Design Life Prediction Research Articles

Stochastic Evaluation of Structural Steel Plates Corrosion in Offshore Platforms

This study presents the structural reliability of steel plates on offshore platforms exposed to corrosion during their design period and beyond. The reliability-based design of steel plates exposed to corrosion was carried out with First Order Reliability Method coded in a computer based program, (FORM 5) and a Finite element method in a software (ABAQUS). The rate of corrosion of the steel plates was determined using a standard expression for extreme marine environment. From the results obtained using FORM 5, the safety indices ranged from 1.18 to 11.0, and a non-linear relationship exist between safety indices and thickness for different parameter variations. However, it was also noted that the design formulation is robust enough to exceed the design life prediction in the code by about 20% of the current prediction.

Traction Inverter Highly Accelerated Life Testing With High-Temperature Stress

Highly accelerated life testing (HALT) is one of the most popular step-stress testing methodologies for identifying the weaknesses and increasing product reliability in a fast and cost-efficient way. The traction inverter plays a critical role in EV/HEV power train systems, and the requirements on its reliability at the harsh environment operation are becoming more demanding. In this article, to evaluate the weak links and various components performance and ascertain the effect of high temperature on the traction inverter, the traction inverter HALT was carried out with high-temperature stress between 190 °C–220 °C taking the IGBT on-die temperature as the benchmark. Nine traction inverters were tested, which were divided into four groups with respect to the designed step-stress test profile. The changes in electrical and thermal indicators were observed online using the proposed monitoring system. At the end of each test, the effects of different conditions on the overall testing time, failure modes, and damage were examined, and the damages were listed systematically and discussed. Furthermore, the characteristics of the dc-link capacitor at different temperatures and the related degradation were observed online. The results show that the inverter can operate hundreds of hours with the IGBT on-die temperature of 200 °C, and the gate driver board chip of 127 °C. The findings in this study could help to the improvement design of the traction inverter, as well as to keep the design life prediction never be overestimated.

자연 노화된 폭발볼트의 성능 평가에 관한 연구

폭발볼트는 각종 유도무기 및 우주발사체에서 결합 및 분리기능을 수행한다. 이처럼 유도무기 체계에서 폭발볼트의 역할은 매우 중요하며, 임무 실패시 체계 전체 실패의 원인이 될 수 있다. 이와 같은 이유로 폭발볼트의 설계 수명 예측에 대한 요구가 최근에 지속적으로 발생하였지만, 신뢰도 높은 예측방법이 제시되지 못하고 있다. 기존의 가속노화 방법을 적용하기 위해선 폭발볼트의 활성화 에너지와 가속계수를 알고 있어야 한다. 현재 가속노화에 필요한 정보를 정확히 확보하지 못한 상황에서 폭발볼트의 설계 수명을 예측하는 것은 어렵기 때문에 본 연구에서는 실제 10년 이상 자연 노화된 폭발볼트를 이용해 성능을 평가하고, 이를 바탕으로 최소한의 설계 수명을 제시하였다. Explosive bolt is coupled in a variety of guided weapons and space projectiles, to perform the separation function. Thus, the role of the explosive bolt in guided weapons systems is very important, as it can cause failure of the entire system in the case of mission failure. For this reason, the design life prediction for explosive bolt is highly and frequently required recently, but its accurate prediction method has not been presented. In order to apply the existing accelerated aging process, we should know the activation energy and the acceleration factor of the explosive bolt. Since the information required for accelerated aging is not presently secured, it is difficult to predict the design life of explosive. Thus, in the present study, we have evaluated the performance of actual explosive bolts in the condition of natural aging over 10 years in order to present a minimum design life.

