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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decreasing deficiency or increasing efficiency of dissipated strain energy for fracture damage formation with initial damage. It seems so that with increasing initial damage an increasing portion of the total dissipated energy is spent on micro-crack formation or/and new surface opening processes taking place around initial damaging defects. In particular, this behavior is more pronounced in the case of hole initial damage for which, as shown in Fig.7, an overall shift of the related curve to higher values occurs. This behavior is consisted with the earlier explanations concerning the influence of initial hole damage where holes as “mild” energy sinks, allow enough time for energy dissipation for development of new microdamage sites within the virgin material.

Initia l hole-damage Initia l common edge-crack damage Slanted edge-crack damage

Initia l hole-damage Initia l common edge-crack damage Slanted edge-crack damage

1.2

12

0.8

8

I θ f /II θ f

ω θ f ω f -1

0.4

4

0

0

0

0.2

0.4

0.6

0

0.2

0.4

0.6

D 0

D 0

Fig. 6. Evolution of failure strain energy efficiency number with initial damage D 0 .

Fig.7. Evolution of energy dissipation of damage formation deficiency (efficiency) number with initial damage D0

4. Conclusions

In this work two main types of initial damage of the materials were investigated. In particular the authors examined the edge-crack and hole- formed damage. In this framework, under the given circumstances of theoretical and expe rimental factors, the present study has shown that the initial damage may markedly influence the investigated fractural damage parameters as follows:  The damage at failure attains larger values with hole initial damage than with edge-crack initial damage.  Structural instability number shows a monotonic increase with both types of initial damage.  Failure strain energy efficiency number shows a higher rate of change with microhole initial damage than with edge-crack initial damage.  The damage process intensity number decreases rapidly linearly with edge - crack initial damage whereas slowly and non linearly with hole initial damage.  Strain energy dissipation deficiency (efficiency) number decrease(increase) monotonic with initial damage. This behavior is more pronounced in the case of initial hole damage. In closing, it can be stated that, all the investigated damage parameters, showed a greater fracture sensitivity with initial hole damage, than those with edge-crack initial damage.

References

Budiansky, B., O’Connell, R.J., 1976. Elastic moduli of a cracked solid. International Journal of Solids and Structures 12, 81-97 . Basaran, C., Nie, S., 2004. An irreversible thermodynamics theory for damage mechanics of solids. International Journal of Damage Mechanics 13(3), 205-223. Gyarmati, I., 1970. Non-equilibrium Thermodynamics, Field Theory and Variational Principles, Springer Verlag. Hult, J., 1975. Damage-Induced Tensile Instability. Netherlands: North-Holland.