Key Engineering Materials Vols. 452-453

Abstract: This paper discusses a stochastic microscopic stress analysis of a composite material for a microscopic random variation. The stochastic stress analysis is performed via a stochastic homogenization and multiscale analysis. The homogenization method is employed for the multiscale analysis and the Monte-Carlo simulation or perturbation-based method can be employed for the stochastic analysis. In this paper, outline of the analysis and some numerical results are provided.

Abstract: The continuous basalt fiber (CBF) as inorganic fiber obtained from the basalt melt. It has high elastic modulus, low bulk density, low thermal conductivity, low moisture absorption rate and excellent alkali resistance, etc. In this paper, the split Hopkinson pressure bar (SHPB) technique is used for testing the CBF composite plate and its sandwich structure with aluminum foam core dynamic mechanical properties, and then to study the dynamic properties of CBF composite plate and its aluminum foam sandwich structure under different high strain rate. From the test results we can see that the CBF-foam aluminum sandwich structure has superior energy absorption properties, and also from the experiment results we can obtain that the sandwich structure dynamic stress-strain curves has a typically "three-phase" characteristics and strain rate effect.

Abstract: Notched compact tension specimen of 304 stainless steel (0.8CT, notch tip radius of 1mm, thickness of 6mm) was low-cycle-fatigued at room temperature at stress ratio of -1 in 99.9999% H2 and in pure air at 1 and 0.1 Hz at apparent stress intensity factor of 34.4MPa . The H2 acceleration of both crack initiation and growth at notch is significant: 3-4 times faster than pure air. The accumulated plastic zone was analyzed by the recrystallization technique. It is shown that the accumulated plastic zone in H2 is smaller than in pure air.

Abstract: Using a fatigue testing method by which fatigue cracks can be initiated and propagated in a film adhered to cover a circular through-hole in a base plate subjected to cyclic loads, annealed copper films of 100m thickness with different crystal grain sizes were fatigued. The fatigue crack propagation in the film with large grains was often decelerated, so the crack propagation rate of the film with the large grain was lower than that of the film with the small grain. When the crack propagation was decelerated, the crack opening displacement obtained from the film with large grain size was smaller than that obtained from the film with small grain size. The relationship between the fatigue crack propagation rate and the stress intensity factor estimated from the crack opening displacement was identical for the cracks in the film with the large grain and the small grain.

Abstract: In this paper, crack growth of thin-walled cylinders containing an initial crack under acoustic plane wave is analyzed. A coupled air-structure modeling is considered for the analyses. For this purpose, a methodology for computational modeling of the fatigue crack growth in cracked cylinders using finite element method is presented. Effects of various parameters such as crack length increment and boundary conditions on the crack growth rate are investigated.

Abstract: To establish clinical bone assessment for osteoporosis, it is necessary to evaluate not only bone density but also trabecular bone microstructure and mechanical properties of bone. Therefore relationship between the micro-structural parameters and the mechanical properties of the cancellous bone of bovine distal femur was investigated. Compression test was carried out using universal testing machine to measure Young’s modulus and the ultimate strength. X-ray CT was used to obtain 3D image of specimens. Bone trabecular orientation was obtained from fabric ellipse by the MIL (Mean Intercept Length) analysis. Young’s modulus and ultimate strength had a high correlation with bone density respectively; furthermore ultimate strength had a high correlation with Young’s modulus.

Abstract: The non-crimp fabric (NCF) have an advantageous combination of high material properties and low cost for processing, and overcomes the disadvantages of the crimp factor of woven fabrics, providing full use of modulus and strength of reinforcing fibre. For using NCF, different stitching tension and thread of non-crimp fabrics may cause the mechanical properties of CFRTP. In this study, it is aimed to clarify the effect of stitching tension and thread of non-crimp fabrics on tensile strength of CFRTP. The disorder degree of the thickness direction in the fibre bundle and the ratio of resin rich area were examined by the SEM image analysis. There is the inverse correlation between tensile strength and the disorder degree to the thickness direction in the fibre bundle.

Abstract: Light weight aluminum alloy honeycomb materials are ideal lightweight structure materials, which have higher specific strength and stiffness, and widely applied in aviation, aerospace, automobile and so on, and also it is an ideal material for damping, buffering, heat insulation and energy absorption. In this paper, the SHPB technique which the aluminum alloy bar diameter is 37mm is used for studying the dynamic mechanics property of the lightweight aluminum alloy honeycomb materials which the diameter is 30mm, and then to study the dynamic mechanical properties of the material, from the results we can see dynamic strain-stress curves can be divided into three phases, elastic phase, stress platform and compaction phase. And the numerical simulation method was used for study the dynamic deformation process of the honeycomb panel material under impact load, and also compare the results with the specimen cell figures which were observed by the microscope.

Abstract: This paper discuses the development of the optical sensor due to detect the micro crack and measure the surface property of the contact surface in the equipment. To measure the surface property is an index for detecting no uniformity contact and / or micro crack on the contact surface. So, there is demand of the development of the sensor to measure the surface property in using equipment. This sensor has two optical systems, called stylus and skid, to reduce the influence of vibrations on the measurement result. The stylus measures the surface property with the vibration, and the skid measures only the displacement between the sensor and the objective surface at the same place as the stylus, i.e. the vibration. Therefore, the stylus signal minus skid signal shows the surface property. In this research, the proposal of the principle of this system, the methods of the development and the evaluation of the stylus system of the sensor and the development of prototype sensor is described.

Abstract: Environmentally friendly green composites were fabricated from a natural cellulosic fiber (MAO fiber) and a biodegradable starch-based resin through hot-pressing. The effects of fiber length and alkali surface treatment on mechanical properties of the green composites were investigated. Fiber lengths of 2.5, 5, 10, and 20 mm were used and fiber weight content was adjusted to 56%, to obtain short fiber composites with random orientation. Ultimate tensile strength increased with increasing the fiber length up to 10 mm and remained almost constant for further increases in fiber length. Fracture strain for the composites fabricated with fiber length of 2.5 mm showed the smallest value of approximately 2 %, which is less than that of MAO fiber. This might be attributed to the debonding at the fiber/matrix interface. Fracture strains of the green composites with fibers longer than 2.5 mm were almost constant and were comparable to the fracture strains of MAO fiber indicating that the fracture properties were controlled by the fiber. Both tensile strength and Young’s modulus values were increased by alkali surface-treatment for MAO fibers. The reason for this behavior seems that alkali treatment increases the fiber/matrix interfacial adhesion strength primarily by removing lignin.