Plane strain fracture toughness testing of high density polyethylene
01 Oct 1981-Polymer Engineering and Science (Society of Plastics Engineers, Inc.)-Vol. 21, Iss: 15, pp 1019-1026
TL;DR: In this paper, the concepts of linear elastic fracture mechanics (LEFM) were applied to three grades of high density polyethylene in an attempt to determine their fracture behavior in terms of a plane strain fracture toughness, Kc.
Abstract: The concepts of linear elastic fracture mechanics (LEFM) are applied to three grades of high density polyethylene in an attempt to determine their fracture behavior in terms of a linear elastic fracture toughness, Kc. The effect of specimen size (thickness and width), crack length and the mode of loading on Kc has been investigated in order to determine the plane strain fracture toughness, KIc, of these materials. The effect of temperature (between +23 and −180°C) on their fracture behavior has also been investigated and compared in terms of their plane strain fracture toughness values.
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TL;DR: In this article, an outline of the characteristics of PEEK and the versatility of its compositional forms (micro and macro composites) are given to illustrate its wide potential for success in engineering applications.
262 citations
TL;DR: In this article, a commercial polybutylene terephthalate/polycarbonate/impact modifier (PBT/PC/IM) blend was used to study the fracture mechanisms involved at different temperatures under both impact and static loading.
Abstract: Scanning electron microscopy (SEM) and transmission electron microscopy (TEM) techniques were employed in the morphology and fracture mechanisms studies on a commercial polybutylene terephthalate/polycarbonate/impact modifier (PBT/PC/IM) blend. The fracture mechanisms involved at different temperatures under both impact and static loading were revealed. It was found that massive plastic deformation of the matrix material occurred after rubber particle cavitation; and it was this plastic deformation that was responsible for the drastic enhancement in fracture toughness although the widespread cavitation did absorb a considerable amount of energy as well. The major source of toughness was the same for both impact and static fracture tests, but the toughening processes became effective at a much lower temperature under static than impact conditions. The sequence of toughening events was also observed using TEM.
149 citations
TL;DR: In this paper, the authors investigated the phenomenon of slow stable crack growth in polyethylene using notched specimens subject to constant load and the concepts of fracture mechanics and demonstrated that Kc is the controlling stress parameter for crack growth under suitable conditions.
133 citations
TL;DR: Fracture mechanics tests on two low density polyethylenes and two linear low-density polyethylene are described in this article, showing that at temperatures < 0°C crack growth occurs.
83 citations
TL;DR: In this article, the use of the J method to characterize fracture is described, and it is noted that smaller specimens may be used to obtain plane strain values than in conventional linear elastic fracture mechanics (LEFM) tests.
Abstract: The use of the J method to characterize fracture is described, and it is noted that smaller specimens may be used to obtain plane strain values than in conventional linear elastic fracture mechanics (LEFM) tests. Various methods of computing J are described, and the extrapolations necessary to define crack initiation are discussed. The various schemes and size criteria are then explored for a polypropylene copolymer, and it is found that the recommended ASTM procedure using energy works well. The method is then used to characterize several toughened polymers, and some discussion of the slope of the resistance curve is given.
73 citations
References
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TL;DR: In this article, the authors made a calculation of the length of plastic zone needed to accommodate a given plastic displacement at the root of a notch in a uniformly stressed solid, and concluded that a condition of ''far-reaching'' yield should replace the condition of general yield for starting a fracture.
Abstract: A calculation is made of the length of plastic zone needed to accommodate a given plastic displacement at the root of a notch in a uniformly stressed solid. In an optimum range of stress this zone is about 1000 times larger than the plastic displacement and about five times longer than the notch. The distribution of plastic-elastic strain in the yielded region can be represented by an inverted pile-up of dislocations. The results are related to the problem of notch-brittleness in steel and it is concluded that a condition of `far-reaching' yield should replace the condition of general yield for starting a fracture. Various factors important to notch-brittleness are briefly discussed.
