Electron spin resonance (ESR), or electron paramagnetic resonance (EPR), is an analytical technique that can extract a great deal of information from any material containing unpaired electrons. This article explains how ESR works and where it applies in materials characterization. It describes a typical ESR spectrometer and explains how to tune it to optimize critical electromagnetic interactions in the test sample. It also identifies compounds and elements most suited for ESR analysis and explains how to extract supplementary information from test samples based on the time it takes electrons to return to equilibrium from their resonant state. Two of the most common methods for measuring this relaxation time are presented as are several application examples.

This article discusses the attempts made by the industry to create sensing approaches for modeling a process, part, and chemistry and kinetics. It reviews microwave curing of thick-section composites and the resin cure sensors that are used for resin cure monitoring. These include dielectric cure sensors, fiberoptics-based resin cure sensors, ultrasonics-based resin cure sensors, and dosimetry-based resin cure sensors. The article provides information on the resin cure control flow sensing, flow modeling, flow mapping, and resin flow. It addresses some practical issues in sensing resin cure and flow.

Nuclear magnetic resonance (NMR) is a form of radio frequency spectroscopy based on interactions between nuclear magnetic dipole or electric quadrupole moments and an applied magnetic field or electric-field gradient. This article provides an overview of the fundamental principles of nuclear magnetic resonance with emphasis on nuclei properties, the basic equation of nuclear magnetic resonance, the classical theory of nuclear magnetization, line broadening, and measurement sensitivity. It describes the pulse-echo method for observing NMR. The article provides useful information on ferromagnetic nuclear resonance and nuclear quadrupole resonance, and illustrates the experimental arrangement of NMR with a block diagram. It also presents several application examples.

This article describes the general aspects of creep, stress relaxation, and yielding for homogeneous polymers. It then presents creep failure mechanisms in polymers. The article discusses extrapolative methods for the prediction of long-term creep failure in polymer materials. Then, the widely used models to simulate the service life of polymers are highlighted. These include the Burgers power-law model, the Findley power-law model, the time-temperature superposition (or equivalence) principle (TTSP), and the time-stress superposition principle (TSSP). The Larson-Miller parametric method, one of the most common to describe the material deformation and rupture time, is also discussed.

This article describes the viscoelastic behavior of plastics in their solid state only, from the standpoint of the material deforming without fracturing. The consequences of viscoelasticity on the mechanical properties of plastics are described, especially in terms of time-dependencies, as well as the dependence of the viscoelastic character of a plastic on chemical, physical, and compositional variables. By examining the viscoelastic behavior of plastics, the information obtained are then applied in situations in which it may be important to anticipate the long-term properties of a material. This includes assessing the extent of stress decay in materials that are pre-stressed, the noise and vibration transmission characteristics of a material, the amount of heat build-up in a material subjected to cyclic deformation, and the extent a material can recover from any prior deformation. Several qualitative graphs are presented, which highlights the possible differences in the viscoelastic behavior that can exist among plastics.

The key to any successful part development is the proper choice of material, process, and design matched to the part performance requirements. Understanding the true effects of time, temperature, and rate of loading on material performance can make the difference between a successful application and catastrophic failure. This article provides examples of reliable material performance indicators and common practices to avoid failure. Simple tools and techniques for predicting part mechanical performance integrated with manufacturing concerns, such as flow length and cycle time, are demonstrated. The article describes the prediction of mechanical part performance for stiffness, strength/impact, creep/stress relaxation, and fatigue.

Hyperthermia is a type of cancer treatment that requires directing a carefully controlled dose of heated nanoparticles to the cancerous tumor that leads to the destruction of cancer cells. Nanoparticles are used as the heat generating sources within the cancer cells and the tumors. The problem in controlling the temperature of nanoparticles is solved by the use of induction heating, which uses a high-frequency alternating magnetic field localized in the area of interest. This article provides an overview of this technique along with the description of its major components, namely, nanoparticles, induction heating setup, and magnetic field strength.

