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The SHPB loading three-point bending specimen is a popular way for measuring the dynamic fracture toughness of the material. The wedge shapes on the loading end of the incident bar have necessary effects on the propagation of the stress wave. The dynamic mechanical response and the fracture toughness of the aluminum alloy were measured by SHPB with different wedge shapes, and the influences of wedge shape on determination of dynamic fracture toughness was analyzed in this study. The investigation result can be used to provide reference for the design of a new Hopkinson apparatus for dynamic fracture testing.

At higher loading rates, modified Hopkinson pressure bar apparatus is widely used to determine the dynamic fracture toughness of the engineering materials. For accurate measurement of the dynamic fracture properties, we need to thoroughly understand the contact situation of the three-point bend specimen, with the loading apparatus. Strong inertial effects complicate the specimen’s contact situation with impactor and supports. In this work, ANSYS software is used for modeling and analysis of a modified Hopkinson pressure bar loaded fracture experimental setup. Analysis of stress contours and nodal displacements are used for the examination of specimen contact state. The results indicate that during loading in the elastic range, the specimen remains in contact with the loading apparatus as this is previously proved experimentally.

In order to obtain characteristic parameters of the debris from accident pictures for traffic accident reconstruction, MATLAB image processing technology was applied to deal with accident pictures such as grayscale transformation, binarization, noise reduction and segmentation. According to the proportional relationship obtained by camera calibration between pixel and the actual size, the diameter of sphere debris, the length and width of rectangular debris were achieved. The error calculated by comparing extraction parameters of accident picture with real size is within 5%.

The dynamic fracture behavior of 7075-T6 aluminum alloy was studied by finite element method to simulate a cracked three-point bending specimen loaded by stress wave loading. In order to determine the elastic-plastic dynamic fracture toughness using quasi-static fracture mechanics theory, the nominal load measured by Hopkinson pressure bar loaded fracture testing system was input into a finite element program to calculate the loading point displacement, and then this displacement was employed to obtain the load-displacement field in the vicinity of the crack tip without the inertia effect, the variation of J-integral as a function of time was established using the load-displacement parameters determined by finite element analysis. The critical J-integral corresponding to crack initiation time detected by a small strain gauge mounted on the three-point bending fracture specimen is determined as an elastic-plastic dynamic fracture toughness (JId). The comparison between the equivalent dynamic fracture toughness(KId) given by the aforementioned procedures and the value measured in previous studies was made to verify the validation of the proposed procedure.

Some fundamental issues, such as stress wave dispersion effect, loss of contact, pulse shaping effect are still needed to thoroughly understand in Hopkinson pressure bar loaded fracture experimental techniques. In order to avoid the influence of stress wave dispersion on the analysis of dynamic experimental results, a computational procedure has been developed based on the combined analytical solution of Pochhammer-Chree with Fourier spectroscopy analysis. The validity of this proposed computational procedure was confirmed via the comparison with the experimental stress pulses obtained from pulse-shaped tests. The experimental results can be easily interpreted and the testing accuracy can be improved using this computational procedure.

The SiC/Cu composite is one of the "structural-functional" materials. It shows good mechanical properties and very high thermal, high electrical conductivity etc. But the co-dispersion, wetting and bonding between SiC and Cu interface are of practical importance in the preparation of SiC/Cu composites. In this work, surface treatment techniques such as high-temperature oxidation, acid dipping and alkaline wash were adopted separately on silicon carbide particles, in order to improve the wettability and physical and chemical compatibility between silicon carbide and copper, then we used the replacement reaction method and decomposition-reduction reaction method to generate Cu coating on the surface of silicon carbide. The results shown that, the surface of silicon carbide particle which treated by alkaline wash was cleaner and more rough than that only treated by high-temperture oxidation, moreover, the specific surface of the particle was increased, which resulted in a compact layer of Cu coating. for the same silicon carbide particles, the effect of the Cu coating prepared by decomposition reaction method was better than that by reduction reaction method.

CBN particles coated with borosilicate glass-aluminum composite coating (Glass-Al-CBN) were prepared by a multilayer coating method. The coated composite particles were sintered at 800°C for 2h. XRD, DTA-TG, SEM techniques were used to characterize the samples. It was found that AlN was formed by the reaction of Al and CBN. The mechanical properties and the oxidation resistance of the composite was improved due to the presence of the glass coating and alumina.

The effect of specimen width on the contact state between the three-point bending (TPB) specimen and supports has been investigated with the apparatus of Hopkinson pressure bar using the analysis method of the propagation of stress wave. The results indicate that, the time for loss of contact decreases linearly with the increase of specimen width when the specimen width is less than a critical value, and the relationship between the time for loss of contact and the specimen width shows a parallel line to the abscissa when the specimen width is greater than the critical value.

Sensor data are the basis for health assessment of complex structural systems. Careful selection and logical layout of sensors is critical to enable the high reliability of system health assessment. This paper presents a methodology how to use a minimum number of sensors, and what locations of them should be placed, so that the voltage signals received from the sensor can be used to detect both presence and extent of damage. In this study, an optimization procedure is developed using Genetic Algorithm (GA) to determine the location of piezoelectric sensor for damage detection in a composite wingbox. A new damage index using all differences in voltage signals decomposed by wavelet transform is proposed. Results show that the proposed method is available at determining number and location of sensors for structural damage detection using piezoelectric patch sensors.

The paper presents an effective damage detection method of complex composite structures. It can be carried out through the experimental modal analysis of the damaged structure. The method using the improved Cross Modal Strain Energy (CMSE) technique and Niche GA has many advantages compared with other damage detection methods. The CMSE method can use any modes of the structure and the modes don’t need to be normalized or consistent in scale. The Niche GA improves the efficiency of the calculation and enhances the capacity of identifying structural damage localization. The model is the composite material airfoil case. The numerical results show that the method proposed in this paper is successful for damage detection of complex structures.

A vibration-based approach to detect crack damage in a cantilever composite wingbox is studied using the improved Hilbert-Huang Transform (HHT). The improved HHT is composed of HHT with Wavelet Packet Transform (WPT) and a simple but effective method for intrinsic mode function (IMF) selection. For different damage status, in order to obtain structural dynamic responses, which imply plentiful damage information, the composite wing boxes were excited by a contrived square wave signal. Then, the dynamic responses of intact wingbox and damaged wingbox are disposed using improved HHT. Finally, a feature index vector of structural damage, i.e. the ariation quantity of instantaneous energy, is constructed. The obtained results show that the proposed damage feature index vector is more sensitive to small damage than those in traditional signal processing.