Plastics quasi-static testing

When an atmospheric spray specimen was subjected to a quasi-static test with an indenter of 1 mmcj), both the substrate and the bond coat were affected with marked plastic deformation, and in particular, the substrate underwent so drastically that the limit of elastic-plastic deformation was stepped over to present a porous zone with concentrated cracks. As the indenter size grew, the area of plastic deformation in the substrate and the bond coat was reduced, to present Hertz cone cracks in the cross-section. In addition to Hertz cone cracks, a number of cracks were seen in parallel to the substrate, which were thought to have occurred when the load was eliminated. With an indenter of 4 mmcj), the area of plastic deformation was reduced further, and lateral cracks were observed as the load was eliminated. Debonding between the bond coat and the substrate was observed only with the 4-mm indenter. Comparing to impact tests results(Fig. 7), qusi-static tests(Fig. 14) can reproduce similar fracture behavior. 

A summary of quasi-static delamination test methods for continuous-fibre, unidirectional FRP composites is given in Table 8.1. For mode 1, several standard test methods exist, namely, JIS K7086 ( Testing methods for interlaminar fracture toughness of carbon fibre reinforced plastics , 1993) this also includes a quasi-static mode 11 standard test, ASTM... 

The compression properties characterize the strength, deformation and stiffness behaviour of plastics under quasi-static uniaxial compression load conditions. Generally, for these tests commercial universal test systems with different load capacity are used. The valid and common used standard for the compression test of plastics is the ISO 604 (2002) Plastics - Determination of compressive properties. The data collected include also values determined according DIN 53454 and DIN 53457 as well as ASTM D 695 (Fig. 4.33). The specimen of preference exhibits dimensions of 50 x 10x4 mm for the determination of modulus of elasticity and 10 x 10x4 mm for the investigation of the other compressive properties (Fig. 4.34). 

Figure 3 shows the load (P) - load line displacement (5) records obtained from fracture tests at room temperature and at quasi-static conditions (low loading rates) of propylene homopolymer, PPO, and thee controlled-rheology PPs. The mechanical response for all the materials presented clearly elastic-plastic behaviour and this justifies the use of the EPFM multiple specimen method to evaluate the fracture behaviour. In addition, all the curves deviated from linearity and at a certain deflection level, sudden instability occurred and the specimen broke in two halves. The difference in stiffness is due to the different initial crack lengths. 

For the splitting of the quasi-static stress - obtained after the substraction of (Tr from the measured stress a - into its two components, the asymptotic behavior at large strains can be used. It is dominated by the network forces and thus determined by the associated network shear modulus. The properties of the crystallite branch, i.e., the associated elasticity and finite plasticity, follow from step-cycle tests. 

The first protocol completed was the test method for determining the critical stress intensity factor, Kjc, and fiacture energy, Gic, in plastics under conditions of dow ( quasi-static ) loading [2], This test method has been found to be reasonably successful and it has been adopted as a standard by ASIM (Test Methods for Plane-Strain Fracture Toughness and Stixun Energy Release Rate of Plastic Materials, D 5045-93) and is currently under consideration by ISO [3]. 

The procedure to calculate fiber orientation is the same as explained above, but their implementation into explicit solvers and non-linear material models is more complex than it is for quasi-static load-cases and purely elastic material models. The fiber orientation is characterized by a so called orientation distribution function (ODE) that describes the chance of a fiber being oriented into a certain direction. For isotropic, elastic matrix materials an integral of the individual stiffness in every possible direction weighted with the ODE provides the complete information about the anisotropic stiffness of the compound. However, this integral can not be solved in case of plastic deformation as needed for crash-simulation. Therefore it is necessary to approximate and reconstruct the full information of the ODE by a sum of finite, discrete directions with their stiffness, so called grains [10]. Currently these grains are implemented into a material description and different methods of formulation are tested. 

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