Search

Abstract: This study explores three approaches to determining plane-strain fracture toughness of high-density polyethylene (HDPE), based on the concept of essential work of fracture (EWF). The first approach adopted the traditional method that uses total energy consumed in the testing to determine the plane-strain fracture toughness. The second and the third approaches used energy-partitioning principles to exclude the energy consumption in a later stage of the testing from the calculation of the EWF value. The 2nd approach used a new energy partitioning scheme that excluded the energy consumed at the last stage of plastic deformation; and the 3rd approach was based on an existing energy partitioning scheme proposed by another group, to exclude the energy consumption after the maximum load was reached. The results show that only the 2nd approach generates the EWF value that is independent of the specimen thickness. The paper recommends that the 2nd approach be the most suitable method for determining the plane-strain fracture toughness for ductile polymers like HDPE. [Copyright &y& Elsevier]

Abstract: This paper presents a new test method that measures fracture toughness of polymeric materials when subjected to in-plane shear loading (mode II), and compares the toughness with that in tension mode (mode I). The new test method uses an Iosipescu device to apply the shear load, and determines the toughness based on the concept of essential work of fracture (EWF). Three physical-based criteria were used to verify the occurrence of mode II fracture. The new test method was then used to evaluate toughness of poly(acrylonitrile–butadiene–styrene) (ABS). The results suggest that for the ABS, the ratio of toughness in mode II to mode I is about 2.5 which leads to the dominance of mode I fracture in most loading conditions. The results also showed that for ABS in mode I fracture, the specific work of fracture (defined as the absorbed energy for fracture divided by the cross sectional area of the ligament between the notch tips) depends on ligament length; while in mode II fracture, it depends on ligament thickness. The study concludes that the new test method has a good potential for evaluation of mode II fracture toughness of polymers, though further study using polymers of different characteristics will be needed to confirm universality of the test method in the measurement of mode II fracture toughness. [Copyright &y& Elsevier]

Toughness variation of non-notched poly(acrylonitrile-butadiene-styrene) (ABS) subjected to uniaxial fatigue loading was investigated. The experiments were conducted by applying fatigue loading to strip specimens first from which dog-bone specimens were machined. The dog-bone specimens were tested to measure the strain for the on-set of fracture, named cracking strain here, thus to monitor the toughness change due to the fatigue loading. The test results showed that the fatigue loading caused the toughness drop in ABS, even before any visible crack was developed. Damage development and fracture behavior were then analyzed using scanning electron microscopy (SEM). The SEM analysis revealed that damage zones, not cracks, were initiated during the fatigue loading, and were the main cause of the toughness drop. Mechanisms for the damage initiation include matrix crazing and debonding of small rubber particles; however, large rubber particles remained intact. Based on the results, a deformation model is proposed for the damage zone initiation, which provides an explanation for the toughness change under the fatigue loading. [ABSTRACT FROM AUTHOR]