849 citations
TL;DR: In this article, theoretical plane-strain solutions for the initial plastic yielding of notched bars with either a V notch or a notch whose root is a circular arc are presented.
Abstract: T heoretical plane-strain solutions are presented for the initial plastic yielding of notched bars bent either under four-point loading or as in the Izod or Charpy tests, and having either a V notch or a notch whose root is a circular arc. These solutions provide estimates of the stresses in the plastic regions, the mode of yielding, and the corresponding yield-point loads. Calculations are made of the maximum tensile stress below the notch root and of the smallest depth of notch for which initial yielding does not extend to the notched surface. The theoretical solutions are confirmed by experimental observations of the yield-point loads in slow bend tests, and of the modes of deformation in slow and impact tests ; the latter are found to be very similar. The ductility transition is discussed in relation to this and other work.
273 citations
TL;DR: In this article, the fracture toughness of polycarbonate was obtained over the temperature range 20 to − 120° C. This change is associated with the β transition and stable crack growth was observed in this region with accompanying instabilities arising from adiabatic heating at the crack tip.
Abstract: The fracture toughness of polycarbonate was obtained over the temperature range 20 to − 120° C. There is a strong thickness dependence which is described in terms of plane stress and plane strain values which are insensitive to temperatures above −40° C but the plane stress value increases below this temperature. This change is associated with theβ transition and stable crack growth was observed in this region with accompanying instabilities arising from adiabatic heating at the crack tip.
117 citations
TL;DR: In this article, the authors applied linear elastic fracture mechanics (LEFM) to polypropylene, a homopolymer and two copolymers, with a view to characterizing their brittle behavior at slow rates (0.5 cm/min) in terms of a fracture toughness, KIc.
Abstract: The concepts of Linear Elastic Fracture Mechanics (LEFM) are applied to polypropylene, a homopolymer and two copolymers, with a view to characterizing their brittle behavior at slow rates (0.5 cm/min) in terms of a fracture toughness, KIc. The effect of thickness, notch sharpness, and the mode of loading on KIc have been investigated in order to determine the plane strain toughness values, KcI for the materials. The two types of material are compared in terms of their toughness values over a range of temperatures between +30 and −160°C. Evidently, the small amounts of ethylene added to the copolymers show plasticizing effects, suppressing the yield stress and the ductile-brittle transition temperature. In addition, the copolymers exhibit a ductile-brittle region between −100 and −45°C where notch strengthening is apparent in the tension mode and a slow crack growth region between −45 and −30°C where slow growth precedes unstable fracture. The homopolymer, however, shows no clear evidence of such intermediate regions, except for slight amounts of slow growth above 0°C, and becomes ductile around 30°C.
64 citations
TL;DR: In this article, a bi-modal fracture analysis of polypropylene and nylon was performed in the temperature range −180 to −10° C and −160 to 20° C, respectively.
Abstract: Brittle fractures in polypropylene and nylon were obtained in the temperature range −180 to −10° C and −160 to 20° C, respectively. The fracture toughness results of surface notches and single edge notches showed a remarkable thickness dependence. This effect was explained in terms of a plane strain (K
C1) and a plane stress (K
C2) toughness value using a bi-modal fracture analysis. While K
C1 in both materials was generally insensitive to temperature, K
C1 was temperature dependent showing substantial viscoelastic effects. In polypropylene, the linear relationship between K
C2 and temperature (7”) was associated with the β and γ processes over the same temperature range. In nylon, there was a one-to-one correspondence between the K
C2 changes and the tan δ peaks due to the β and γ relaxation processes. Using a modified crack tip opening displacement (u) equation, i.e. u = ((KC2 − K
C1 )/σ
y
)2ey, where σ
y and ey are the yield stress and yield strain respectively, a constant u criterion was found to describe the fracture behaviour of both materials in the temperature ranges of the β and γ processes.
50 citations