PSI - Issue 10

V.N. Kytopoulos et al. / Procedia Structural Integrity 10 (2018) 272–279 V. N. Kytopoulos e al. / Structural Integrity Procedia 00 (2018) 000 – 000

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3

Finally, an additional basic primary parameter is the dimensionless dissipation energy at failure ω θ f , which consists of two components I θ f and II θ f . The first one corresponds to the heat-convertible energy whereas the second one to damage-related surface opening or interface separation energy. By using the principle of the minimum dissipation energy the two components can be calculated by the following particular equations Lemaitre (1996), Hult (1975):

f D         0 f D

I

D ln

D D



(3)

θf

f

0

f D D     1 1 0

II

(4)

θf

For the needs of the present work, besides the three basic primary parameters, K , D 0 and D f certain additional variant ones is proposed to be used: ω φ -1 , ω θ f ω φ -1 and I θf / II θf . 3. Experimental details The tensile loading experiments were carried out by taking into consideration the basic assumptions of continuum damage mechanics, which allow analysis of brittle damage to be applied to elastic-brittle solids under low dynamic loading conditions (Krajcinovic et al. (1987); Lemaitre (1996)). Under these circumstances, a polymeric material, under the commercial name PMMA (Plexiglas) was selected, which has shown to fulfill, to a satisfactory manner, most of the desired assumptions. The specimens have a dog bone geometry with given initial damage as shown in Figs.1(a,b). The initial damage was defined and simulated on the basis of a decreasing load carrying area principle.

(a) (b) Fig. 1. Specimen geometry with (a) increasing initial hole damage and (b) with perpendicular and slant initial double edge-crack damage. In this sense two main types of initial damage were examined: Hole-formed damage and double edge-crack-formed damage as shown in Fig.1. The holes were prepared by machining drilling to present a diameter of 1 mm whereas edge-cracks were introduced by a rotating diamond disc cutting process. The thickness of the cutting disc was 0.1 mm, which reflects the width of the edge-crack (notch). The slow cutting process allows a minimum of “unintentional” notch damage to be introduced in the material. In particular, one can demonstrate on the example of hole-simulated damage that the maximum initial damage tends to a maximum limiting value close to the theoretical one (i.e., 0.49). In Fig.2 an optimum geometrical arrange ment of equidistant holes is presented, where W is the width of specimen, d ≤ s the diameter of the holes and s the distance between them . Now by the condition s=d, the minimum distance between “discontinuities” i.e. , between holes