Chenguang Huang

Microstructure and mechanical behaviour of a SiC particles reinforced Al-5Cu composite under dynamic loading

The mechanical behaviour of a composite of Al–5Cu matrix reinforced with 15% SiC particles was studied at different strain rates from 1×10−3 to 2.5×103 s−1 using both a conventional universal testing machine (for low strain-rate tests) and a split Hopkinson bar (for tests at dynamic strain rates). Whilst the yield stress of the composite increases as the strain rate increases, the maximum flow stresses, 440 MPa for compression and 450 MPa for tension, are independent of strain rate. The microstructures and defect structures of the deformed composite were studied with both scanning electron microscopy and transmission electron microscopy and were correlated to the observed mechanical behaviour. Fracture surface studies of samples after dynamic tensile testing indicates that failure of the composite is controlled by ductile failure of the aluminium matrix by the nucleation, growth and coalescence of voids.

Stiffness behaviour of injection moulded short glass fibre/impact modifier/polypropylene hybrid composites

The stiffness behaviour of injection moulded short glass fibre/impact modifier/polypropylene hybrid composites has been investigated in this work by theoretical predictions and experiments. Predictions from the self-consistent method were found to be in good agreement with test results for the impact modifier/polypropylene blends. By taking into account of the fibre orientation distributions in the skin and core layers, the values of Youngs modulus for the skin and core layers were predicted by employing Eshelbys equivalent inclusion method and the average induced strain approach. The prediction of the values of Youngs modulus for the whole sample was obtained by applying the simple mixture theory of laminated composites to the predicted results for the skin and core layers. Good correlation between predicted and experimental Youngs modulus values were found.

Deformation characteristics of Ti–24Al–14Nb–3V–0.5Mo alloy during hot compression

Abstract Hot compression tests on samples of the Ti–24Al–14Nb–3V–0.5Mo alloy have been done in the ( α 2 + β ) phase field. It has been found that the Ti–24Al–14Nb–3V–0.5Mo alloy has good hot workability and hot compression can be applied satisfactorily to deform the alloy within the temperature and strain-rate ranges of 1030–1130°C and 0.001–0.1 s −1 to ∼50% height reduction. The compressive flow stress varied from 13 MPa over the range of conditions used. The compressive pressure required for deformation is strongly dependent on the temperature and the strain-rate. A strain-rate sensitivity exponent ( m ) of 0.263 and a deformation activation energy of 602 kJ mol −1 are obtained for the conditions used. It is considered that the deformation mechanism of the Ti–24Al–14Nb–3V–0.5Mo alloy in the ( α 2 + β ) phase field involves a combination of dynamic recovery and grain-boundary sliding. An empirical power-law equation valid over the range of temperatures and strain-rate investigated has been developed, the equation accurately describing the temperature and strain-rate dependence of the flow stress.

Failure mechanisms of a SiC particles 2024Al composite under dynamic loading

Dynamic mechanical response of a 20 vol% silicon carbide particles (SiCp) reinforced 2024 Al composite prepared by powder metallurgy techniques were studied with a split Hopkinson bar. The fracture mechanisms and the deformation microstructure were examined with Scanning Electron Microscopy (SEM) and Transmission Electron Microscopy (TEM). The present results indicate that the composite has a strong SiC-Al interfacial bonding; failure of the material is mainly caused by fracture of SiC particles and tearing failure of the SiC-Al interface. This failure by interface tearing with adhesion of an aluminium layer on SiC particles on the fracture surfaces has not been reported in SiC particle-reinforced aluminium composites. High-resolution transmission electron microscopy studies showed that many of the SiC-Al interfaces have coincident site lattice structures, which are considered to make a significant contribution to the strong interfacial bonding.

High temperature compression of Ti3AlNbVMo alloy

Abstract Samples of Ti 24Al 14Nb 3V 0.5Mo alloy were hot compressed in the α 2 + β phase field. It was found that Ti 24Al 14Nb 3V 0.5Mo alloy has good hot workability and no cracks were found on the billet surfaces. The compression flow stress varied from 13 MPa to 128 MPa over the range of conditions used. The compression pressure required for deformation is strongly dependent on temperature and strain rate. The experimental results show that hot compression can be applied satisfactorily to deform the Ti 24Al 14Nb 3V 0.5Mo alloy within temperature and strain rate ranges of 1030–1130 °C and 0.001–0.1 s −1 to about 50% height reduction. A strain rate sensitivity exponent m of 0.263 and a deformation activation energy of 621 kJ mol −1 were obtained for the compression conditions used and it is considered that the deformation mechanism of Ti 24Al 14Nb 3V 0.5Mo alloy in the α 2 + β phase field involves a combination of dynamic recovery and grain boundary sliding. An empirical power law equation valid over the range of temperatures and strain rates investigated was developed. The equation describes accurately the dependence on temperature and strain rate of the flow stress.

Real-Time Observations on Deformation and Failure of LY12 Samples under Impact Tension

In this paper, the real-time deformations and failures of LY12 samples loaded by an SHTB are investigated by an optical system, which consists of a high-speed camera, a flash lamp, a frame grabber and a synchronization device with the controlling accuracy of 1 microsecond. The deformation history of LY12 is obtained with a time interval of 10μs and the result is compared with that acquired by classic Hopkinson method at the same time. Besides, two different failure modes and the crack propagation velocity of LY12 specimen are detected in impact tensile process. The fracture textures after working are also surveyed by SEM and it shows that the dynamic fracture mode is affected by the microstructure of materials.

Experimental Study on Dynamic Properties of High Strength Fiber Clusters

In this paper, the dynamic behaviors of several kinds of high strength fibers, including Kevlar, UHMPE, glass fibers, carbon fibers etc., are investigated experimentally, with a Split Hopkinson Tension Bar（SHTB）. The effect of strain rate on the modulus, strength, failure strain and failure characteristics of fibers, under impact loading, is analyzed with the relative stress vs. strain curves. At the same time, the mechanism about the rate dependence of mechanical behaviors of various fibers is discussed based on the understanding on the microstructures and deformation models of materials. Some comments are also presented on the decentralization of experimental results, and a new method called traveling wave method is presented to increase the experimental accuracy. Research results obtained in this paper will benefit to understand the energy absorption and to build up the constitutive law of protective materials reinforced by high strength fibers.