Double-edge notched specimen

Tnucleation is less effective with a low molecular grade than with a high molecular one. The temperatures at which the ductile-brittle transitions, Tdb, occur for selected non-nucleated and -nucleated sets support our conclusion (Fig. 5) /J-nucleation lowers the Tdb by about 50 °C independently of the flowabihty of the neat polymer. Although these tests were performed with single notched specimens, they can be correlated to a certain extent to those carried out on double-edge notched specimens. Sect. 3.2.4 deals in more detail with the influence of the local stress concentration on the mechanical responses of P-iPP. 

In order to investigate the deformation mechanisms operating under impact, double edge-notched specimens were subjected to impact loading in three-point bend geometry (8-10). The plastic zones formed around cracks grown subcritically in this way were sampled at different points by ultramicro-toming sections for examination by TEM. 

To investigate the temperature dependence, we equipped the tensile tester with an environmental chamber where the temperature was controlled within 0.1 °C. Double-edge-notched specimens with a gauge length of 2mm were employed because of the limited size of the chamber. 

DENT double edge notch tensile specimen... 

Fig. 3 Evolution of the double edge-notched impact strength, dNIS, with the logarithm of the melt flow rate, MFR, a at room temperature and b - 20 °C. The test speed was about 3.8 ms4, the specimens were injection molded...

Figure 9. TEM images of stained sections showing deformation in the vicinity of a crack subcritically grown under impact in a double edge-notched, three-point bend specimen of 3LE31 (a) low-magnification micrograph showing the presence of planar deformation zones adjacent to the crack and (b) the zones in (a) shown at a higher magnification.

The alternative specimens are center notched (CN). double-edge notched (DEN) and single-edge notched (SEN) tensile specimens. Unlike DCB tests, these tests produce a single load-slow crack growth. The formulae used to compute are [195] ... 

DENT double-edge-notched tension specimen... 

Fig. 20. (a) Double-edge notched tension (DENT) specimen and indication where the essential (We) and the nonessential work of fracture (Wp) is dissipated, (b) schematic EWF plot. 

Fracture toughness R was evaluated from tensile tests performed on double-edge notched (DEN) specimens by determining the specific essential work of fracture under limiting conditions of the length of the ligament being equal to zero (Martins et al., 2009). 

Polymer pellets of isotactic polypropylene (iPP) were melted in a laboratory hot press for 15 min at 230 °C and 10 MPa, and then quenched in ice water (0 °C) or boiling water (100 °C). To control the crystallinity of the iPP sample, we annealed the sample sheets prepared at 0 °C for 2 hr at various temperatures from 40 to 140 °C. Square pillar shaped test specimens were cut out from a 1 mm thick sheet and used for the measurements. Double-edge notched sample specimens with the gauge length of 2 mm were used for the temperature dependence and the dumbbell shaped specimen with gauge length of 5 mm for the elongation speed dependence. 

The measurements are carried out on deeply notched specimens, either single-edge-notched tension (SENT) or double-edge-notched tension (DENT) (see Figure 13.22). The total work of fracture Wf consists of two components. First, there is the work expended in the inner zone We, which is called the essential work of fracture. This relates directly to the energy required to fracture the sample and is therefore proportional to the ligament... 

FIG. 37 Dependence of impact strength of UHMWPE at 23°C notched (curve 1) and double-edge notched (curve 2) specimens on melt flow index. (From Ref. 25.)... 

Evaluation of fracture toughness was studied by means of essential work of fracture (EWF), using Inun thickness injection moulded double-edge notched tensile (DENT) specimens with two types of materials, ABS and PP. Stress level analysis is discussed in this paper by means of maximum nominal stfess. 

A round robin test result was reported and discussed in the previous paper [5] using double edge notched tensile (DENT) specimens of 1mm thickness injection moulded plastics with two types of materials ABS as a semi-ductile material and PP as a ductile material, aiming at investigation of the cause of lab dependency of this method or to find possibility of improvement in reproducibility. These injection moulded specimens were... 

The Essential Work of Fracture (EWF) technique is a valuable tool to determine the fracture behavior of ductile materials such as polyethylenes under plane stress conditions. [1-3]. The method is based on simple tensile tests performed to DDENT (deeply double-edge notched in tension) specimens. The plastic zone generated at the crack tip during the fracture process can be divided in two regions an inner fracture process zone (IFPZ or FPZ), where fracture surfaces are formed, and a surrounding zone called outer process zone (OPT), where the large plastic deformation exhibited by the material is distributed. 

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