Key Engineering Materials Vols. 353-358

Abstract: In this paper, an analysis of fatigue crack growth (FCG) behavior from a statistical point of view has been carried out. Fatigue crack growth tests were conducted on sixteen pre-cracked compact tension (CT) specimens of the pressure vessel (SPV50) steel in controlled identical load and environmental conditions. The assessment of the statistical distribution of fatigue crack growth experimental data obtained from SPV50 steel was studied and also the correlation of the parameter C and m in the Paris-Erdogan law was discussed. The probability distribution function of FCG life and FCG rate seems to follow the 3-parameter Weibull.

Abstract: Successive observation of transgranular small fatigue crack growth behavior of alpha-brass was performed by means of an atomic force microscope (AFM) equipped with small in-plane bending fatigue testing machine. In the low growth rate region after crack initiation, the fatigue crack grew in a zig-zag manner as a result of successive crack branching and deflection. The fatigue crack deflection behavior was investigated by the crystallographic orientation analysis based on the Electron Back Scatter Diffraction (EBSD) technique. The slip factor considering the slip system and singular stress field at the crack tip was introduced in order to evaluate the easiness of slip deformation instead of Schmid factor. The direction of crack deflection was found to be explained well by the slip factor and the geometric relative location between the preferential slip plane and crack front.

Abstract: Dynamic Mechanical Analysis (DMA) and static relaxation tests are carried out to study the viscoelastic deformation of PC/ABS alloy with blending ratio of PC to ABS being 50/50. A modified approach is developed to calculate the relaxation modulus of PC/ABS alloy from the DMA experimental results of storage and loss moduli. Comparison of the results obtained from DMA and static relaxation tests is presented and good agreement is found.

Abstract: ZrW2O8 was successfully synthesized via combustion method with (NH4)5H5[H2(WO4)6] ·H2O, ZrOCl2·8H2O, H3BO3, (NH2)2CO and HNO3. The best prescription of combustion synthesizing of ZrW2O8 was obtained. The linear thermal expansion coefficient of synthesized ZrW2O8 is -5.08×10-6oC-1 in the temperature range of 50-600oC. Different weight ratios of ZrW2O8 and ZrO2 were taken into account. Al2O3 was added into the composite during sintering to increase the density of the composites. When the weight ratio of ZrO2 to ZrW2O8 is 2, the composite with near zero thermal expansion can be obtained. 0.25 wt% Al2O3 can effectively increase the density of ZrO2/ZrW2O8 composites with slight influence on the thermal expansion property.

Abstract: To meet the high reliability of structural design and safety evaluation on carbon fiber wound reinforced polymeric (CFWRP) pressure vessel, the traditional safety factor design was substituted by reliability design based on the reliability theory and statistical principle. Eight CFWRP pressure vessels were manufactured with the same material system by the same winding technique. And experiments were conducted to obtain the probabilistic distributions of design variables. Results derived from reliability design (fiber thickness) agreed well with experimental results and were much lower than that from conventional design. Through comparison among reliability design results with different statistics of fiber strength, significant effect of the variation of fiber strength on structural reliability of composite pressure vessel was demonstrated. The conventional design was verified to be not reasonable since it considers only the mean value of fiber strength without the effect of fiber strength distribution on structural resistance of pressure vessel.

Abstract: A new kind of sealing composite material reinforced mainly with aramid and pre-oxidized fibers were developed by molding preparation method. The effect of different surface treatment methods of the fibers on the heat resistance of the composite material was studied. The optimum prescription of the sealing composite material was obtained by regression design method. The relationship between the transverse tensile strength of the material after ageing at elevated temperatures and its main ingredients was investigated. The performances of the developed sealing composite material were tested, and the results indicate that the main performances of the material coincide with the requirements prescribed in Chinese national standard and some performances are even better than that of the products of some famous corporations.

Abstract: The uniaxial/multiaxial cyclic deformation behaviors of SiCp/6061Al alloy composites with various particulate volume fractions were studied by uniaxial and multiaxial cyclic straining or stressing tests at room temperature. The cyclic softening/hardening features and ratcheting behaviors of T6-treated composites and un-reinforced matrix were discussed in different loading conditions. It is shown that the ratcheting also occurs in the composites under uniaxial and multiaxial asymmetrical cyclic stressing, and the ratcheting strain increases with stress amplitude and mean stress; however, the addition of SiC particulates into the matrix increases the resistance of the composite to ratcheting. The ratcheting depends greatly on the shapes of loading paths and mainly occurs in the direction of non-zero mean stress.

Abstract: The fracture toughness and the fracture energy are obtained on the notched beams in three-point bending according to the RILEM draft recommendation. An experiment is designed to obtain the law on the alteration of the PPFRC’s (Polypropylene Fiber Reinforced Concrete) fatigue life and fatigue strength caused by the fibers. S-lgN curve is plotted according to the experimental data and fatigue is obtained through the Linear Regression. Theoretical analysis of the PPFRC’s bending fatigue characteristic is carried out. The fiber’s influence on the PPFRC’s fatigue behavior is stated and the fiber reinforcement mechanism is discussed. The result shows that the fiber can improve the PPFRC’s fatigue life and fatigue strength. The composition and development of the fatigue strain under the cyclic load are analyzed using experimental data. The law of the fatigue damage accumulation and evolution under cyclic load is studied. A fatigue damage mode, which can be used to predict the fatigue life of the PPFRC, is established.

Abstract: In this paper, a BaPb0.6Ce0.4O3 (BPCO)/Al matrix composite with a good anti-radiation property was fabricated by hot pressing in air for the first time. Differential scanning calorimeter (DSC) and Thermal Gravimetric (TG) analysis of the compacted blended powders were performed in air to study the oxidation behavior, by which the hot-pressing parameters were determined. Transmission electron microscope (TEM) images and X-ray diffraction pattern showed that there was an incomplete reaction between aluminum alloy matrix and BPCO particles during fabrication process. Compared with the aluminum alloy matrix, the X-ray and γ-ray absorption abilities of the composite were increased by 68.05% and 46.63%, respectively.

Abstract: In this work, Ni-Al-Ti-B composite powders with Ni: Al: Ti: B atom ratio of 5.7: 1.9:1:1 were prepared by using mechanical activation (MA) method. The MA processes were performed by vibration ball mill in a water-cooled chamber for 30 h. The ball-to-powder weight ratio was 10:1. In order to reduce the oxidation of the powders during milling process, ball milling was performed under an Argon atmosphere. The evolution of morphology and microstructure of Ni-Al-Ti-B composite powders were examined at different milling stages using scanning electron microscope and X-ray diffraction. Distribution of powders size was analyzed and the results showed that there were three stages for the change of powders size: (1) at the first stage, powders size increased due to more welding than fracture of the powders within 2h of MA, (2) at the second stage, particle size continuously decreased until 16h of MA due to more fracturing than welding, and (3) after 16h of MA, the particle size remained constant when welding and fracture reached an equilibrium. Calculation results according to Scherrer equation from X-ray pattern showed that the effective grain size continuously decreased with MA time. X-ray diffraction pattern confirmed that the formation of Ni and Ti solid solution during MA process of the Ni-Al-Ti-B composite powders.