Williams plasticity test

The recovery can be evaluated by the conventional Williams plasticity test (ASTM D926), procedure 2.2.1 at 100°C (212°F). Other tests can be used, although... 

The Williams Plastometer, which is based on this geometry, has been used in the rubber industry for many years. [I. Williams, Plasticity and its Measurement, Ind. Eng. Chem., 16, 362-364 (1931).] More recently, Leider and Bird (49) pointed out the advantage of this simple geometry for transient nonviscometric rheological testing of polymeric melts. 

A Linear Elastic Fracture Mechanics FM) Standard for Determining Kc and Gc for Plastics , Testing Protocd prepared for ESIS TC4 by J. G. Williams, 1990. 

ISO 732324 specifies a parallel plate test based on the Williams plastimeter with plates 4 cm in diameter. The test piece is 2.00 0.02 cm3 in volume and can conveniently be a cylinder 16 mm diameter and 10 mm thick. As discussed above, a close tolerance on volume is necessary for this type of plastimeter. The test piece is preheated for 15 min (the temperature of test is usually 70°C or 100°C) and compressed under a force of 49N. The thickness of the compressed test piece is measured in mm and this value multiplied by 100 quoted as the plasticity number. The preferred time of application of the force is 3 min. The correction to the standard in 2003 was to change the tolerance on the force from 0.05N to 0.5N. 

PDLCOM William Andrew, Inc., Plastics Design Library test data on the chemical compatibility and the environmental stress crack resistance of plastics... 

Hardness and apparent yield stress can be calculated from penetration test data, while sectility test data can be converted to a yield stress and a pseudo-Bingham plastic viscosity (Dixon and Williams, 1977). 

The results presented in Fig. 12 are at first sight rather surprising, since standard tests show that the fracture resistance of HIPS and other rubber-modified plastics increases with temperature. The difference between the two types of test lies in the extent of yielding. The fracture mechanics specimens were deseed to produce brittle fracture, with the minimum of yielding crack geometry, tip sharpness, specimen width, and specimen thickness were all chosen accordingly. The resistance to the initiation of brittle fracture follows the trends shown in Fig. 12. On the other hand, ductile fracture resistance increases with temperature, as the yield stress falls. Parvin and Williams measured A/c in 5 mm wide SEN cimens, and found that toughness increased with temperature above —60 °C. 

Applications of linear elastic fracture mechanics (primarily) to the brittle fracture of solid polymers is discussed by Professor Williams. For those not versed in the theory of fracture mechanics, this paper should serve as an excellent introduction to the subject. The basic theory is developed and several variants are then introduced to deal with weak time dependence in solid polymers. Previously unpublished calculations on failure times and craze growth are presented. Within the framework of brittle fracture mechanics and testing this paper provides for a systematic approach to the faOure of engineering plastics. 

The position of a sample of plastic in a beaker of a test liquid with known density at a particular temperature is related to the density of the plastic. The density of water at 20°C is 1 gcm . If a small sample floats on the surface of the water, it has a density lower than 1 gcm at the same temperature. If it is suspended, the density of the plastic is 1 gcm and if it sinks the plastic has a higher density. Polyethylene, polypropylene and polystyrene float on water while other plastics sink (Figure 5.4). Samples of plastic films may be taken using a hole punch, but this technique is unsuitable for foams or blocks of material (Williams et al., 1998). Other fluids used include saturated sodium chloride (1.20gcm ), saturated magnesium chloride (1.34gcm ), saturated calcium chloride (1.45gcm ) and saturated zinc chloride (1.57-2.00 gcm ). 

Williams (49), Ward (79), and Jancar et al. (89) proposed an approximate model of mixed mode of fracture to account for the effect of finite specimen dimensions for Kc and G, respectively. The basic idea in both theories is a substitution of the actual distribution of fracture toughness across the cross-section by a simple bimodal distribution, assuming plane strain value in the center and plane stress value at the surface area of the specimen. Size of the plastic zone IR relative to the specimen width B gives the contribution of plane stress regions and is a measure of the displacement of the state of stress at the crack tip from the plane strain conditions. Note that this approach can be used only if the mode of failure does not change with the test conditions or material composition (i.e., it attains its brittle character). 

European Structural Integrity Society (ESIS) Testing Committee protocol for conducting J-crack growth resistance curve tests on plastics, in D. R. Moore, B. R. K. Blackman, P. Davies, A. Pavan, P. Reed, J. G. Williams, eds., Experimental Methods in the Application of Fracture Mechanics Principles to the Testing of Polymers, Adhesives and Composites, Elsevier, London, 2000, p. 140. 

S.Hashemi and J.G. Williams, Testing of Polymers, VI Int. Conf. on Deformation Yield and Fracture of Polymers, Cambridge, April 1985, The Plastic and Rubber Institute (Chameleon Press Ltd.) 1985, 531. 

Williams, J.C. (2001). Introduction to elastic-plastic fracture mechanics. In Fracture mechanics testing methods for polymers, adheswes and composites, Moore, D.R. Pavan, A. Williams J.C., (Eds.), pp 119-122, Elsevier Science Ltd. and ESIS, ISBN 0 08 043689 7, The Netherlands. 

Williams, J.G., Root rotation and plastic work effects in the peel test. J. Adhes., 41, 225-239 (1993). 

Firstly, Moore and Williams [55J have reported results from T-peel tests using the five-layer structure laminate discussed above. The values of Gc were obtained from T-peel tests via the above analytical method, allowing for plastic bending of the peel arms. (Thus, measurement of the angles 9 and 62, see Fig. 3, was also undertaken since they are required for the plastic-bending analysis.) The results from the T-peel and the fixed-arm peel test, where the peel angle was varied as discussed above, were not significantly different. 

The plastic bending in the fixed-arm peel test can be modeled using large-displacement beam theory with modifications for plastic bending (Kinloch and Williams 2002). Much of the development of the correction procedures has focused on how the stress-strain behavior of the peel arm is treated. Indeed, solutions have been formulated for three cases the various... 

A plot of An over BD0 should give, therefore, a straight line with slope R = Gc-Testing nine different brittle and ductile polymers (from PS to PE) by the Charpy and the Izod methods, Plati and Williams [64] were able to arrive at fairly unique values of Gc (cf. Table 9.2). They point out, however, that in order to obtain linear BD0 plots they had to consider an effective crack length consisting of the initial crack length and the size of a suitably chosen plastic zone. 

Reference Pavan, A. and Williams, J. G., Development of a Standard for Determining K,< and G,c for Plastics at High Loading Rates the ESIS Protocol for 1 m/s Testing, Limitations of Test Methods for Plastics, ASTM STP1369, J. S. Peraro, Ed., American Society for Testing and Materials, West Conshohocken, PA, 2000. 

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