Polymeric materials failure analysis

With increasing use of polymeric materials in industry the corrosion engineer is faced with the need to have knowledge of the basic types of polymers, their characteristic features, modes of failure of polymeric components and the methods involved in characterization of polymers in failure analysis. Some characteristics of engineering polymers are as follows ... 

The various methods used in failure analysis of polymeric materials are noted below ... 

Analysis of these effects is difficult and time consuming. Much recent work has utilized two-dimensional, finite-difference computer codes which require as input extensive material properties, e.g., yield and failure criteria, and constitutive laws. These codes solve the equations of motion for boundary conditions corresponding to given impact geometry and velocities. They have been widely and successfully used to predict the response of metals to high rate impact (2), but extension of this technique to polymeric materials has not been totally successful, partly because of the necessity to incorporate rate effects into the material properties. In this work we examined the strain rate and temperature sensitivity of the yield and fracture behavior of a series of rubber-modified acrylic materials. These materials have commercial and military importance for impact protection since as much as a twofold improvement in high rate impact resistance can be achieved with the proper rubber content. The objective of the study was to develop rate-sensitive yield and failure criteria in a form which could be incorporated into the computer codes. Other material properties (such as the influence of a hydrostatic pressure component on yield and failure and the relaxation spectra necessary to define viscoelastic wave propagation) are necssary before the material description is complete, but these areas will be left for later papers. 

Polymers mechanical properties are some from the most important, since even for polynners of different special purpose functions this properties certain level is required [199], However, polymiers structure complexity and due to this such structure quantitative model absence make it difficult to predict polymiers mechanical properties on the whole diagram stress-strain (o-e) length—fi-om elasticity section up to failure. Nevertheless, the development in the last years of fractal analysis methods in respect to polymeric materials [200] and the cluster model of polymers amorphous state structure [106, 107], operating by the local order notion, allows one to solve this problem with precision, sufficient for practical applications [201]. 

In many laboratories, MALDI-MS has become a routine tool for polymer characterization. This is evident from an increasing number of pubUcations in polymer Uterature (i.e., Macromolecules) which indicate the use of MALDI-MS as a tool for characterizing newly grafted or synthesized polymers. In an industry deaUng with polymeric materials, MALDI-MS is often combined with other analytical techniques to provide detailed analyzes of a polymeric system. In some cases, MALDI-MS is the only technique that can provide the information required to solve a practical problem. One example is in the area of product failure analysis... 

Riga [57] comments that a TMA has been used as a tool in many diverse projects, such as quality control, verification of standards, failure analysis, and characterisation of polymeric materials. 

The various techniques in the realm of thermal analysis have a variety of uses in quality control testing, R D, and failure investigations of insoluble or carbon-black containing polymeric materials, such as rubbers. 

There is a growing interest in the investigation of iled materials. Since long time ago, a lot of efforts have been devoted to the analysis of failures in metallic parts and structures. Some recent texts are focused in post-failure analysis of polymeric materials (Lewis and Gagg 2010) and polymer composite (Greenhalgh 2009). Most adhesives are polymers, and they are used nowadays in an uncountable number of applications in everyday Kfe, especially applications where a failure in service may lead to economic loss, injury, or death. The ability to determine the cause of failure using forensic engineering techniques is essential. 

In this chapter an overview of conceptually different fracture theories is presented which have in common that they do not make explicite reference to the characteristic properties of the molecular chains, their configurational and super-molecular order and their thermal and mechanical interaction. This will be seen to apply to the classical failure criteria and general continuum mechanical models. Rate process fracture theories take into consideration the viscoelastic behavior of polymeric materials but do not derive their fracture criteria from detailed morphological analysis. These basic theories are invaluable, however, to elucidate statistical, non-morphological, or continuum mechanical aspects of the fracture process. 

Most adhesives are polymer-based materials and exhibit viscoelastic behavior. Some adhesives are elastomer materials and also exhibit full or partial rubberlike properties. The word elastic refers to the ability of a material to return to its original dimensions when unloaded, and the term mer refers to the polymeric molecular makeup in the word elastomer. In cases where brittle material behavior prevails, and especially, when inherent material flaws such as cracks, voids, and disbonds exist in such materials, the use of the methods of fracture mechanics are called for. For continuum behavior, however, the use of damage models is considered appropriate in order to be able to model the progression of distributed and non-catastrophic failures and/or irreversible changes in material s microstructure, which are sometimes described as elastic Hmit, yield, plastic flow, stress whitening, and strain hardening. Many adhesive materials are composite materials due to the presence of secondary phases such as fillers and carriers. Consequently, accurate analysis and modeling of such composite adhesives require the use of the methods of composite materials. 

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