Experimental Investigation Of Fatigue Behavior Research Articles

Fatigue behavior of pultruded fiberglass tubes under tension, compression and torsion

This work is devoted to an experimental investigation of fatigue behavior of pultruded fiberglass tubes under uniaxial tension, compression and torsion. Static tests were carried out; a presence of postcritical deformation stage during torsion is noted. Regularities of inhomogeneous strain fields evolution are analyzed using digital image correlation method. Fatigue curves are built for four cyclic loading modes: tension-tension, compression-compression, tension-compression and torsion. An analysis of specimens' fractures is carried out, typical damaging mechanisms are revealed. Residual dynamic stiffness data is obtained and studied using a previously proposed fitting model. Results demonstrate model's high descriptive capability and its flexibility to describe two-staged and three-staged stiffness degradation curves. An influence of loading mode on a shape of these curves is found out. Model parameters' dependence on maximum stress value during the loading cycle is studied using the Pearson's correlation coefficient. The necessity of multiaxial fatigue behavior investigation of pultruded fiberglass tubes is concluded.

Experimental investigation of fatigue behavior of UHPFRC – RC composite deck slabs subjected to moving wheel loading

UHPFRC has been increasingly used as a bridge deck overlay material. Since bridge decks are exposed to severe mechanical action and harsh environmental conditions, the application of UHPFRC to bridge decks is an effective and wise utilization of UHPFRC’s excellent properties such as high strength and low permeability. This paper presents the result of a full-scale fatigue test of a reinforced concrete (RC) deck slab overlaid with UHPFRC (UHPFRC – RC composite deck slab) using a moving wheel load. The fatigue behavior of the UHPFRC – RC composite deck slab was analyzed using measurement data from the experimental test and discussed. The failure mode of the UHPFRC – RC composite deck slab was punching shear accompanied by near-interface concrete cracking and double curvature bending of the UHPFRC layer. The fatigue life of the UHPFRC – RC composite deck slab was estimated using an existing S-N relation of RC deck slabs subjected to moving wheel loads and a 30 mm thick UHPFRC overlay was found to increase the fatigue life of RC deck slabs by about five times.

Experimental investigation of fatigue behavior for adhesively-bonded GFRP/steel joints

The fatigue behavior of an adhesively bonded glass fiber-reinforced polymer (GFRP)/steel double-lap joint (DLJ) under cyclic tensile loading with load ratio R = 0.1 was experimentally studied. Results in terms of failure mode, F-N curve, stiffness degradation law, crack initiation and propagation laws were obtained. Linear and nonlinear models of stiffness degradation and a mathematical model of the crack growth rate were developed for the adhesive GFRP/steel DLJ under fatigue loading. The fatigue performance of adhesive GFRP/steel DLJ was compared with that of adhesive GFRP/GFRP DLJ to identify the differences between these behaviors. The results demonstrated that the stiffness degradation law of the adhesive GFRP/steel DLJ can be objectively and accurately characterized by the nonlinear stiffness degradation model in terms of the equivalent shear stiffness. The crack initiation life and the ratio between the crack initiation life and fatigue life increased with the deceasing maximum applied load. The fatigue life of the GFRP/steel DLJ was more sensitive to the variation in the maximum applied load compared with that of the GFRP/GFRP DLJ. Moreover, the decaying rate of stiffness and the interfacial crack propagation rate for the GFRP/steel DLJ under fatigue loading were larger than those for the GFRP/GFRP DLJ.

Fatigue behavior of steel reinforced concrete (SRC) beams with different shear span-to-depth ratios

There is an increase in the use of steel reinforced concrete (SRC) beams in high-speed railway platforms and bridges that are subjected to fatigue loading. It was found by the authors in their previous research on SRC beams under fatigue loading that flexural fatigue failure was the dominating failure mode when a large shear span-to-beam depth ratio (λ) of 2.63 was used. Research on reinforced concrete (RC) beams under fatigue loading and research on SRC beams under static loading revealed that shear failure may dominate when the shear span-to-beam depth ratio gets smaller. It is unknown if shear fatigue failure will happen in SRC beams with smaller shear span-to-beam depth ratio. This paper presents an experimental investigation of fatigue behavior of SRC beams with shear span-to-beam depth ratio of 1.8, 1.5, 1.1 and 1.0. It was found that shear fatigue failure did not occur in all twenty-seven SRC beams tested even for λ ratio as low as 1.0. Because the failure mode is found to be the same (i.e. dominated by flexural fatigue failure) for all the SRC beams with λ ranging from 1.0 to 2.63, the test results of all 39 SRC beams under fatigue loading were grouped together to derive fatigue strength curves for SRC beam design.

