Papers by Keyword: Fatigue Testing

Abstract: In this paper experiments on the fatigue behavior of flat and tubular Glass Fiber Reinforced Plastics (GFRP) specimens with three different layups ([0/90₅/0], [0/90₂/0_1/2]_s and [0/±45/0_1/2]_s) are presented. The experiments are conducted to study the mechanics under cyclic tension-tension loading (R=0.1) until crack saturation (CDS). Fatigue testing is performed below the critical static load level where first matrix cracks can be observed. Therefore Load Levels (LLs) are derived from crack evolution curves obtained by static tests under usage of transmitted light photography. The shear lag model of Berthelot [1] is applied to the two cross-ply specimens to predict crack evolution. The results show good agreement between the prediction and the experimental data. Deviations can be found in prediction of crack evolution in [0/90₂/0_1/2]_s-specimens. For predicting fatigue stiffness degradation the phenomenological model of Adden [2] is used. The results show good capabilities for predicting stiffness degradation after crack onset.

Abstract: Structural loading of cellular metals is strongly affected by brittle fracture of cell struts and walls that exhibit tensile loads, e.g., during fatigue loading. The present paper summarizes results of compression, tension and cyclic loading experiments on various closed-cell metal foams and metal foam sandwiches (Alulight, Alporas, Foamtech, AFS) using various mechanical testing systems. The results were correlated with a thorough analysis of the cellular mesostructure and the cell strut/wall microstructure by means of scanning electron microscopy revealing defects, such as casting porosity and large Si precipitates in the Al-Si eutectic of aluminum cast alloy. The results of the work served for the definition of testing standards for compression testing (ISO 13314) and tensile testing (DIN 50099), which are outlined in the paper. Such standards and design guidelines are crucial for a successful implementation of cellular metals in innovative products in mechanical, automotive and energy engineering as well as in bioengineering.

Abstract: Due to the deficiencies such as shallow hardened layer and short fatigue life of the ball screws treated by the traditional induction quenching process, a new process has been developed. The new induction quenching process has four-turn induction coil. The power of the this process is 150-160kw, feeding speed 270mm/min and the spraying cooling water distance is 35mm. It has been successfully used on the Cr-Mo steel ball screw with a diameter of 80 mm. The microstructure and hardness distribution of the induction hardened layers were investigated by a metallographic microscope and a micro-hardness apparatus. The fatigue life of the ball screw was measured through a constant stress accelerated fatigue test. The degree of fatigue wear on the raceway of the ball screw was analyzed by a field emission scanning electron microscopy (FE-SEM). The experimental results showed that the microstructure and hardness distribution of the hardened layer of the Cr-Mo steel ball screw could satisfy the design requirements of contact fatigue resistance. The fatigue life was longer than the theoretical service life and there was no obvious fatigue wear on the raceway after the fatigue testing. It shows that the safety and reliability of the Cr-Mo steel ball screw fabricated through the new induction quenching process could be guaranteed in practical application.

Abstract: The damage to the propeller shaft, a principal mechanical component in the power transmission system of Boats makes engines work harder than normal attributed to less transmission efficiency. Operating boats with the damaged propeller shaft increases the rate of fuel consumption per distance and cost of fishing which affects income of coastal fishermen. The result of a preliminary survey of Boats at Kaoseng Community revealed that the service life of the damaged propeller shafts caused by the fatigue failure would be repaired by shield metal arc welding process. The statistical analysis showed that the useful life depended on fatigue endurance limit of welding surface. When they were back to be used again. The objective of this research was to study the fatigue life of hardfacing surface by solid wire. The method of this research included (a) building up the hardfacing surface (b) forming specimen from hardfacing surface and (c) finding out the fatigue life by fatigue testing machine base on ASTM E739-91 standard. The results of this research indicated that hardfacing surface by solid wire could not receive fatigue stress exceed 500 MPa. The propeller shafts after being repaired will have very short service life, which is not feasible in engineering economy.

Abstract: LAU-7 missile launcher housings, which are fitted to most Royal Australian Air Force (RAAF) F/A-18A/B aircraft, can experience cracking in the guide rail. This paper covers the design, manufacture and validation of a life extension repair for cracked launcher housings. The repair development uses DSTO's rework shape optimisation technology and fatigue testing capabilities. The rework design reduces peak stresses by 33 %, resulting in significant fatigue life enhancements, as demonstrated by representative coupon testing. A special manufacturing jig has been designed and transitioned to the RAAF, which has used it to repair housings. These housings have performed well in flight tests, with no cracking detected.

