound tubes

This work presents an experimental study characterizing the crush performance of hollow cylindrical tubes made with prepreg platelet molding compound (PPMC). PPMC is a composite material system that uses platelets from chopped and slit unidirectional prepreg as the basis for a molding compound. This material system has a higher fiber volume fraction and better mechanical properties than traditional short fiber systems and can be molded into complex geometries unlike continuous fiber systems. As such, this material system shows promise for use with complex structural members in vehicles. The failure morphology and specific energy absorption of the material are evaluated with different thickness-to-diameter geometries and test speeds. In addition, this work investigates how PPMC components compare to traditional continuous fiber components and finds that PPMC performs as well as continuous fiber layups with similar effective laminate stiffnesses.

Influence of Temperature with its Geometric and Failure Morphology Defects on the Mechanical Properties of Graphene: Molecular Dynamics Simulation (MDs)

This paper addressed that graphene is a regular monolayer of carbon atoms settled in a 2 D-hexagonal lattice; which is listed among the strongest material ever measured with strength exceeding more than hundred times of steel. However, the strength of graphene is critically influenced by temperature, geometric & vacancy defects (VD). Defects are at all believed to worsen the mechanical toughness and reduce the strength of graphene sheet. They are revealed that stiffness and strength are the key factors in determining solidity and life span of any technological devices. Molecular dynamics-based atomistic modeling was performed to predict and quantify the effect of non-bonded interactions on the failure morphology of vacancy affected sheets of graphene. The defective sheet of graphene containing vacancy defect was simulated in conjunction with the non-bonded interactions experienced due to the presence of a pristine sheet of graphene.

Experimental and Finite Element Research on the Failure Mechanism of C/C Composite Joint Structures under Out-of-Plane Loading

The loading and the failure mode of metal hexagon bolt joints and metal counter-sunk bolt joints of C/C composites were investigated. The joints were tested for out-of-plane loading at two temperatures (600 °C and 800 °C). The failure morphology of a lap plate was investigated, and the main failure modes were determined. The typical load–displacement curve was characterized and the test was simulated using ABAQUS non-linear finite element software. Furthermore, progressive damage was induced, and comparison of the finite element simulation with the experimental data revealed that the failures mainly occurred in the lower lap plate and were dominated by cracking and delamination of the matrix, accompanied by the pull-out of a small number of piercing fibers. Finally, the influences of the temperature, nut radius, and fixture geometry on the critical load were determined via simulation.