Authors: Won Beom Kim, Jeom Kee Paik
Abstract: In this research, corrosion fatigue tests using 490MPa TMCP steel were performed in
synthetic seawater condition to investigate the corrosion fatigue crack propagation characteristics of
TMCP steel plate which is often used for ships and offshore structures from its weldability and weight
reduction purpose. In addition, relationships between boundary correlation factor F(α,β) and α(=
2a/W) of the fracture mechanics formula for the test specimen which was exerted by the pin load were
calculated for the evaluation of da/dN-.K. To get the boundary correlation factor F(α,β), the
calculation of J as a path-independent line integral was carried out. The solutions of J integral showed
similar value in spite of the different path. Crack propagation tests for the same steel in air condition
was carried out also for comparison. Finally, it was clear from the crack propagation test results that
the propagation rate of TMCP steel plate in synthetic seawater condition is faster than that of in air
condition at least twice.
1043
Authors: Won Beom Kim, Jeom Kee Paik
Abstract: In this research, corrosion fatigue tests using tensile strength of 490MPa TMCP steel
were performed in synthetic seawater condition to investigate the corrosion fatigue crack
propagation characteristics. The influence of cathodic protection at -800mV vs. SCE on the
corrosion fatigue crack propagation behavior was investigated. Relationships between da/dN versus
ΔK for the material were obtained by two types of test specimens. In the present study, F(α,β)
versus α(= 2a/W) relationship for the CCT specimen was calculated by J integral approach, while
that for the CT specimen was determined from ASTM E647. It is found that the fatigue crack
propagation rate of TMCP steel in synthetic seawater condition is faster than that in air condition at
least twice. Also, it is observed that the fatigue crack propagation rate of steel with cathodic
protection is in between those of seawater condition without cathodic protection and air condition.
1145
Authors: Jae Ung Cho, Li Yang Xie, Chong Du Cho, Sang Kyo Lee
Abstract: The objective of this study is to investigate the effect of the low or high strain rate on the impact fatigue properties of the nickel foam material and to understand the lifetime of this material which is subjected to the repeated impacts at different energy levels. Failures of foam materials under single and repeated impacts analogous to fatigue are essential to designers and users in military and aerospace structures. The material failure induced by repeated impact loading becomes a critical issue because of significant loss of stiffness and compressive strength in the foam material. Testing methods to study impact(that is, high strain rate) fatigue are quite numerous; no single standard testing procedure is defined for studying the impact fatigue property of a material. The increasing application of foam material in aerospace structures, owing to high specific stiffness and strength has attracted a great concern about the high sensitivity to impact damage introduced during manufacture or in service, and the effects of such damage on structural degradation. To investigate this issue, this study sets up an experimental procedure to determine the impact fatigue properties of nickel foam material. This study performs both experimental and numerical investigations to catch the impact fatigue behavior of nickel foam with open type. Design life and probability of failure or survival at specified life can be calculated so that the fatigue life of nickel core material subjected to repeated impact loading is predicted.
32
Abstract: Three cracked geometries loaded in mode I are investigated and the plastic zone size calculated. For estimation of the plastic zone size, two fracture criteria are used (Rankine and von Mises). Whereas the classical criteria give the same results (the stress intensity factor being identical for each geometry), the data from numerical simulations exhibit differences for various geometries. It is shown that the multi-parameter form of the criteria enables to obtain results that agree better to the numerical ones. Particularly, the Williams expansion is utilized for approximation of the stress components that serve as inputs for the fracture criteria. It is concluded that taking into account several more initial terms of the series can help to predict the plastic zone size more accurately.
169
Authors: Mathias Liewald, Fei Han, Ranko Radonjic
Abstract: Wrinkling is one of the primary failure modes in deep drawing of sheet metal parts. Previous studies showed that the second principle stress can be a measure for the initiation and growth of wrinkles. The wrinkling analysis is usually made with using conical cup geometries. Recent experiments and numerical simulation results at the Institute for Metal Forming Technology (IFU) showed that the wrinkling analysis using simple conical cup geometries is not suitable for description of complex wrinkling conditions for real deep drawing processes. In the presented experimental results, fender shaped geometry was chosen as an example. During deep drawing of this geometry, different wrinkling formulation mechanisms were observed. Regarding these wrinkling mechanisms, a new wrinkling limit curve can be determined. By use of this new wrinkling limit curve, it is possible to detect the occurrence of wrinkles in each area of the formed sheet metal part until the wrinkle is finally formed.
71
