Jun Tang

Structural durability design optimisation and its reliability assessment

Mechanical fatigue subject to external and inertia transient loads in the service life of mechanical systems often leads to structural failure due to accumulated damage. A structural durability analysis that predicts the fatigue life of mechanical components subject to dynamic stresses and strains is a computer-intensive, multidisciplinary simulation process, since it requires the integration of several computer-aided engineering tools and large amounts of data communication and computation. Uncertainties in geometric dimensions result in the indeterministic fatigue life of a mechanical component. Uncertainty propagation to structural fatigue under transient dynamic loading is not only numerically complicated but also extremely expensive. It is, therefore, a challenge to develop a durability-based design-optimisation process and reliability analysis to ascertain whether the optimal design is reliable. The objective of this paper is to develop an integrated CAD-based computer-aided engineering process to effectively carry out design optimisation for structural durability, yielding a manufacturable, durable, and cost-effective product. In addition, a reliability analysis is executed to assess the reliability of the deterministic optimal design.

An Efficient Methodology for Fatigue Reliability Analysis for Mechanical Components

This paper presents an efficient methodology to solve a fatigue reliability problem. The fatigue failure mechanism and its reliability assessment must be treated as a rate process since, in general, the capacity of the component and material itself changes irreversibly with time. However, when fatigue life is predicted using the S-N curve and a damage summation scheme, the time dependent stress can be represented as several time-independent stress levels using the cycle counting approach. Since, in each counted stress cycle, the stress amplitude is constant, it becomes a random variable problem. The purpose of this study is to develop a methodology and algorithm to solve this converted random variable problem by combining the accumulated damage analysis with the first-order reliability analysis (FORM) to evaluate fatigue reliability. This task was tackled by determining a reliability factor using an inverse reliability analysis. The theoretical background and algorithm for the proposed approach to reliability analysis will be introduced based on fatigue failure modes of mechanical components. This paper will draw on an exploration of the ability to predict spectral fatigue life and to assess the corresponding reliability under a given dynamic environment. Next, the process for carrying out this integrated method of analysis will be explained. Use of the proposed methodology will allow for the prediction of mechanical component fatigue reliability according to different mission requirements.

Application of Reliability-Based Design Optimization to Durability of Military Vehicles

In the Army mechanical fatigue subject to external and inertia transient loads in the service life of mechanical systems often leads to a structural failure due to accumulated damage. Structural durability analysis that predicts the fatigue life of mechanical components subject to dynamic stresses and strains is a compute intensive multidisciplinary simulation process, since it requires the integration of several computer-aided engineering tools and considerable data communication and computation. Uncertainties in geometric dimensions due to manufacturing tolerances cause the indeterministic nature of the fatigue life of a mechanical component. Due to the fact that uncertainty propagation to structural fatigue under transient dynamic loading is not only numerically complicated but also extremely computationally expensive, it is a challenging task to develop a structural durability-based design optimization process and reliability analysis to ascertain whether the optimal design is reliable. The objective of this paper is the demonstration of an integrated CAD-based computer-aided engineering process to effectively carry out design optimization for structural durability, yielding a durable and cost-effectively manufacturable product. This paper shows preliminary results of reliability-based durability design optimization for the Army Stryker AArm.

Large Scale Tracked Vehicle Concurrent Engineering Environment

In this paper, a fully integrated Tracked Vehicle Concurrent Engineering environment that exploits CAD and CAE technologies in support of simulation-based design of large scale tracked vehicles is presented. The Tracked Vehicle Concurrent Engineering environment comprises a series of engineering workspaces that include CAD/CAE Services, Tracked Vehicle Workspace, Dynamic Stress and Life Prediction Workspace, and Design Sensitivity Analysis and Optimization Workspace. These engineering workspaces are the principal functional components of the integrated simulation-based design environment that utilizes mechanical system data modeling techniques and ROSE object-oriented database to facilitate and manage data sharing. Wrappers have been developed to integrate these engineering workspaces by providing bi-directional data access and translation capabilities between the engineering workspaces and the database. In addition to these engineering workspaces, the Iowa Driving Simulator is integrated into the environment to provide a customer-driven simulation and design environment.

