Search Results for transient thermal stress

During fusion welding, the thermal cycles produced by the moving heat source cause physical state changes, metallurgical phase transformation, and transient thermal stress and metal movement. This article presents an analysis of heat flow in the fusion welding process. The primary objective of welding heat flow modeling is to provide a mathematical tool for thermal data analysis, design iterations, or the systematic investigation of the thermal characteristics of any welding parameters. The article addresses analytical heat-flow solutions and their practical applications. It describes the effects of material property and welding condition on the temperature distribution of weldments. The thermal properties of selected engineering materials are provided in a table.

This article describes the formation of residual stresses and distortion, providing information on the techniques for measuring residual stresses. It presents a detailed discussion on the magnitude and distribution analysis of the residual stresses and distortion in weldments. The article briefly explains the effects of residual stresses and distortion on the brittle fracture and fatigue fracture of welded structures. It also provides information on the thermal treatments of weldments.

This article describes the formation of residual stresses and distortion and the techniques for measuring residual stresses. It provides a discussion on the magnitude and distribution analysis of residual stresses and distortion in weldments. The article considers the effects of residual stresses and distortion on the brittle fracture and fatigue fracture of welded structures. The thermal treatments of weldments are also discussed.

Thermal nondestructive evaluation (TNDE) is an indirect process, so that regardless of the form of energy used to excite the sample, interaction with the internal structure of a part occurs through the process of heat conduction. This article discusses the steady-state configuration and selective excitation configuration of the signal-generation mechanisms in thermal nondestructive evaluation methods. The three widely used approaches to TNDE are surface-excited thermography, vibrothermography, and thermoelastic stress analysis. The article provides information on the common features, characteristics, and limitations of these approaches.

Thermomechanical fatigue (TMF) refers to the process of fatigue damage under simultaneous changes in temperature and mechanical strain. This article reviews the process of TMF with a practical example of life assessment. It describes TMF damages caused due to two possible types of loading: in-phase and out-of-phase cycling. The article illustrates the ways in which damage can interact at high and low temperatures and the development of microstructurally based models in parametric form. It presents a case study of the prediction of residual life in a turbine casing of a ship through stress analysis and fracture mechanics analyses of the casing.

The design process for ceramic materials is more complex than that of metals because of low-strain tolerance, low fracture toughness and brittleness. The application of structural ceramics to engineering systems hinges on the functional benefits to be derived and is manifested in the conceptual design for acceptable reliability. This article discusses the design considerations for the use of structural ceramics for engineering applications. It describes the conceptual design and deals with fast fracture reliability, lifetime reliability, joints, attachments, interfaces, and thermal shock in detailed design procedure. The article provides information on the proof testing of ceramics, and presents a short note on public domain software that helps determine the reliability of a loaded ceramic component. The article concludes with several design scenarios for gas turbine components, turbine wheels, ceramic valves, and sliding parts.

This article provides information on the development of finite element analysis (FEA) and describes the general-purpose applications of FEA software programs in structural and thermal, static and transient, and linear and nonlinear analyses. It discusses special-purpose finite element applications in piping and pressure vessel analysis, impact analysis, and microelectronics. The article describes the steps involved in the design process using the FEA. It concludes with two case histories that involve the use of FEA in failure analysis.

The finished product, after fusion welding, may contain physical discontinuities due to excessively rapid solidification, adverse microstructures due to inappropriate cooling, or residual stress and distortion due to the existence of incompatible plastic strains. To analyze these problems, this article presents an analysis of the welding heat flow, with focus on the fusion welding process. It discusses the analytical heat-flow solutions and their practical applications. The article concludes with a description of the effects of material property and welding condition on the temperature distribution of weldments.

When complex designs, transient loadings, and nonlinear material behavior must be evaluated, computer-based techniques are used. This is where the finite-element analysis (FEA) is most applicable and provides considerable assistance in design analysis as well as failure analysis. This article provides a general view on the applicability of finite-element modeling in conducting analyses of failed components. It highlights the uses of finite-element modeling in the area of failure analysis and design, with emphasis on structural analysis. The discussion covers the general development and both general- and special-purpose applications of FEA. The special-purpose applications of FEA covered are piping and pressure vessel analysis, impact analysis, and microelectronic and microelectromechanical systems analysis. The article provides case histories that involved the use of FEA in failure analysis.

