Analysis Of Crack Propagation In Structures Research Articles

Fatigue crack propagation analysis in structures with random parameters based on polynomial chaos expansion method

Fatigue fracture is the most common failure for aircraft structures, therefore fatigue life prediction plays an important role in structure design. However, uncertainties widely existing in engineering structures make it difficult to analyze crack propagation and predict fatigue life. This paper presents a novel efficient and accurate approach to crack propagation analysis in structures with random uncertainties based on polynomial chaos expansion (PCE) method. For short fatigue crack in aircraft skin or armor plate of tank, the structure can be regarded as an infinite plate. In this situation, the stress intensity factor range has a simple analytical expression and a basic crack propagation equation is derived based on it. Considering uncertain parameters, crack length is regarded as a random variable and expanded into orthogonal polynomial series after introducing Hermite polynomials. Because crack length is a time-dependent variable, the coefficients in polynomial series are regarded to be time-dependent. In order to determine values of these coefficients, orthogonal polynomial series of crack length is substituted into Paris law and a series equations are obtained considering the orthogonality of Hermite polynomials. Time history of the coefficients is acquired by solving these equations using numerical algorithm. Furthermore, expectation and standard deviation of crack length can be easily obtained. The proposed method is verified based on three numerical examples and Monte-Carlo Simulation (MCS) is applied for the sake of validation. The results demonstrated the accuracy and efficiency of the proposed method for crack propagation analysis of structures with random parameters.

Crack propagation in structures with uncertain-but-bounded parameters via interval perturbation method

Fatigue crack growth prediction plays a crucial role in structure design. This paper presents a method for crack propagation analysis in structures with uncertain-but-bounded parameters. Although the parameters of engineering structures are uncertain due to many factors, the range across which they vary can be determined from practical experience and engineering knowledge. The crack growth boundary over the life of the structure has great significance in preventing structural failure. Uncertain-but-bounded parameters are regarded as interval numbers in the proposed method, and expressed alongside time-varying crack length under Paris law as a perturbation series after introducing a small parameter. By combining the perturbation method with interval mathematics, boundaries of each term in the perturbation series of time-varying crack length are determined to obtain the upper and lower boundaries of time-varying crack length. The proposed method is verified based on two examples; both the Monte-Carlo method and probabilistic method are applied for the sake of validation. The results demonstrate the feasibility and efficiency of the proposed method for predicting crack propagation in structures with uncertain-but-bounded parameters.

Three-dimensional fracture and fatigue crack propagation analysis in structures with multiple cracks

A methodology is presented for fracture and fatigue crack growth simulations of multiple cracks. Computed stress intensity factors and a crack growth law are used to predict incremented positions of crack front nodes. The procedure is repeated until failure criterion is reached. The cases presented in this study include structures containing two or more cracks which propagate, coalesce or grow as planar and non-planar cracks. Comparisons of results with literature data shows excellent agreement. Therefore, it is concluded that the presented procedure can be used to accurately to assess fatigue crack propagation behavior of structures with multiple three-dimensional cracks.