Fatigue creep

In this book no prior knowledge of plastics is assumed. Chapter 1 provides a brief introduction to the structure of plastics and it provides an insight to the way in which their unique structure affects their performance. There is a resume of the main types of plastics which are available. Chapter 2 deals with the mechanical properties of unreinforced and reinforced plastics under the general heading of deformation. The time dependent behaviour of the materials is introduced and simple design procedures are illustrated. Chapter 3 continues the discussion on properties but concentrates on fracture as caused by creep, fatigue and impact. The concepts of fracture mechanics are also introduced for reinforced and unreinforced plastics. 

An adequate description of material behavior is basic to all designing applications. Fortunately, many problems may be treated entirely within the framework of plastic s elastic material response. While even these problems may become quite complex because of geometrical and loading conditions, the linearity, reversibility, and rate independence generally applicable to elastic material description certainly eases the task of the analyst for static and dynamic loads that include conditions such as creep, fatigue, and impact. 

Long time dynamic load involves behaviors such as creep, fatigue, and impact. T vo of the most important types of long-term material behavior are more specifically viscoelastic creep and stress relaxation. Whereas stress-strain behavior usually occurs in less than one or two hours, creep and stress relaxation may continue over the entire life of the structure such as 100,000 hours or more. 

The data included provides examples of what are available. As an example static properties (tensile, flexural, etc.) and dynamic properties (creep, fatigue, impact, etc.) can range from near zero too extremely high values. They can be applied in different environments from below the surface of the earth, to over the earth, and into space. 

Berkovits, A., Relationship Between Fatigue Life in the Creep Fatigue Region Stress-Strain Response, NASA, 1988. 

Materials selection process can be depicted in terms of Figure 1.40. Materials selection involves many factors that have to be optimized for a particular application. The foremost consideration is the cost of the material and its applicability in the environmental conditions so that integrity can be maintained during the lifetime of the equipment. When the material of construction is metallic in nature, the chemical composition and the mechanical properties of the metal are significant. Some of the important mechanical properties are hardness, creep, fatigue, stiffness, compression, shear, impact, tensile strength and wear. 

Stress, temperature Thermal fatigue, creep-fatigue interaction, creep, thermomechanical fatigue, thermal process cracking, impact, graphitization, hold-time fatigue... 

This chapter provides an overview of recent advances in our understanding of the mechanics and micromechanisms of creep-fatigue crack growth in discontinuously reinforced ceramics. (Discussions of fatigue in continuously reinforced ceramics can be found in Chapter 5 of this volume.) The chapter is arranged in the following sequence. Section 7.2 begins with a description of the... 

Approaches to characterizing the creep-fatigue fracture of ceramic composites. 

Interfacial cavitation, microcracking, diffusion and crack branching due to the viscous flow of the glass phase during creep-fatigue. 

On the other hand, very high temperatures and low cyclic loading frequencies (high cycle times) promote near-tip creep-fatigue conditions where... 

Creep Crack Growth and Creep-Fatigue Crack Growth... 

The mechanical behavior of FeCo has been studied intensively since the order-disorder transition allows a direct study of the effects of ordering on the mechanical properties including creep, fatigue and... 

The work can also be extended to include the study of other properties such as creep, fatigue, shear strength, chemical resistance and electrical properties. 

The common factor to the subjects considered in this chapter is that they arc all concerned with evaluating the resistance of materials to exposure to some environmental agent other than temperature (and air). Durability involves many factors mechanical, thermal, and electrical stresses including creep, fatigue, and abrasion. These can be difficult enough to measure and are greatly complicated by the effects of nonambient temperatures, but when the effects of environments are superimposed, the problems can increase in a quantum leap. 

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