복합하중을 받는 철강재 노치부재의 고사이클 피로강도 평가기법에 관한 연구

Abstract

기계부품이나 구조물부재의 파손은 전체 시스템운용에 큰 영향을 미칠 수 있으며 대부분의 원인이 피로파괴에 기인한 것으로 알려지고 있다. 따라서 이러한 부재들의 설계과정에서 피로강도의 평가가 필수적으로 요구된다. 일반적으로 이러한 부재들은 기능상 여러가지 형태의 노치를 포함하게 되고 노치 부근의 응력집중으로 인하여 피로강도의 저하를 가져오게 된다. 그러므로 이러한 노치국부 형상에 따라 피로강도 특성이 달라지게 되고 따라서 설계과정에서 이러한 부재들에 대해 일일이 시험을 통하여 피로강도를 평가한다는 것은 많은 시간과 비용이 소요되는 일이다.

본 연구는 구조물용 철강 및 탄소강 재료의 여러 형태의 노치재에 대하여 참고문헌에서 제시된 고사이클 피로?쳬? 결과를 분석하여 얻은 상대응력변화율과 노치부의 피로강도 사이의 상관관계를 바탕으로 노치재의 장수명 피로강도를 추정하는 평가기법을 제시하였다. 또한 기계부품이나 구조물 부재에 작용하는 피로하중은 일반적으로 복합적인 하중형태가 많으며 이러한 복합하중 하에서의 피로강도를 등가응력 형태로 고찰하였다.

In the design of machines and structural components, which are made of various steels, cyclic loading and resulting fatigue damage necessitate estimates of fatigue strength for a designed service life to ensure safety and durability. Moreover, it is inevitable to involve notch-like geometric shapes on the components, and also to be situated under combined loading conditions in real structures. Therefore it is often a difficult task to evaluate allowable strength to resist fatigue problems. And if component tests should be performed to verify fatigue design for every fatigue critical items, it will be absolutely tedious and ineffective during design work.

In this reason, a simple and effective procedure is required to evaluate fatigue strength for given shapes and dimensions. Assessments of allowable fatigue strength in these problems, are based on the variation and distribution of stresses near the notch root at most critical location. A number of studies have shown that fatigue damage on local notch root does not directly depend on the maximum local stress, but rather on the relative stress gradient at near notch root.

This paper shows how the stress gradient is related to the allowable fatigue strength for notched members under combined loading conditions, using various test data which have been published on several references.

In the design of machines and structural components, which are made of various steels, cyclic loading and resulting fatigue damage necessitate estimates of fatigue strength for a designed service life to ensure safety and durability. Moreover, it is inevitable to involve notch-like geometric shapes on the components, and also to be situated under combined loading conditions in real structures. Therefore it is often a difficult task to evaluate allowable strength to resist fatigue problems. And if component tests should be performed to verify fatigue design for every fatigue critical items, it will be absolutely tedious and ineffective during design work.

In this reason, a simple and effective procedure is required to evaluate fatigue strength for given shapes and dimensions. Assessments of allowable fatigue strength in these problems, are based on the variation and distribution of stresses near the notch root at most critical location. A number of studies have shown that fatigue damage on local notch root does not directly depend on the maximum local stress, but rather on the relative stress gradient at near notch root.

This paper shows how the stress gradient is related to the allowable fatigue strength for notched members under combined loading conditions, using various test data which have been published on several references.