This article provides some new developments in elevated-temperature and life assessments. It is aimed at providing an overview of the damage mechanisms of concern, with a focus on creep, and the methodologies for design and in-service assessment of components operating at elevated temperatures. The article describes the stages of the creep curve, discusses processes involved in the extrapolation of creep data, and summarizes notable creep constitutive models and continuum damage mechanics models. It demonstrates the effects of stress relaxation and redistribution on the remaining life and discusses the Monkman-Grant relationship and multiaxiality. The article further provides information on high-temperature metallurgical changes and high-temperature hydrogen attack and the steps involved in the remaining-life prediction of high-temperature components. It presents case studies on heater tube creep testing and remaining-life assessment, and pressure vessel time-dependent stress analysis showing the effect of stress relaxation at hot spots.

Engineering plastics, as a general class of materials, are prone to the development of internal stresses which arise during processing or during servicing when parts are exposed to environments that impose deformation and/or temperature extremes. Thermal stresses are largely a consequence of high coefficients of thermal expansion and low thermal diffusivities. Although time-consuming techniques can be used to analyze thermal stresses, several useful qualitative tests are described in this article. The classification of internal stresses in plastic parts is covered. The article describes the effects of low thermal diffusivity and high thermal expansion properties, and the variation of mechanical properties with temperature. It discusses the combined effects of thermal stresses and orientation that result from processing conditions. The article also describes the effect of aging on properties of plastics. It explains the use of high-modulus graphite fibers in amorphous polymers.

This article discusses stress relaxation testing on metallic materials, as covered by ASTM E 328. It reviews the two types of stress relaxation tests performed in tension, long-term and accelerated testing. The article illustrates load characteristics and data representation for stress relaxation testing used for the most convenient and common uniaxial tensile test. It concludes with information on compression testing, bend testing, torsion testing, and tests on springs.

Copper and copper alloys are used extensively in structural applications in which they are subject to moderately elevated temperatures. At relatively low operating temperatures, these alloys can undergo thermal softening or stress relaxation, which can lead to service failures. This article is a collection of curves and tables that present data on thermal softening and stress-relaxation in copper and copper alloys. Thermal softening occurs over extended periods at temperatures lower than those inducing recrystallization in commercial heat treatments. Stress relaxation occurs because of the transformation of elastic strain in the material to plastic, or permanent strain.

This article discusses the deformation and viscoelastic characteristics of plastics as polymeric materials, focusing on the test methods used for the evaluation of their mechanical properties, methods available for analytically predicting the deformation response of polymers, and the effect of viscoelasticity on the test methods used. Two common ways of evaluating viscoelasticity of plastics are by means of creep experiments and dynamic mechanical experiments. Graphic or tabular analysis of test data, time-temperature superposition, and empirical correlation methods are commonly employed for analytical prediction of deformation characteristics of polymers.

Compared to cold-formed parts, age-formed parts have lower residual stresses and consequently better stress corrosion resistance. This article addresses the technical issues that arise in the investigations of creep in precipitate-strengthened materials. The issues addressed help in developing alloys and tempers particularly suited for the age-forming process. The different steps involved in the program for predicting the final part shape are discussed. These basic steps involve developing mechanical tests to study creep at low temperatures and low stresses, describing low-temperature creep in terms of a constitutive model, and then using the constitutive model in a process model or finite element analysis to predict the final part shape.

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 reviews the basic mechanisms of elevated-temperature behavior and associated design considerations, with an emphasis on metals. It discusses the key concepts of elevated-temperature design. These include plastic instability at elevated temperatures; deformation mechanisms and strain components associated with creep processes; stress and temperature dependence; fracture at elevated temperatures; and environmental effects. The article describes the basic presentation and analysis methods for creep rupture. It provides information on the application of these methods to materials selection and the setting of basic design rules. The article examines the limitations of high-temperature components as well as the alternative design approaches and tests for most high-temperature components.