This article summarizes many approaches that are used to simulate relaxation of bulk residual stresses in components. It presents analytical examples to highlight the complexity of residual stress and strain distributions observed in simple geometries, with ideal material behavior and trivial loading and boundary conditions. The article discusses approximate and advanced solution techniques that can be employed in practice for simulation of residual stress relief: finite-difference method and finite-element method. It also describes advanced techniques applicable to transient creep, advanced constitutive models, and complicated stress and temperature loading histories.

This article introduces the fundamental sources of residual stresses common to most manufacturing processes. It explains the effect of material removal on residual stresses and distortions in a part. The article assists the reader in making a choice between trial-and-error and computer-simulation approaches for the control of residual stresses. It provides a summary of the commonly used techniques of measuring residual stresses. The article also describes the finite element method for predicting residual stresses caused by various manufacturing processes. It concludes with a discussion on the operations involved in thermal and mechanical stress-relief methods.

This article is a comprehensive collection of formulas and numerical solutions, addressing many heat-transfer scenarios encountered in welds. It provides detailed explanations and dimensioned drawings in order to discuss the geometry of weld models, transfer of energy and heat in welds, microstructure evaluation, thermal stress analysis, and fluid flow in the weld pool.

This article focuses on the concepts involved in heat-transfer modeling, thermomechanical modeling, and microsegregation modeling of hot tearing. It discusses the modeling of solidification defects, namely, inclusion entrapment, segregation, shrinkage cavities, gas porosity, mold-wall erosion, and hot-tear cracks.

Intensive quenching (IQ) is an alternative method of hardening steel parts. Two types of IQ methods are used in heat treating practice: IQ-2 and IQ-3. IQ-2 is implemented in IQ water tanks, which are usually used for batch quenching of steel parts. IQ-3 is conducted in single-part processing using high-velocity water flow IQ units. This article presents a detailed description of IQ technology, related equipment, and IQ applications. A review of intensive quench system design and processing is provided, including numerical design criteria, steel selection, quenchants, properties (especially optimal residual stress profiles). Several specific applications of intensive quenching are also provided.

This article focuses on the necessary basics for thermomechanical fusion welding simulations and provides an overview of the specific aspects to be considered for a simulation project. These aspects include the required material properties, experimental data needed for validation of the simulation results, simplifications and assumptions as a prerequisite for modeling, and thermomechanical simulation. The article concludes with information on the sensitivity of the material properties data with respect to the simulation results. It also provides hints on the central challenge of having the right material properties at hand for a specific simulation task.

This article focuses on the various assumptions involved in the numerical modeling of welds, including the geometry of the welded structure and the weld joint, thermal stress, strain, residual stress, and the microstructure in the heat-affected and fusion zones.

In cast iron, residual stresses normally arise due to hindered thermal contraction, meaning that they are associated with the presence of constraints that prevent the natural, free volumetric variation of the material upon solid-state cooling. This article explains their mechanism of formation by introducing the scalar relation, known as the additive strain decomposition. The main factors influencing casting deformation are volume changes during solidification and cooling, phase transformations, alloy composition, thermal gradients, casting geometry, and mold stability. The article reviews the dimensional stability in cast iron and discusses macroscopic and microscopic stresses in cast iron.

This article provides a detailed overview of the thermomechanical modeling of additive manufacturing (AM) process. It begins with information on a basic understanding of the formation of residual stress during AM processing followed by a discussion on models commonly applied in AM modeling, such as heat-input models, material models, and material activation models. Information on experimental setup for validation and simulation of directed-energy deposition model is then included. The article also provides information on moving-source and part-scale analyses to simulate the laser powder-bed fusion AM process.

Thermomechanical fatigue (TMF) is the general term given to the material damage accumulation process that occurs with simultaneous changes in temperature and mechanical loading. TMF may couple cyclic inelastic deformation accumulation, temperature-assisted diffusion within the material, temperature-assisted grain-boundary evolution, and temperature-driven surface oxidation, among other things. This article discusses some of the major aspects and challenges of dealing with TMF life prediction. It describes the damage mechanisms of TMF and covers various experimental techniques to promote TMF damage mechanisms and elucidate mechanism coupling interactions. In addition, life modeling in TMF conditions and a practical application of TMF life prediction are presented.

Thermal phenomena play a key role in the mechanics of surface finishing processes. This article provides information on the analysis and measurement of temperatures and associated thermal damage generated by finishing processes that are essential to the production of engineered components with controlled surface properties. Emphasis is placed on kinematically simple configurations of finishing processes, such as surface grinding, flat surface polishing, and lapping.