Abstract:The concepts of damage effective stress and damage equivalence hypothesis play an important role in the development of continuum damage mechanics. Based on a generalization of the damage equivalence hypothesis, the so-called damage isotropy principle, it is found that the effective stress as a second-order tensor-valued function of the usual stress tensor and the damage tensor(s) has to be isotropic. Particularly, this property is regardless of the initial material symmetry (isotropy or anisotropy) and the typ… Show more
“…Several effective stress concepts in tensorial forms have been discussed by Betten et al [7,37] in more detail. Rewriting Equation (30) we obtain the damage variable…”
Section: Damage Evolution and Lifetime Estimationmentioning
In civil and mechanical engineering, the monitoring of structures is still a frequently investigated research topic. The basis of the present monitoring concept is the analysis of non-destructive measurements taken at regular time intervals to provide information about the current state of damage in a structure. The approach includes two steps: First, a data-driven stochastic subspace identification is applied to obtain a mathematical description of the system. Using a special state-space transformation, we transfer this result into physically meaningful system properties. Thereby the modal information can be separated into a part which describes the undamped system response and a second contribution which represents the influence of the damping. In the second step, we discretise the experimental setup by means of finite elements and apply an iterative finite element model updating algorithm to localise and to determine the damage. One important innovative aspect of the contribution lies in the updating of an entire damage evolution in order to estimate the lifetime of the structure. The experimental laboratory setup is based on a cantilever beam which is damaged locally and progressively with the help of a special device.
“…Several effective stress concepts in tensorial forms have been discussed by Betten et al [7,37] in more detail. Rewriting Equation (30) we obtain the damage variable…”
Section: Damage Evolution and Lifetime Estimationmentioning
In civil and mechanical engineering, the monitoring of structures is still a frequently investigated research topic. The basis of the present monitoring concept is the analysis of non-destructive measurements taken at regular time intervals to provide information about the current state of damage in a structure. The approach includes two steps: First, a data-driven stochastic subspace identification is applied to obtain a mathematical description of the system. Using a special state-space transformation, we transfer this result into physically meaningful system properties. Thereby the modal information can be separated into a part which describes the undamped system response and a second contribution which represents the influence of the damping. In the second step, we discretise the experimental setup by means of finite elements and apply an iterative finite element model updating algorithm to localise and to determine the damage. One important innovative aspect of the contribution lies in the updating of an entire damage evolution in order to estimate the lifetime of the structure. The experimental laboratory setup is based on a cantilever beam which is damaged locally and progressively with the help of a special device.
“…The description of material damage is based on the concept of effective stress [22][23][24]. Various proposals can be found in the literature regarding the formulation of a symmetrical effective stress tensor linked to a second-order damage tensor.…”
Section: Law Of Induced Anisotropic Damagementioning
SUMMARYThis paper presents a new constitutive model for the time dependent mechanical behaviour of rock which takes into account both viscoplastic behaviour and evolution of damage with respect to time. This model is built by associating a viscoplastic constitutive law to the damage theory. The main characteristics of this model are the account of a viscoplastic volumetric strain (i.e. contractancy and dilatancy) as well as the anisotropy of damage. The latter is described by a second rank tensor. Using this model, it is possible to predict delayed rupture by determining time to failure, in creep tests for example. The identification of the model parameters is based on experiments such as creep tests, relaxation tests and quasi-static tests. The physical meaning of these parameters is discussed and comparisons with lab tests are presented. The ability of the model to reproduce the delayed failure observed in tertiary creep is demonstrated as well as the sensitivity of the mechanical response to the rate of loading. The model could be used to simulate the evolution of the excavated damage zone around underground openings.
“…Fatigue damage COFFIN (1954) CHABOCHE (1974 DUFAILLY and LEMAITRE (1995) KRAJCINOVIC (1996) LEMAITRE (1992 LEMAITRE and CHABOCHE (1990) MANSON (1979) NAJAR (1994) SKOCZEN (1996) BETTEN (1983b) CHABOCHE (1981 H. ALTENBACH et al (1990;1997) HAYHURST and LECKIE (1973) HAYHURST et al(1984) J. KACHANOV (1958) KOWALESKI (1996a,b,c) KRAJCINOVIC (19831996) LECKIE andHAYHURST (1974) MURAKAMI (1983) NAUMENKO (1996) NEEDLEMAN et al (1995) QI (1998 QI and BERTRAM (1997) RABOTNOV (1969) STIGH (1985 TRAMPCZYNSKI et al (1981) ZHENG and BETTEN (1996) Nucleation and growth of microscopic transgranular cracks in the vicinity of surface. High cycle fatigue (number of cycles to failure larger than 10 5 ): effect of macroscopic plastic strain is negligible.…”
Section: Microscopic Mechanisms and Characteristic Featuresmentioning
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