Structural Durability Design Optimization and Its Reliability Assessment

Mechanical fatigue subject to external and inertia transient loads in the service life of mechanical systems often leads a structural failure due to accumulated damage. Structural durability analysis that predicts the fatigue life of mechanical components subject to dynamic stresses and strains is a compute intensive multidisciplinary simulation process, since it requires an integration of several computer-aided engineering tools and large amount of data communication and computation. Uncertainties in geometric dimensions due to manufacturing tolerances cause the indeterministic nature of fatigue life of the mechanical component. Due to the fact that uncertainty propagation to structural fatigue under transient dynamic loading is not only numerically complicate but also extremely expensive, it is a challenging task to develop structural durability-based design optimization process and reliability analysis to ascertain whether the optimal design is reliable. The objective of this paper is development of an integrated CAD-based computer-aided engineering process to effectively carry out the design optimization for a structural durability, yielding a durable and cost-effectively manufacturable product. In addition, a reliability analysis is executed to assess the reliability for the deterministic optimal design.Copyright

Fatigue Reliability Based Optimal Replacement Decision Based on First Order Reliability Method

This paper introduces a maintenance decision-making strategy in the general area of the replacement and reliability of mechanical components. The decision-making strategy involves the optimization of the replacement interval based on fatigue failure of mechanical components. Fatigue reliabilities of a component under random cyclic loading need to be evaluated to determine the optimal replacement intervals under fatigue failure. This task is undertaken by determining a reliability factor using an inverse reliability analysis. A reliability-defined e-N curve (R-e-Nf curve) can be generated for an empirical e-N relationship and a “unique” reliability factor by modifying the nominal e-Nf curve using reliability factors for an assigned reliability. A family of R-e-Nf curves, which includes the conventional e-Nf curve, can then be obtained. Hence, fatigue life under specified reliability or reliability based on mission life can be predicted using these curves. This method can efficiently determine replacement intervals for components whose operating costs increase with use and replacement intervals for components subject to failure induced by random process. An example is presented to demonstrate the application of the present method.Copyright

Optimum Replacement Interval for Mechanical Components Based on Fatigue Reliability

This paper introduces a maintenance decision-making strategy in the general area of replacement and reliability of mechanical components. The decision-making strategy involves the optimization of replacement interval calculated from fatigue failure of mechanical components. The proposed approach is based on the cumulative damage distribution function for evaluating mean fatigue life. Using this approach, the analytical expressions for mean and variance of the cumulative damage distribution under both stationary narrow-band and stationary wide-band random process are provided. The mean value and variance of fatigue life distribution are then evaluated to determine the optimal replacement intervals under fatigue failure. A practical example is presented to demonstrate the application of the present method.

Application of a Reliability Method to Maintenance Strategy for Mechanical Components

This paper presents a maintenance decision-making strategy in the general area of replacement and reliability of mechanical components. The decision-making strategy involves the optimization of replacement interval based on fatigue failure of mechanical components. This new approach is based on the cumulative damage distribution function for evaluating mean fatigue life. By using the approach, the analytical expressions for the mean and the variance of the cumulative damage distribution under both stationary narrow-band and stationary wide-band random process are provided. The mean value and variance of the fatigue life distribution are thus evaluated to determine the optimal replacement intervals under fatigue failure. To evaluate probability function and the expected length of a failure cycle, approximated function forms were used.Copyright

Fatigue Reliability Based Optimal Replacement Decision of Mechanical Components

This paper introduces a maintenance decision-making strategy in the general area of replacement and reliability of mechanical components. The decision-making strategy involves the optimization of replacement interval based on fatigue failure of mechanical components. This new approach is based on the cumulative damage distribution function for evaluating mean fatigue life. By using the approach, the analytical expressions for the mean and the variance of the cumulative damage distribution under both stationary narrow-band and stationary wide-band random process are provided. The mean value and variance of the fatigue life distribution are thus evaluated to determine the optimal replacement intervals under fatigue failure. An algorithm of evaluating the mean and standard deviation of fatigue life is also presented. Therefore, the reliability of a component under random cyclic loading for a specified duration is quantified accordingly. Even though the new method introduces a great deal of complexity in the analytical models, this method can efficiently determine replacement intervals for component whose operating costs increases with use and replacement intervals for component subject to failure induced by the random process. An example is presented to demonstrate the application of the present method.Copyright

An Efficient Methodology for Fatigue Reliability Analysis of Mechanical Components Based on the Stress-Life Prediction Approach

An efficient methodology for fatigue reliability assessment and its corresponding fatigue life prediction of mechanical components using the First-Order Reliability Method (FORM) is developed in this paper. Using the proposed method, a family of reliability defined S-N curves, called R-S-N curves, can be constructed. In exploring the ability to predict spectral fatigue life and assessing the corresponding reliability under a specified dynamics environment, the theoretical background and the algorithm of a simple approach for reliability analysis will first be introduced based on fatigue failure modes of mechanical components. It will then be explained how this integrated method will carry out the spectral fatigue damage and failure reliability analysis. By using this proposed methodology, mechanical component fatigue reliability can be predicted according to different mission requirements.Copyright