Environmental effects mechanical testing

Environmental Cracking The problem of environmental cracking of metals and their alloys is very important. Of all the failure mechanism tests, the test for stress corrosion cracking (SCC) is the most illusive. Stress corrosion is the acceleration of the rate of corrosion damage by static stress. SCC, the limiting case, is the spontaneous cracking that may result from combined effects of stress and corrosion. It is important to differentiate clearly between stress corrosion cracking and stress accelerated corrosion. Stress corro-... 

Durability in its broadest sense covers all aspects of irreversible property change with time and use. This includes all types of environmental agent that contribute to degradation and all aspects of mechanical action. This guide seeks to be comprehensive but concentrates on the most common environmental effects and the most important mechanical properties. More details of the test procedures used can be found in text books and the relevant international standards as referenced. 

Creep behaviour is a commonly used and very important measure of the effect of mechanical stress on plastics, but it is less used as a means of monitoring degradation due to environmental agents. At shorter times, the measured creep is predominantly due to physical effects and it is only at longer times that environmental effects will be apparent. It can be noted that creep tests use the same test piece at successive time intervals which is advantageous from the point of view of reproducibility. 

The main apparent technical problems posed in relation with these types of potential noise barriers would be their noise abatement capability, structural performance, fire resistance, weatherability, chemical activity, and environmental effects. To assess the quality of new products of such materials, a series of mechanical, noise abatement, and flammability tests should be performed on a number of samples from the panels made of recycled rubber products. The primary function of these panels, i.e., their noise abatement capability is among the most important aspect of their performance. 

This chapter will first discuss fracture mechanics applications to polymer composites in aerospace, and then compile the different test methods by type of load. The industiy-specific fracture mechanics test procedures for FRP composites, such as the Airbus Industries Test Method (AITM) or Boeing Support Specification (BSS), are essentially based on test procedures developed by national or international standardization agencies. This will be followed by a section with literature data to highlight selected effects of processing and material layup and type. Further sections will discuss non-unidirectional reinforcement and testing under environmental conditions that are relevant to aerospace applications, and the chapter concludes with an outlook on materials and test development trends. 

The purpose of surface preparation is to remove contamination and weak surface layers, to change the substrate surface geometry, and/or introduce new chemical groups to provide, at least in the case of metals, an oxide layer more receptive to the adhesive. An appreciation of the effects of pretreatments may be gained from surface analytical or mechanical test techniques. Experimental assessments of the effects of surface pretreatment, even when using appropriate mechanical tests, are of limited value unless environmental exposure is included. Self-stressed fracture mechanical cleavage specimens, as discussed in Chapter 4 and in the texts edited by Kinloch(2,5) for example, are therefore referred to wherever possible. 

Experimental assessments of the effects of surface pretreatment are of limited value using mechanical tests unless environmental exposure is included. It is very sound policy to collect and examine information on joints loaded and exposed to natural weathering conditions rather than depend solely on laboratory experiments. It is clear that water is the substance which causes most problems in attaining environmental stability of bonded joints interfacial failure generally indicates that a better surface pretreatment would impart improved joint performance. 

Proof of durability and safe performance are, rightly, onerous requirements for any innovations in the construction industry. The parameters affecting environmental durability have been summarised, and water has been identified as the most hostile environment for bonded joints that is commonly encountered. Identification of the general failure mechanisms is useful because it highlights the procedures necessary for the satisfactory fabrication of reliable and durable bonded joints. It also enables the development and adoption of appropriate test methods, since real joint configurations are of limited use in assessing experimentally environmental effects (e.g. bonded areas must be minimised in order to allow environmental access within a reasonable time-scale). Fracture mechanics methods. 

In Section 6.8, a detailed analysis of the most frequently used impact tests (i.e., Charpy and Izod impact tests) is used to characterize fracture toughness. Temperature, strain rate, crack tip curvature, specimen thickness, annealing, aging, irradiation, and environmental effects are discussed as test variables using the Iramework of fracture mechanics. 

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