Papers by Author: Philip Park

Abstract: Fatigue crack propagation behavior under cyclic tensile or torsional loading with biaxial static loads has been investigated. Two different biaxial loading systems, i.e. cyclic tensile loading with static torsional load and cyclic torsional loading with static tensile load, were employed to thin-walled tubular specimens. The crack propagation was measured by two crack gages mounted near the notch and crack opening level was measured by unloading compliance method. The directions of the fatigue crack propagated under respective biaxial loading conditions were examined and the growth rates were evaluated by using several cyclic parameters, including equivalent stress intensity factor range,
Keff, crack tip opening displacement range,
CTD, minimum strain energy density factor range,
Smin. Furthermore, the growth rates were evaluated by effective cyclic parameters considering crack closure. It was found that the biaxial static stress superimposed on the cyclic tensile or torsional loading tests has no influence on the propagation directions of the cracks. Furthermore, it was shown that the fatigue crack growth rates under biaixial faigue loading were well expressed by using the cyclic fatigue parameters,
Keq,eff,
CTDeff,
Smin,eff considering crack closure effect.

Abstract: Effects of crack on static behavior in steel box girder were investigated to identify the possibility of crack detection and location using conventionally measured static data including deflection and inclination. Finite element analysis with finely meshed 3-D models and experiments were performed for steel box girder with crack. To eliminate the variation according to load magnitude, compliance technique was applied to analysis of the result. Through this study, the quantitative relationship between crack size and structural responses of deflection and inclination were obtained as a form of relation-curve. This relation-curve can be utilized to evaluate crack size in the steel box girder bridge. The results also demonstrated that the location of crack can be estimated by static measurement.

Abstract: Fatigue crack initiation and propagation behavior around a hole subjected to various biaxial fatigue loading modes has been investigated considering the effect of the biaxial static stress. Two different biaxial loading systems, i.e. cyclic tensile loading with static torsional load and cyclic torsional loading with static tensile load, were employed to thin-walled tubular specimens with a circular notch. Variation of the initiaiton and propagation directions of the crack around a hole under these loading ssytems was examined. The initiation directions were observed using replication technique and the crack propagation was measured by two crack gages mounted near the notch. It was found that the biaxial static stress superimposed on the cyclic tensile or torsional loading tests has no influence on the initiation and propagation directions of the cracks around a hole. The fatigue crack initiation and propagation direction under cyclic loading with biaxial static load can be very well explained by the maximum of tangential stress range, Dsqq,max. Furthermore, it was shown that the fatigue crack growth rates under biaixial faigue loading becomes higher with increment of biaxial static load.

Abstract: This investigation aims at doing some durability and damage tolerant (DaDT) tests with 2124-T851 aluminum specimens having corner cracks under a random history, correlating with the simulation results from AFGROW and then drawing some conclusions from those comparisons. Two hydraulic actuators and a homemade Wood’s alloy grip are employed to do the test. The surface crack lengths are measured by a traveling microscope and used as a reference for the later fractography. The crack penetration and the total lives are about 17 and 27 blocks, respectively. The crack length and depth are evaluated by the fractography after completing each test and used to grasp the shape change. The Forman equation is used to simulate the fatigue crack growth behavior according to a bearing stress ratio extensively. The crack penetration life is decreased as the bearing stress ratio increases. The crack aspect ratio is very dependent on the bearing stress ratio. The LBH loading accelerates the fatigue crack growth in the crack depth direction but decelerates that in the length direction until crack penetration.