Cracking tests, description

Using equipment shown in Techniace TC description, the critical strain for several chemicals was measured. Data are included in Table 3. It is evident that the chemical resistance of alloy is better than that of high impact ABS. Also, the cracking test by brake fluid was performed using method shown in Figure 2. After molded part was tapped, the brake fluid was poured to the whole tapped part and the occurrence of cracking at room temperature was examined. The results are included in Table 4. 

Descriptions of craze thickening are based on the observed crazes at the tip of a stationary crack for creep tests [29,30] and on observations of crazes in thin films by transmission electron microscopy (TEM) or small-angle X-ray scattering (SAXS) [31,32],... 

Keff is always higher than Kimax- In the ductile range, Kjmax/Keff 0.70 0.03 for both grades whatever the test conditions. In case of unstable crack propagation, Kimax Ketr The values of Ken(iPP/EPR-l)/KeH(iPP/EPR-2) for given test conditions are close to those of Kimax(iPP/EPR-l)/Kimax(iPP/EPR-2) when both grades exhibit the same macroscopic behaviour. In other words, Kimax is a semi-quantitative toughness parameter, whereas Kefr provides a quantitative description of the fracture resistance. 

Linear elastic fracture mechanics (LEFM) describes the behaviour of sharp cracks in linear, perfectly elastic materials. Since polymers are neither linear nor elastic, the utility of the theory may, at first sight, seem doubtful. In fact, the deviations from the theoretical assumptions are such that quite minor modifications to the analysis produce a precise description of crack growth in polymers within the framework of the conventional theory. The considerable resources of the subject may thus be utilised in that testing experience on other materials may be employed, together with the available analytical work. 

The paper is outlined as follows. After a brief description of the specimen preparation and the stress measurement by OFS, crack and spallation patterns on oxidised NiAl specimens are shown, which have been produced by bend and indentation tests at room or oxidation temperature. In the second part of the paper, first attempts to an interpretation of the crack patterns are presented. In particular, the possibility to derive the oxide fracture toughness and tensile strength from the crack patterns is discussed. 

Quantitative methods in AET rely on localization techniques to determine the coordinates of the emission souree, to image cracks in the material. The method used to localize AE events depends on the geometry of the object being tested, and whether the resolution is required in one, two or three dimensions. Although a detailed description of these methods is the focus of Chap. 6, basic concepts - in particular using full waveforms - are described in this chapter for completion and to understand signal-based procedures. 

ABSTRACT To identify the relationship between the development of surface discontinuities and the stress-strain state of rocks, we introduce a paper, which is based on laboratory experiments. Artificial (a mixture of cement and sand) and natural rock specimens (marble, dolerite, sandstone) were made in the form of disks with thickness of 10 mm and diameter of 30 mm. Mechanical Brazilian tests were performed by servo-hydraulic press Instron 8802. The crack propagation during the mechanical tests was recorded with industrial camera Pixelink. The plots identifying stages of loading and depending on the behavior of the summed surface deformation pattern of the fracture were drawn. Study allowed to get a more detailed description of rock deformation and prediction of discontinuities (cracks) formation through the observed surface deformations. 

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