Impact stress field

For many applications, the toughness of sPS is insufficient, which has thus led to many attempts in the past to increase its toughness significantly compared with HIPS by blending with rubbers. In the stress field of softer or harder particles than the sPS matrix, typical deformation processes inherent to the matrix are initiated. For rubber modification it is important that the application or test temperature is above the glass transition temperature of the rubber, otherwise the stiffnesses of the two components hardly differ from each other and local stress fields around the rubber particles are not formed. The formation of numerous deformation zones round the rubber particles is generally the basis of impact modification [10]. 

It is noted that attempts to apply composites theory to the materials investigated have not been entirely successful. While upper and lower bounds on, e g., moduli can be established there is little quantitative ediction of the impact strei th or fracture toughness parameters of the composites. Hence, the systems cannot be considered as optimized, for example, with regard to impact strength versus particle size, shape, or distribution or matrix-particle adhesion. The complexity is, of course, due to the statistical structure of the dispersed phase and the resultant uncertainties in the calculations of local stress fields, which in turn imply uncertainty in the local mode of yielding or rate of yielding. 

Chen, G.X., Dou, L.M., Qian, Z.D., 2008. The Stress Field Distribution in Folding Structure Areas and Its Impaction on Rock Burst. Journal of China University of Mining Technology 37(6) 751-755. 

As shown in Figure 10, the in-situ stresses field is influenced by the faults obviously, especially for the F14 faults, and the stress is concentrated in the fault zone and will be impact on the stability of surrounding rock mass after excavation. 

High temperature. The rubber is able to relax even in the rapidly forming stress field ahead of the travelling crack. Stress whitening occurs over the whole of the fracture surface. Bucknall and Smith [128] report similar results for other rubber-modified impact polymers. 

The base area, in addition to being susceptible to impact failure, can fail catastrophically from environmental stress cracking. Such cracking is a function of exposure to chemicals, which attack the plastics, and a biaxial stress field, which exists in the base. For PET, the main concerns are soaps used on filling line conveyors for cleaning and line lubrication, generally known as line lubes, and the hardness-alkalinity of the water. It is therefore important to thin out the wall in the base in the shortest possible distance from the center and build-up as much orientation as possible in this area. The specified base clearance must take into account that it is reduced from the molded dimension due to deformation and bottle creep under the carbonation pressure. 

The Izod test has a potential disadvantage in that the test piece is clamped which can result in a stress field in the vicinity of the notch prior to impact. On the other hand, the Charpy test consists of a simply supported beam which is not stressed prior to impact. 

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