13th International Conference on Fracture June 16–21, 2013, Beijing, China -3- Table 1 outlines the bottom line for a user when dynamic fracture mechanics tests have to be drafted. The first thing to note about Table 1 is that the recommendations of [1] and [2] regarding strain gage positions for force measurement are very different. This mirrors the status in the literature including for instance early basic studies of Ireland [4, 5] or Trudeau [6] which are still frequently cited. Some own experimental results will be discussed below. With respect to load line displacement measurement BS [1] does not provide a convenient method for higher loading rates. The recommendation to approximate the test machine ram displacement is rated not sufficient. Compared with this, ASTM [2] at least indicates that non-contact optical methods are suited and inertial effects shall be avoided. 2. Experiments The paper reports on experimental fracture mechanics impact investigations on bend type specimens of DCI materials. Depending on the DCI’s material behavior [7], two types of tests have been investigated: a small scale low blow multiple specimen technique using a drop tower was investigated for crack resistance curve determination as well as large scale full blow tests on SE(B)140 specimens were performed. Different experimental aspects of the test methods are discussed here. Mechanical properties, microstructural aspects and the values of the fracture mechanics characteristics of the materials are not in the focus of this paper. They will be reported elsewhere. 2.1. Small scale low blow tests When the DCI material exhibits R-curve behavior, it is still first choice to use the low blow multiple specimen technique for dynamic crack resistance curve determination. Unfortunately, single specimen techniques, as the key curve method, have not been proved successfully to be appropriate and to provide enough precision with DCI materials at dynamic loading conditions [8]. Primary goal of the investigations was to setup a multiple specimen test method to determine dynamic crack resistance curves in the temperature range from ambient to -40 °C. Series of small scale low blow tests on SE(B)25 specimens (length 138 mm, width 25 mm, thickness 25 mm, a0/W = 0.5) were performed by use of a drop tower test system (Fig. 1) at stress intensity rates in the linear-elastic range of approximately 3·105 MPa√ms-1. Figure 1. Left: BAM drop tower test system with v0max ≈ 8 ms -1, max. energy ≈ 300 J, right: test setup with SE(B)25-specimen instrumented for opto-electronic measurement of load line displacement.
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