Abstract: Aircraft full-scale fatigue tests are expensive to conduct and they are a critical item on the certification path of any aircraft design or modification. Two aspects that contribute to the cost of a test are its duration and the loads spectrum development process. This paper provides a summary of a proposed supplemental pseudo full-scale fatigue test (FSFT) aimed at rapid certification. In this instance the method was developed with the aid of extant FSFTs that were found to be deficient. The proposed process involves the development of proof loads, damage size estimates, a loads application rig, insertion of the target damage or modifications and conducting proof testing. As all locations with a propensity to crack are known, the process is considered to be the equivalent of having conducted a representative fatigue test for the required service life target and then demonstrating adequate residual strength (i.e. proof testing the damage state at the end of a FSFT).

Abstract: Zirconium dioxide is a material which over the recent years has been winning support among dental technicians and dentists. Due to its chemical composition and mechanical properties is can replace non-aesthetic caps or metal crowns. In their paper the authors have focused on the analysis of the material itself; zirconium dioxide under the trade name LAVA and assumed a single treatment technology developed together with dentists. The main objective of the study was to determine the S-N curve for the material that is zirconium dioxide. The next step for the authors was to perform a static three-point bending. Fatigue testing covered a group of 30 specimens which were then used to determine the S-N curve for zirconium dioxide. The authors determined the S-N curve thanks to which the dentists are able to predict the destruction of the construction element which presents all-ceramic substructure. In the lecture review and according to authors it is said that in the aqueous environment the values of stress are similar with the dry environment and are within 850 MPa.

Abstract: The paper deals with the effect of different shot peening (SP) treatment conditions on the ENAW 7075-T651 aluminium alloy. Suitable residual stress profile increases the applicability and life cycle of mechanical parts, treated by shot peening. The objective of the research was to establish the optimal parameters of the shot peening treatment of the aluminium alloy in different precipitation hardened states with regard to residual stress profiles in dynamic loading. Main deformations and main residual stresses were calculated on the basis of electrical resistance. The resulting residual stress profiles reveal that stresses throughout the thin surface layer of all shot peened specimens are of compressive nature. The differences can be observed in the depth of shot peening and the profile of compressive residual stresses. Under all treatment conditions, the obtained maximum value of compressive residual stress ranges between -200 MPa and -300 MPa at a depth between 250 μm and 300 μm. Comparison of different temperature-hardened aluminium alloys shows that changes in the Almen intensity values have greater effect than coverage in the depth and profile of compressive residual stresses. Positive stress ratio of R=0.1 was selected. Wöhler curves were determined in the areas of maximum bending loads between 30 - 65 % of material's tensile strength, measured at thinner cross-sections of individual specimens. The results of material fatigue testing differ from the level of shot peening on the surface layer.

Abstract: In order to reduce the time and labor cost, an unattended testing system which can be monitored remotely for fatigue crack growth threshold test was developed. Compliance technique is used to measure fatigue crack length automatically. GSM modem and industrial camera are utilized to realize remote monitoring. Fatigue crack growth threshold test on J2 steel, which is used on the wheel of high-power locomotive, has been carried out with the developed system. The testing process and results demonstrated the safety and efficiency of the system.

Abstract: Aluminum alloys generally contain constituent particles. The population density and size these particles are important while considering fatigue performance. In present study, the crack growth process in stage II in the rolled plate of a high strength aluminum alloy AA 2219 was studied on samples prepared along the rolling direction. A three fold approach was adopted to understand the fatigue crack growth process: i) microstructural analysis ii) fatigue testing iii) post-fracture analysis. Microstructural analysis revealed a high density of constituent particles in the material. EDS analysis showed that the particles were mainly of CuAl2 type. However, particles with high concentration of Fe and Mn were also present in the material. Fatigue crack propagation tests were performed by using middle tension (MT) specimens prepared in rolling direction under constant amplitude loads. The da/dN vs ΔK plot on log-log scale showed a sigmoidal shape with a sharp increase of crack growth rate in the steady state regime. Topographical features were studied to understand the interaction of fatigue crack with the microstructural features. Post fracture analysis revealed that the macro fracture appearance changed with the change of stress level. However, the general mechanism of crack growth, in all the stress levels studied, was by formation of striations. At lower stress levels almost flat region with striations is present upto the final fracture. The crack growth surface showed crystallographic features with crack propagation almost perpendicular to the loading direction. However, a comparatively tortuous fatigue region was evident in the sample tested at high level of stress. The observation of crack path surface at high magnification did not reveal any influence of particles on the crack growth process. However, in sections taken from the fractured samples cracking and debonding of the constituent particles was observed near the fatigue crack path.