On the essential work of ductile fracture in polymers

Abstract

The essential work of fracture concept has been extended to cover ductile tearing of polymeric materials that neck before fracture. It is shown that the plane stress specific essential fracture work (w e) can be obtained from deeply edge-notched tension specimens, containing either single or double notches, by extrapolating the straight line relationship between the total specific fracture work (Wy) and ligament length (1) to zero ligament. In this way, specific essential fracture works have been obtained for nylon 66 and two polyethylenes. It seems that w e is a material property for a given sheet thickness being independent of specimen geometry. The straight line relationship between w / a n d / breaks down when the ligament length to sheet thickness ratio is less than about three, since the fracture data fall in the plane stress-plane strain transition region. However, a plane strain specific essential fracture work can still be obtained by extrapolating the least squares curve of the data to zero ligament provided the thickness satisfies plane strain condition. If this condition is not satisfied a near plane strain value is obtained which is dependent upon thickness. This method is also appropriate for ductile polymers like the rubber modified polystyrenes that craze rather than neck.JR curves have also been obtained for nylon 66 and the polyethylenes. Under strictly J-controlled crack growth conditions, it is shown that the intercept and slope of the JR curve, i.e. Jc and dJ/da, are related to the intercept and slope of the w/versus l plot. The limited amounts of J-controlled data available have precluded a more definite and general conclusion to be made. But based on what little is available, the comparisons of these two quantities in the J R -Aa and w / -1 plots are. not unreasonable.

The Essential Work of Fracture of Thermoplastic Orthodontic Retainer Materials

“…In response, the Essential Work of Fracture (EWF) Test was recently developed to evaluate the fracture toughness of ductile, thin, plastic sheets. 3,4 In the most frequently used EWF test, which uses a double-edge-notched-tension specimen, a series of specimens with equal thicknesses (t) and systematically different internotch distances, or ligament lengths (Ls), are each loaded in tension until complete fracture occurs ( Figure 1A). Integrating the area under the load-elongation curve generated during testing of each specimen yields that specimen's total work of fracture (W f ), representing the energy needed for complete specimen fracture ( Figure 1B).…”

“…In EWF theory, W f is divided into two components: essential work and nonessential work. 3 The EWF, or W e , is the energy that is ''essential'' in generating new fracture surfaces. This energy is concentrated near the plane of fracture and crack tip.…”

Fracture development and deformation behavior of zeolite-filled high density polyethylene annealed composites in the plane stress fracture

“…The earlier process in data deduction has been considerably used for DENT test, which is based on some of the following assumptions in the determination of essential fracture work parameter: (i) plastic zones evolved fully around the ligament region prior to crack growth, (ii) the necking take place within FPZ, and (iii) fracture strain rate in the FPZ is constant during crack growth [11,[28][29][30]. The strain hardening may not be enough to produce stable neck correspond to the later two assumptions.…”

“…To ensure that the plane-stress fracture occurred, the DENT specimens used as shown in Fig. 1 were prepared to have a width (W) of 50 mm and the initial ligament length (ℓ) ranging from 9 to 15 mm (corresponding to 3-5 times to t), according to suggested value by many researchers [6,11,12].…”

“…Nevertheless, in the case of ductile materials such as zeolite-reinforced HDPE, the strainhardening rate in the neck is quick sufficient to offset the reduction in cross-sectional area, so that the process of neck development is stable, and its size is growing at a fixed rate [10]. Previous studies evaluating the EWF of polyethylene such as HDPE [6,11,12] have neglected the process of neck developing in analyzing the energy needed during the fracture. In contrast to those studies, Jar and co-workers [13,14] have observed neck formation during fracture process and reported that in plane stress fracture of DENT specimen, the neck was initiated along the ligament part, it spread to adjacent areas which had been deformed at an early step of the test.…”