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[en] Rock structures, in reality, may be subjected to reversed tension-compression loading conditions due to blasting, earthquake, and traffic or injection-recovery process. In this case, loading frequency may have a great influence on fatigue life and behavior of rocks. The effect of loading frequency on fatigue life of a crystalline rock sample under fully reversed loading condition was examined. A new apparatus, based on the R. R. Moore fatigue test machine, was used to assess the fully reversed loading condition. The experimental tests were conducted with five sets of loading frequency and five levels of stress based on the ultimate tensile strength of samples. The test results showed that the variation of ultimate fatigue stress versus loading cycle number (S-N curve) of crystalline rock samples were in accordance with the observed results in other materials such as metals and ceramics. The results showed that fatigue life of a component is positively correlated with the frequency level. The fatigue life improves with increasing the loading frequency, but the improvement was more tangible at lower stress levels than at higher stress levels. The effect of loading frequency in an ordinary S-N equation was also formulated. The results also showed that the loading frequency does not influence the fatigue limit.
ConclusionA technique for replicating diffraction grating on to compliant and porous materials has been developed. The grating can be applied quickly to the specimen. It is also highly compliant and localized on the specimen surface. Three applications described illustrate replication method provides high quality fringe patterns.
[en] In the production process of lithium-ion secondary batteries, the lap-joint quality of the safety vent and the cathode lead influences the product quality and production efficiency. A pulsed Nd:YAG laser welding machine was employed herein. The welding parameters that influence the pulsed Nd:YAG laser welding quality was evaluated by measuring the tensile-shear strength. In this study, the Taguchi method was used to perform the initial optimization of the process parameters. A neural network (NN) with the Levenberg–Marquardt back-propagation algorithm was adopted to develop the nonlinear relationship between factors and the response. Then, a genetic algorithm based on a well-trained NN model was applied to determine the optimal factor settings. Experimental results illustrated the proposed approach.
[en] The main difficulty when joining magnesium (Mg) and aluminum (Al) alloys by fusion welding process lies in the existence of oxide films and formation of brittle intermetallic in the weld region. However, solid-state welding processes such as friction welding and diffusion bonding are suitable processes to join these two materials. The diffusion bonding process parameters such as bonding temperature, bonding pressure, holding time, and surface roughness of the bond specimen play a major role to determine the joint strength. In this investigation, an attempt was made to develop empirical relationships to predict the lap shear strength and bonding strength of diffusion bonded dissimilar joints of AZ61A magnesium and AA6061 aluminum alloys, incorporating the above-mentioned parameters. Response surface methodology (RSM) was applied to optimize the diffusion bonding process parameters to attain the maximum shear strength and bonding strength of the joint. From this investigation, it is found that the bonds fabricated with the bonding temperature of 420.43°C, bonding pressure of 7.70 MPa, holding time of 27.15 min, and surface roughness of 0.10 μm exhibited maximum shear strength and bonding strength of 51.24 and 72.10 MPa, respectively.
[en] In this paper an improved sub-component fatigue testing method is proposed, in which structural optimization is used to obtain specimens in which fatigue failure is precipitated in the designated area away from the boundaries, i.e., load application and fixture points. This is achieved by optimizing the nonlinear beam taper and the dynamic excitation. The major requirement for accurate material characterization through sub-component tests concerns unbiased stress states in the gauge section. However, empiricism shows that many sub-component high-cycle fatigue testing methods suffer from failure in the boundaries rather than the gauge section, which causes bias. The common practice for reinforcing those regions only shifts the issue into new areas of local discontinuities where failure is still caused remotely from the gauge section. An experimental proof of concept demonstrates that optimization of the beam taper can be used to obtain unbiased fatigue test data.
ConclusionIn this paper, the performances of conventional incandescent and discharge lamps in photoelasticity are compared with LED devices. LED devices are found to have superior luminous efficacy, lamp life and flash response. Although the spectral bandwith of LEDs is broader than that of sodium discharge lamps, they are within the 100 nm limit necessary to ensure measurement accuracy. LED devices are also easily available in a range of wavelengths that enhance their application in photoelasticity when birefringent materials with selective spectral absorption characteristics have to be illuminated. With the availability of LEDs that radiate at different wavelengths, selection can be easily done by simple electrical switching. Due to their miniature construction, LED devices can also be designed as flat panel illuminators by connecting them up on printed circuit boards. Due to their versatility and improved characteristics, it is easy to conclude that LED devices are ideal for use as illuminators in photoelasticity. For a lens polariscope, a single LED provides adequate illumination and eliminates the problem with a multiple source image at the recording plane. It has been shown that a single LED provides adequate illumination even at exposure times of 1 µs. This has been used to develop a low cost Cranz-Schardin system.
ConclusionPreliminary results indicate that an optimized edge insert design can be achieved that provides good performance characteristics and can be cost effective to manufacture. The introduction of a higher modulus insert significantly reduces the core compression caused by the lower support rollers. Stress concentration locations can be altered through insert geometry and material changes.