An experimental investigation of fatigue behavior and deformation of double spot friction welded joints

Fatigue behavior of double spot friction welded joints in aluminum alloy 7075-T6 plates is investigated by conducting monotonic tensile and fatigue tests. The spot friction welding procedures are carried out by a milling machine with a designed fixture at the best preliminary welding parameter set. The fatigue tests are performed in a constant amplitude load control servo-hydraulic fatigue testing machine with a load ratio of (R=Pmin/Pmax) 0.1 at room temperature. It is observed that the failure mode in cyclic loading (low-cycle and high-cycle) resembles that of the quasi-static loading conditions i.e. pure shearing. Primary fatigue crack is initiated in the vicinity of the original notch tip and then propagated along the circumference of the weld’s nugget.

Experimental investigation of fatigue behavior of spur gear in altered tooth-sum gearing

This paper deals with the contact stress, power loss, and pitting of spur gear tooth in altered tooth-sum gearing for a tooth-sum of 100 teeth when altered by ±4% tooth-sum. Analytical and experimental methods were performed to investigate and compare the altered tooth-sum gearing against the standard tooth-sum gearing. The experiments were performed using a power recirculating type test rig. The tooth loads for the experimental investigations were determined considering the surface durability of gears. A clear picture of the surface damage was obtained using a scanning electron microphotograph. The negative alteration in the tooth-sum performed better than the positive alteration in a tooth-sum operating between specified center distances.

Experimental investigation of fatigue behaviour for welded joint with mechanical heterogeneity : Cheng, G., Kuang, Z.B., Lou, Z.W. and Li, H. Int. J. Pressure Vessels Piping (1996) 67 (3), 229–242

High-cycle and low-cycle fatigue properties of aluminum alloy A5083 base and A5183 weld metals and the effect of welding structure on their fatigue properties have been investigated at cryogenic temperatures in order to evaluate the long-life reliability and safety of the structural materials used in liquid hydrogen supertankers and storage tanks and to develop a welding process for these applications. In the high-cycle fatigue tests, the S–N curves of A5083 base and A5183 weld metals shifted to higher stress levels, i.e., the longer life side at lower test temperatures. The ratios of 106-cycles fatigue strength (FS) to tensile strength (TS) for A5183 weld metals were slightly lower than those of A5083 base metals at each test temperature. Although the ratios of FS to TS for austenitic stainless steels weld metals at 4 K decreased substantially to about 0.4, that of A5183 weld metal was 0.65 even at 4 K and it indicated an excellent high-cycle fatigue property. Fatigue crack initiation sites in A5183 weld metals were occurred from the blowholes if the blowholes were located in the vicinity of the specimen surfaces. However, effects of the blowholes on high-cycle fatigue properties are not clear or significant. In the low-cycle fatigue tests, the fatigue lives of A5183 weld metals were slightly shorter than those of A5083 base metals at cryogenic temperatures. However, the fatigue lives of A5183 weld metals at 4 K were superior to that of conventional A5083 weld metals. The deterioration of low-cycle fatigue properties of A5183 weld metals at cryogenic temperatures were due to the intergranular fracture surface observed in fatigue crack propagation regions.

Experimental investigation of fatigue behaviour for welded joint with mechanical heterogeneity

Because of material and mechanical heterogeneity in welded joints, experimental studies of low-cycle fatigue (LCF) life and fatigue crack initiation behaviour were performed on weld metal, heat-affected zone (HAZ) and base metal of 16 MnR pressure vessel steel. A fatigue damage test was carried out by introducing a new damage variable. The fatigue damage evolution laws in each zone of a welded joint were obtained. A circular-notched compact tension specimen was designed and the whole process of fatigue damage, crack initiation and crack growth in each zone was investigated. The effect of mechanical heterogeneity in welded joints on the fatigue damage behaviour and fatigue crack initiation life was also investigated. The experimental and theoretical results indicate that the fatigue behaviour is markedly different in three zones of welded joints; there is a trend toward reduction in the fatigue life of HAZ as compared with the base metal. The weld metal does not have the same fatigue behaviour as confirmed by LCF life and crack growth rate. This study leads to the conclusion that fairly accurate estimates of fatigue life for welded joints should include the whole process of fatigue damage evolution and fatigue crack initiation as well as crack growth. Furthermore, a local experimental method should be carried out for weld metal, HAZ and base metal, respectively. Finally, the local fatigue failure criterion based on the weakest chain model has been presented.