Applied Mechanics and Materials Vol. 782

Abstract: This study investigates the ballistic penetration performance of aramid fabric impregnated with shear thickening fluid. The ballistic test was conducted at impact velocity of 445 m/s, and three types of shear thickening fluids prepared with silica particles of different sizes (200nm, 340nm and 480nm) are involved. The results demonstrate an enhancement in ballistic properties of fabric due to the impregnation of shear thickening fluids. The fabrics with smaller particle size show better ballistic performance. Microscopic observation of aramid fabric reveals that shear thickening fluids with smaller silica particles have a better adhesion on and between yarns, enhancinging the coupling effect between yarns. The corresponding mechanism was discussed in the paper.

Abstract: Resistance spot welding is used extensively in auto industry. Every commercial vehicle has 4000-5000 spot welds. The weld ability, performance, and reliability are therefore important issues in design. In this paper, we studied weld nugget formation and failure behavior of three-sheet 5052 aluminum alloy resistance spot welds. The Peltier effect between the Cu-Al (the electrode and the Al worksheet) to the nugget formation was noticed. The mechanical strength and fracture mode of the weld nuggets at the upper and lower interfaces were studied using tensile shear specimen configuration. Three failure modes were identified, namely, interfacial, mixed, and pull-out. The critical welding time and critical nugget diameter corresponding to the transitions of these modes were investigated. Finally, an empirical failure load formula for three-sheet weld similar to two-sheet spot weld was developed.

Abstract: To reveal the anti-penetration mechanism of titanium alloys armor quantitively, the volumes of the front crater region, the ductile hole-enlargement region, as well as the back caving region of Ti-6Al-4V alloy and β20C alloy were measured via 3D Optical scanning technology. The experimental results show that β20C alloy, of which the volume fraction of ductile hole-enlargement region is 51%, 10% larger than that of Ti-6Al-4V alloy, presents a better ballistic performance. It is found that the ballistic performance is closely related to the volume of ductile hole-enlargement region and a relatively larger ductile hole is beneficial to improve the ballistic performance. However, the ballistic performance shows no improvement with increasing the volume of front crater region.

Abstract: This paper presents a new energy approach based on the concept of a volume stain-energy-density factor useful to deal with the general problem of brittle fracture for sharp V-notches under mixed-mode I and II. The basic assumption is that the fracture occurs when the volume strain energy density factor arrive at its critical value in the direction of crack initiation where the deviator strain energy density factor is minimum. The method is validated taking into account experiment data already reported in the literature and the analytical predictions are in good agreement with experiment data. It indicates that the accuracy of the new approach is undoubtedly very satisfactory and can be applied in engineering.

Abstract: Resistance spot welding is used extensively in auto industry. Every commercial vehicle has 4000-5000 spot welds. The weld ability, performance, and reliability are therefore important issues in design. Tensile-shear tests are normally performed to evaluate the weld quality and acquire the mechanical strength of spot welds. However, different industry test standards often specify different dimensions for the tensile-shear specimen. In this work, we investigate the failure load and energy absorption of the spot welds made of Q235 steel using tensile-shear specimens of different dimensions. The objective is (a) to determine a specimen dimension independent geometry for failure strength, and (2) to call attention to the deficiency of some of the test standards.

Abstract: Taking bridge structures in service period as research objects, durability experimental method of reinforced concrete (RC) components strengthened with fibre reinforced polymer (FRP) under time-varying hot-wet environment and random fatigue load coupling/interaction was discussed and corresponding experimental system of structural components was developed and integrated. To prove the effectiveness and feasibility of the experimental method proposed, durability/environmental fatigue experiments of RC beams strengthened with carbon fibre laminates (CFL) were carried out including the following four experiments: a) non-interaction experiments (the current method) of constant temperature, constant humidity and fatigue loads, b) interaction experiments of constant temperature and humidity and fatigue loads, c) interaction experiments of real service environment and fatigue loads, d) interaction experiments of real service environment and vehicle random loads. The results showed the durability/environmental fatigue experimental method proposed by this paper was effective and feasible.

Abstract: It is an inevitable phenomenon that flash is generated in the process of hypervelocity impact. The research on impact flash is of important significance for assessing the collision between space debris and spacecraft, identifying the material properties on the surface of planet, evaluating the damage of weapon system. A measurement system was built in order to acquire flash spectrum ranging in wavelength from 200 to 1100nm. The relationship between flash intensity and impact velocity was studied. The spectrum consists of line spectrum and continuous spectrum. Line spectrum mainly concentrates in the range of 200-500nm. The spectral lines of the elements were identified. The strong flash happens within 2.2ms after beginning to impact. In addition, the electron temperature of plasma produced in hypervelocity impact is calculated by spectral method, and compared with the temperature measured by Langmuir three probes.

Abstract: Polyvinyl butyral (or PVB) is commonly used as interlayer in architectural laminated glass and windshield in automobiles for its strong binding, optical clarity, adhesion to many surfaces, toughness and flexibility. A modified in-situ Hopkinson bar system is used to measure the tensile properties of the PVB with the strain rates of 30~100 s^-1. In this system, a high impedance striker tube with the rubber pulse shaper is use to generate a long loading pulse of 50ms. Two X-cut quartz piezoelectric force transducers are sandwiched between the specimen and two bars respectively to directly measure the dynamic loading forces, and the strain field of the specimen is calculated by the Digital Image Correlation (DIC) method via photos obtained by the high speed camera. The local deformation of the full-field specimen was clearly displayed and the fracture strain of the specimen was evaluated. The results show that the tensile strengths of the PVB increase with increasing loading strain rates.

Abstract: The era of high speed railway has come and the most important issue of the high speed train is the safety, which is directly related to billions of families. One of the most serious threats to the safety of the high speed train is the vibration of train body at curve track, which may cause the train off the track. Semi-active vibration control method is a possible solution compared with active control method which has robust problem and passive control method which has efficiency issue. Magnetorheological technology is a typical semi-active vibration control method which has been widely used in the automobile, architectural construction and aerospace. The high speed train using magnetorheological technology has not been fully investigated especially for the dynamic performance at curve track. In this paper, a high-speed train model with MRF dampers is simulated by a combined ADAMS and MATLAB simulation. The dynamic performance of high speed train operating at different speeds and turning radius is investigated to reveal the mechanism of how the MRF damper affects the train’s stability and vibration. The results show that the semi-active suspension installed with MRF dampers substantially improves the stability and dynamic performance of the train at curve track.

Abstract: In this paper, by the large scale borehole soundless cracking method, the fracture experiments were performed on the plain concrete and reinforced concrete. For plain concrete experiment, the open borehole was prefabricated in the concrete pillar at first. Secondly, two non-woven fabric bags contained soundless cracking agent were prepared, one for the main expanding and the other for blocking. Thirdly, the main expanding bag was plugged, and then the blocking bag. At last, the cracks in the concrete pillar were developed within 3 hours. For reinforced concrete experiment, the closed boreholes were prefabricated in the concrete beam. First the strain gauges were pasted on the designed locations of the stirrups. Secondly, the boreholes were filled with expanding grout and closed by the flange. The beam was cracked afterwards, and the strain was measured by the test system. It is proved that the large scale borehole soundless cracking method on the concrete members is practicable.