Quasi-indentation test

Figure 2. An overall view of quasi static indentation testing system.

With specimens prepared in different ways, the results of quasi-static testing using spherical indenters of different diameters and those of fracture observation after impact tests using 1 mmcf) spherical particle were compared. 

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. 

Before the impact test, quasi-static indentation tests were performed on the same machine (MTS 810), as shown in Figure 19.2, to investigate the strain-rate effect and perforation energy of the proposed composite laminates. 

Fignre 19 J Comparison of reaction force—displacement curves under a quasi-static indentation test. 

Similar to quasi-static indentation tests, the effect of 1 wt% NC and 1 wt% GB fillers on the impact response of GFRP was initially investigated. Figure 19.13 shows representative force—time curves for each material configuration. As seen in Figure 19.13,... 

In quasi-indentation and impact tests, the 1 wt% NC-modilied laminate exhibited the lowest first damage set point and stiffness. 

In general, taking into consideration the experimental quasi-static indentation and low-velocity impact test data, the results found and their correlations with damage observations could provide valuable information for better design of innovative lightweight vehicle components made of composite materials. In addition, filler materials, such as GBs, could play a significant role in improving the crashworthiness and occupant safety in the event of a vehicle crash. 

The objective of the current work was to compare FOD behavior between the SiC/SiC and the oxide/oxide CMCs in terms of impact morphologies and strength degradation, based on the previous work [1-2], In addition, the response to static indentation of the two composites with respect to deformation was also characterized using the same steel balls that were employed in the previous FOD testing. The static indentation results were then used in order to make an attempt of quasi-static prediction of impact force as a function of impact velocity involved in the FOD testing. 

Since polymers are viscoelastic materials it is necessaiy to specify both the temperature and the time scale under which the result was obtained. This protocol is meant for low speed ( quasi-static ) displacement contrd mode of loading and as a bade test condition, it is recommended that 23°C and a load-point displacement rate of 10 mm/min be used, but other conditions are possible. Li all cases, the time-D-ffacture should be quoted and all related determinations (yield stress and indentation correction, see below) should be obtained at comparable loading times as for the fracture test... 

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