Search Results for prediction model

This article discusses corrosion fatigue, its effects on the damage tolerance of aircraft, and its predictive modeling. A conceptual framework is presented that incorporates two distinctive cyclic-based life-prediction philosophies and expands them both to include the time domain in order to consider the effects of corrosion. These philosophies include crack initiation used for safe-life design and crack growth used for damage tolerance. The article presents the methodology for computing the effects of real-time age degradation on an aircraft structure for two different corrosion types: crevice and pitting corrosion. It describes the rationale and techniques needed to apply the age-based structural integrity processes to in-service structures in order to realize the benefits throughout the full structural life cycle.

The systematic study of microstructural evolution during deformation under hot working conditions is important in controlling processing variables to achieve dimensional accuracy. This article explains the microstructural features that need to be modeled and provides an outline of the principles and achievements of each of the various microstructural models, including black-box modeling, gray-box modeling, white-box modeling, and hybrid modeling.

The microstructure that develops during the solidification stage of cast iron largely influences the subsequent solid-state transformations and mechanical properties of the cast components. This article provides a brief introduction of methods that can be used for simulating the solidification microstructure of cast iron. Analytical as well as numerical models describing solidification phenomena at both macroscopic and microscopic scales are presented. The article introduces macroscopic transport equations and presents analytical microscopic models for solidification. These models include the dendrite growth models and the cooperative eutectic growth models. The article provides some solutions using numerical models to simulate the kinetics of microstructure formation in cast iron. It concludes with a discussion on cellular automaton (CA) technique that can handle complex topology changes and reproduce most of the solidification microstructure features observed experimentally.

A computational tool would require the contribution of the strengthening mechanisms of metallic material to be predicted and then summed in an appropriate way to derive an estimate of the tensile properties. This article focuses on the modeling of deformation mechanisms pertinent to structural materials, namely, solid-solution strengthening, age/precipitation hardening, dispersion strengthening, grain size reduction, strengthening from cold work, and strengthening from interfaces. It explains the application of predictive models in the atomistic modeling of dislocation structures and cast aluminum property prediction. The article concludes with information on the use of rules-based approaches and data-mining techniques for quantitative predictions of tensile properties.

The lifetime assessment of polymeric products is complicated, and if the methodology utilized leads to inaccurate predictions, the mistakes could lead to financial loss as well as potential loss of life, depending on the service application of the product. This article provides information on the common aging mechanisms of polymeric materials and the common accelerated testing methods used to obtain relevant data that are used with the prediction models that enable service life assessment. Beginning with a discussion of what constitutes a product failure, this article then reviews four of the eight major aging mechanisms, namely environmental stress cracking, chemical degradation, creep, and fatigue, as well as the methods used in product service lifetime assessment for them. Later, several methods of service lifetime prediction that have gained industry-wide acceptance, namely the hydrostatic design basis approach, Miner's rule, the Arrhenius model, and the Paris Law for fatigue crack propagation, are discussed.

Structural alloys are commonly subjected to a variety of thermal and thermomechanical loads. This article provides an overview of the experimental methods in thermal fatigue (TF) and thermomechanical fatigue (TMF) and presents experimental results on the structural materials that have been considered in TF and TMF research. Life prediction models and constitutive equations suited for TF and TMF are covered. The structural materials discussed include carbon steels, low-alloy steels, stainless steels, aluminum alloys, and nickel-base high-temperature alloys. The article explains crack initiation and crack propagation in TF and TMF. It describes thermal ratcheting and thermal shock behavior of structural metallic materials. The article concludes with information on life prediction of structural materials under TF and TMF.

Predicting the service life of structural components involves creep-fatigue crack growth (CFCG) testing under pure creep conditions. This article provides a discussion on the loading condition and the type of ductile and brittle material showing creep behavior. It focuses on a description of the experimental method that should be followed in conducting tests of CFCG with various hold times. The article describes the testing conditions, definitions, and the necessary calculations of various crack-tip parameters considered during static and cyclic loading in time-dependent fracture mechanics. The parameters considered for static loading are C*, C(t), C*(t), C*h, Ct, and Cst(t). For cyclic loading, the parameters are delta Jc and (Ct)avg. An overview of life-prediction models is also provided.

In the design of composite structures for durability and damage tolerance, the primary concerns are out-of-plane failures, such as delamination, material degradation associated with environment, stability under compression loading, large degree of scatter in fatigue life, and bearing failure of joints. This article presents an introductory discussion on the fatigue damage process, methodologies assessing fatigue behavior, and life prediction models. It describes the damage mechanisms introduced for a quasi-isotropic laminate under tension-compression fatigue loading. Delamination is a critical issue in fatigue and generally results from high interlaminar normal and shear stresses. The article schematically illustrates the structural elements in which high interlaminar stresses are common. It concludes with a discussion on the classification of fatigue models such as mechanistic or phenomenological, for composite materials under cyclic loading.

This article summarizes fatigue phenomena in metallic materials. It discusses fatigue under variable-amplitude (VA) loading, with emphasis on crack growth. The article presents the prediction models of crack initiation and crack growth under VA loading. It concludes with a discussion on the conditions associated with engineering applications of VA loading.

This article describes the fundamental concepts of heat treatment simulation, including the physical events and their interactions, the heat treatment simulation software, and the commonly used simulation strategies. It summarizes material data needed for heat treatment simulations and discusses reliable data sources as well as experimental and computational methods for material data acquisition. The article provides information on the process data needed for accurate heat treatment simulation and the methods for their determination. Methods for validating heat treatment simulations are also discussed with an emphasis on the underlying philosophy for the selection and design of validation tests. The article also discusses the applications, capabilities, and limitations of heat treatment simulations via selected industrial case studies for a better understanding of the effect of microstructure, distortion, residual stress, and cracking in gears, shafts, and bearing rings.