Advanced Materials Research Vols. 197-198

Abstract: This paper studies the effects of temperature and crack tip constraint on cleavage fracture toughness of the weld thermal simulated X80 pipeline steels. A large number of fracture toughness (as denoted by CTOD) tests together with 3D finite element analysis are performed using single edge notched bending (SENB) and tension (SENT) specimens at different temperatures. Coarse-grained heat-affected zone (CGHAZ) is considered as the material microstructure in preparation of the weld thermal simulated fracture mechanics specimens.

Abstract: Mechanical components are subjected heavy alternate load in industries, such as engine crankshaft, wheel axle, etc. The fatigue failure happens after a long work loading, which affects the production cost, safe and time. So the fatigue life predication is fundamental for the mechanical components design. Especially, it is very important for heavy, high-speed machinery. In this paper, both main fatigue life predication formulas are introduced briefly, including Manson-Coffinn formula and Damage strain model. Then, shortages of above life predication formulas are pointed out, and coefficients are explained in detail. Further calculation error analysis is conducted on the basis of experiments on 16 materials. Results show that above life predication formulas lack calculation accuracy. Finally, it is pointed out that coefficients of fatigue life predication formulas are dependent of material performance. So it is unreliable that coefficients are constants for Manson-Coffin and Damage strain model.

Abstract: The fractographic appearance, microstructure, chemical elements and hardness of the pitman shaft of automotive steering gear were analyzed. The fracture is induced by improper heat treatment and non-taking anti-carburization measures on thread part. Some feasible measures, including copperizing, coating anti-carburization paint and keeping localized manufacture allowance, were proposed for preventing the occurrence of similar fractures.

Abstract: Z-pins reinforced 2D ceramic matrix composites (CMCs), integratedly designed new materials, are developed to enhance 2D CMCs through-thickness in the form of Z-pins and to ensure significant increase in interlaminar fracture toughness, delamination resistance and impact resistance, and Z-pins reinforced 2D CMCs have much application. Finite element method was adopted to analyze stress distributions of Z-pins reinforced woven CMCs; the interlaminar shear tests were employed to measure interlaminar shear strength; fractographies were observed to examine failure mechanisms. The results are shown as the following: the insertion of Z-pins reduces concentrated stress fields and enhances the uniform stress distribution on the expected fracture plane. Interlaminar shear strength of Z-pins reinforced woven CMCs is increased as Z-pins insertion reaches a certain number. Interlaminar shear strength goes up with the rise of the number of inserted Z-pins. Z-pins shearing and fabric/matrix debonding are interlaminar failure mechanisms of Z-pins reinforced CMCs.

Abstract: Because the temperature of heat medium in thermal recovery wells is very high, and casing is heated during steam injection process, which has become the main reason of casing failure. Therefore, it is very important to analyze crack propagation and casing failure under thermal mechanical coupling. Three-dimensional finite element model is investigated; geometry model is constructed with native and parasolid method in ADINA. The casing is modeled by native method and strata are modeled by parasolid method, casing are subtracted and merged with strata by Boolean Operation. Gravity and displacement loads are defined in structure model, and temperature load in thermal model. In structural model, casing is treated as thermoplastic material, and strata are treated as hot isotropic material. In thermal model, all materials are treated as heat conduction material. Thermal-mechanical coupling is calculated with the thermo-mechanical coupled analysis solver in ADINA, and casing damage process is calculated. According to the calculating results, the mechanism of casing damage is analyzed.

Abstract: Hydrogen permeation and embrittlement behavior of hot-dip galvanized steels with different sulphite sediment on surface exposed to stimulant marine atmospheric environment was investigated by hydrogen permeation current measurement using modified Devanathan-Stachurski cell, slow strain rate tensile test and scanning electron microscopy technique. The results indicated that hydrogen permeation curves were increasing along with the sediment rising gradually. On the other hand, it was found that hydrogen absorption was accelerated by the cathodic protection of scratched steel surface afforded by zinc coating. Hydrogen absorption and permeation reduced the percentage elongation after fracture of galvanized steel specimens; meanwhile, the fracture characteristics of samples fringe occurred some lacerated phenomena, i.e., galvanized steels show a higher susceptivity of hydrogen embrittlement when exposed to marine atmospheric environment with sulphite.

Abstract: The dynamic responses of the standard charpy impact machine are experimentally studied using the relevant data acquisition system in order to obtain the impact response. For this reason, strain gauges were connected to the data acquisition set and it was then attached to the charpy striker for the signal collection. Aluminium 6061 and low carbon steel 1050 were used for extracting strain responses on the striker during the testing. In this work, the power spectrum density (PSD) approach was then used for the energy based observation and a signal was converted from the time domain to the frequency domain using the fast Fourier transform (FFT) method. Comparison between experimental findings with related parameters such as of different materials, strain signals pattern, I-kaz, were finally correlated and discussed. It was found that the modulus of elasticity were proportional to the energy absorbed, strain signals amplitude and PSD. Finally, it is suggested that the properties of materials and the impact signals pattern is suitable to be analysed using the signal processing approach.

Abstract: Three sets of fatigue crack growth data tested under different constant-amplitude loads for CT specimens made of 2024 T-351 aluminum alloy are released, and the analyzed results presented in this study are specially emphasized on the correlation between statistics of these scattered fatigue data and their applied loads. Investigating the scatters of initiation cycle and specimen life, it was found that both the mean and standard deviation of initiation cycle, as well as the mean and standard deviation of specimen life, decrease as applied stress amplitude increases. Moreover, the negatively linear correlation between the median values of initiation cycle and applied stress amplitudes presented in linear scale, and between the median values of specimen life and applied stress amplitudes presented in logarithmic scale were found, where the initiation cycle and specimen life are all best depicted by normal distributions for all three data sets. Finally, the mean of intercepts and mean of exponents of Paris-Erdogan law for each data set were studied, and it was found that the mean of intercepts decreases greatly as applied stress amplitude increases, while the mean of exponents decreases slightly.

Abstract: Fatigue damage assessment is very important in design process of the component to determine their durability under service loading conditions. In service, the great majority of structures and components are subjected to stress of variable amplitude loading. The purpose of this research is to analyse statistically of two types of strain signals from road loading and compare their effect on fatigue damage of the engine mount bracket. Strain gauges were attached to the engine mount bracket and were connected to the data acquisition set in order to capture the actual strain signals when an automobile was driven on two different road surfaces. The strain signals were then analysed using global signal statistic and integrated kurtosis based algorithm for Z-filter (I-kaz) method. Meanwhile, damage of the engine mount bracket was evaluated using finite element commercial software. From the analysis, it was found that the fatigue damage showed an increment with the respective statistical values of the strain signals.

Abstract: The fuzzy comprehensive evaluation method is used to compare the heat and moisture comfort performance among the natural bamboo fabric, silk and pure cotton fabric, which is helpful in studying the summer clothing and further developing and designing the product