Toughness assessment

EFFECT OF REMOTE HYDROGEN BOUNDARY CONDITIONS ON THE NEAR CRACK-TIP HYDROGEN CONCENTRATION PROFILES IN A CRACKED PIPELINE FRACTURE TOUGHNESS ASSESSMENT... 

Toughness assessment of ductile polymers is still a matter of debate. A sensitive way to characterise the mechanical performance of these materials, and to rank them, is to determine their ductile-brittle transitions. Test speed can thus be varied over several decades of test speed, while keeping the temperature constant, or a wide range of temperature can be scanned in controlled steps at given velocity. In the first case, the higher the speed at which the tough-to-brittle transition occurred, the better the grade in terms of fracture resistance. In the latter case, the lower the temperature at which the brittle-to-ductile transition occurred, the more suited the material for impact applications. 

Lac Lach, R., Kim, G. M., Michler, G. H., GreUmann, W., Albrecht, K. Indentation fracture mechanics for toughness assessment of PMMA/Si02 nanocomposites. Macromat. Mater. Eng. 

Mouzakis D E, Gahleitner M and Karger-Kocsis J (1998) Toughness assessment of elastomeric polypropylene (ELPP) by the essential work of fracture method, J Appl Polym Sci 70 873-881. Duhovic M, Bhattacharyya D and Fakirov S (2010) Nanofibrillar single polymer composites of poly(ethylene terephthalate), Macromol Mater Eng 294 95-99. 

Karger-Kocsis J (1996) For what kind of polymer is the toughness assessment by the essential work concept straightforward , Polym RwW 37 119-126. 

The presence of cells marks the distinctive difference between bulk composite and composite foams. The level of porosity measures the amount of empty space within the matrix and varies with foam density. For the case of syntactic foams, different microstructures or levels of porosity can be created through varying the type and amount of microspheres. Details of the microspheres used by Wouterson et al. (2007b) to prepare the epoxy syntactic foams are listed in Table 2.1. In the fracture toughness assessment under quasistatic loading, SEND specimens were loaded in a three-point bend (3PB) geometry. Due to the difference in density between the various types of microspheres, densities of foams with equivalent amounts of microspheres vary. The difference in density makes the comparison of the properties of foams nonrelevant. In order to compare the performance of foams, the specific mechanical/fracture properties are used. 

It is critical that surface treatment conditions be optimized to composite properties since overtreatment as well as undertreatment will degrade composite properties. Typically composite interlaminar shear strength (ILSS), in-plane shear, and transverse tension ate used to assess the effectiveness of surface treatment. More recently damage tolerance properties such as edge delamination strength, open hole compression, and compression after impact have become more important in evaluating the toughness of composite parts. 

What is important to realise is that a polymer may be tough when exposed to tensile load but brittle when assessed by an Izod-type test where a notched sample is subjected to a bending load. Table 9.3 attempts to summarise the behaviour of typical polymers to different stresses. 

Historically, most attention has been devoted to mode I delamination growth to assess defects critically, as the first-generation composite systems exhibited low mode I fracture toughness when subjected to interlaminar normal stresses. The... 

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