Design Life Prediction of Structural Components Subjected to Various Fatigue Loadings

Abstract Many structural components are subjected to cyclic loading, fracture being the most common form of failure. Design life assessment and reliability prediction of engineering components for in-service conditions, with the external loads of irregular and random nature, are obviously critical issues. The present work is an investigation of fatigue crack growth rates and design life assessment of the structural components subjected to various types of fatigue loadings. The life prediction has been carried out by linear elastic fracture mechanics (LEFM) principles using commercial package MATLAB(R) and FORTRAN(R) programming language. Modified Wheeler Model (MWM) and Crack Closure Model (CCM) have been applied to evaluate fatigue crack growth and its retardation due to interaction between the materials and various overloads (single, multiple and spectrum). The MWM is based on plasticity induced effects in front and in the wake of an advancing crack and CCM is based on the crack closure effects. Studies on design life assessment of cracked plate panels and other structural members subjected to tensile-compressive overloading-underloading have been carried out for validating these models. Quantitative retardation based on the residual stresses with an effective stress intensity factor has been developed using MWM and applied to the material specimen: plates with center crack-350 WT Steel, 7075-T6 Al- Alloy and plate with edge crack for 6061-T6-Al-Alloy to predict the design life of components under various fatigue loadings. The results obtained have been compared with the experimental results. Various fatigue crack growth rate equations of constant amplitude loading models in conjunction with Wheeler Model have been incorporated in the design life estimation and compared with the experimental data and are in good agreement.

Design Life Prediction of a Heavy Haul Track Foundation

Transnet Freight Rail monitors the behaviour of a new track foundation, constructed in 2004, on the South African Coal Line. This site forms part of a major rehabilitation project, aimed at increasing the capacity of the line to sustain future growth in annual tonnage. Sophisticated instrumentation is used to measure resilient and permanent deformation of the track foundation. Preliminary results of this research were published shortly after the construction of the new track foundation. Results of the permanent deformation, gathered over a period of 5 years, are now presented to provide new insight into the long-term behaviour of track foundations. Permanent deformation measurements are used to calculate the expected design life of a track foundation. The results are used to predict permanent deformation and ultimately the design life of the track foundation under heavy haul loading conditions. The research provides a scientific basis for planning foundation rehabilitation in the light of sustained capital expansion and projected tonnage increase on the Coal Line and other heavy haul lines.

Modeling the Effects of Damage and Microstructural Evolution on the Creep Behavior of Engineering Alloys

A quantitative representation of the creep behavior of materials is required to determine the operating lives of high temperature plant. Although the creep performance of such materials is normally governed by the development of microstructural features that can either be associated with the normal aging phenomena or by the development of damage in the material, most previous analyses of creep data have been empirical. It has been implicitly assumed that similar forms of creep curves can be adequately represented by a single generic equation. However, it is clear that different materials are subject to different combinations of structural change during their creep lives (e.g., cavitation/cracking, particle coarsening, phase changes, dislocation accumulation) all of which can influence the creep performance. An empirical representation can always be made to fit an available database, but effective extrapolation to longer lives and more complex loading conditions requires that the differing mechanisms be integrated in the creep equations. This paper will explore the implications of the evolution of microstructure and damage on the creep performance of a range of materials and will consider the potential of a microstructure-based state-variable (or damage-mechanics) approach for improved design life prediction of new plant and remaining life assessment of geriatric plant. [S0094-4289(00)00603-4]

Effect of a proof test on the fatigue strength and lifetime of soda-lime glass

The effect of a proof test on the fatigue strength and lifetime of soda-lime glass specimens is studied. In practice, subcritical crack growth is difficult to avoid during the proof test so that the initial damage should be considered in the design life prediction process. Statistical treatment assumes that the fatigue lifetime depends on the Weibull modulus m, the material and environment dependent exponent n in the crack growth rate model and the eliminated ratio specimens in the proof test. The effect of the proof test becomes increasingly more important as this ratio is increased. For m/( n − 2) = 1, the statistical distribution of the fatigue strength is unchanged after the proof test. If m/( n − 2) becomes smaller than unity, the proof test raises the fatigue strength of the survived specimens, especially at higher survival probability, and reduces the scatter of the fatigue strength data. Hence, the reliability of the survival components is improved. The opposite occurs when m/( n − 2) becomes greater then unity.