Local stress test

Fig. 2. Schematic of energy dissipation in a commonly used peel test. The energy dissipation can occur in the adhesive and/or the adherends. The extent of energy dissipation depends on the elasto-plastic properties of the adhesive and the adherends under the test conditions as well as the local stresses and strains near the crack tip.

E. W. Hart, Stable Crack Extension Rates in Ductile Materials Characterization by a Local Stress-Intensity Factor, in Elastic-Plastic Fracture Second Symposium, Volume I—Inelastic Crack Analysis, eds. C. F. Shih and J. P. Gudas, ASTM STP 803, American Society for Testing and Materials, Philadelphia, PA, 1983, pp. I-521-I-531. 

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. 

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]. 

In comparing the shear fracture surfaces of amorphous and semi-crystalline polymers, it appears that the features in both cases are quite similar (Fig. 39a -c ). This indicates that, under comparable conditions, the local stress field rather than details of the crystalline-amorphous microstructure of the polymers tested determines the operating deformation mechanism. Only secondary effects arise from the morphology of the cry stalline material. 

Notch Effect - The effect of the presence of specimen notch or its geometry on the outcome of a test such as an impact strength test of plastics. Notching results in local stresses and accelerates failure in both static and cycling testing (mechanical, ozone cracking, etc ). 

The hazard of brittle-fracture is lessened as the average and local stress levels are lowered. Both the ASME Unfired Pressure Vessel Code (Par. UCS-66) and the Code for Pressure Piping (Par. 323.2.2) recognize this by allowing materials to be used below the transition temperature. Where the allowable stress is reduced to 40% of the normal allowable, the ASME Code permits such material to be used without limitation. The code for pressure piping sets an allowable stress of 15% of the maximum allowable without impact test. 

To study hydromechanical coupling in deep stiff clays we need to supply mean stress relatively high linked to the in situ stress state. Thus, to perform triaxial tests on stiff clays with permeability measurement we use a special triaxial apparatus (high pressure cell) with two independent drainage line. We have developed also a system for local strain measurements composed of 7 LVDTs which are suitable for tests in oil (confining fluid) under high level of stress. Tests are performed on cylindrical specimens (up to 80 mm in height and 40 mm in diameter). 

In a local detailed analysis, the flexible adhesive is modeled with three-dimensional solid elements to enable the refined capture of any local stress or strain gradients. The adhesive material is described as a rabber-like, nearly incompressible, hyperelastic material characterized by a strain energy function. Using U as the strain energy potential per unit of the reference volume, the form of the Ogden strain energy potential is shown in Eq. (1) jii and u are material parameters which are determined from adhesive material test data. 

The lap shear fatigue test for the joints of the front cab module of the Maglev Transrapid TR08 has been analyzed by a fine detail analysis with 3D solid elements using the real cross-section geometry. The adherend materials are aluminum on one side and GRP on the other see also Section 32.5.1. The PU adhesive Sikaflex -254 Booster is modeled with the Ogden strain energy equation (Eq. (1), with N=2). The computed stiffness correlates well with the test results. The local stress distribution is visualized in Fig. 32.11. 

Stresses caused by external local loads are a major concern to designers of pressure vessels. The techniques for analyzing local stresses and the methods of handling these loadings to keep these stresses within prescribed limits has been the focus of much research. Various theories and techniques have been proposed and investigated by experimental testing to verify the accuracy of the solutions. 

Figure 2.9 Tensile test for one-ply composite Exfieriment experiments (3 representative samples) and FEA the simulalion results. The model has the following feamres o-FVF = 44%, iy-FVF = 74.5%, inter-yam matrix layer is 20 pm. The transverse strength is assumed to be 40 MPa, the longitudinal strength is 1280 MPa at 60% FVF. The local stress is used to predict...

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