Tomasz Garbowski

MECHANICAL CHARACTERIZATION OF MATERIALS AND DIAGNOSIS OF STRUCTURES BY INVERSE ANALYSES: SOME INNOVATIVE PROCEDURES AND APPLICATIONS

A survey is presented herein of some recent research contributions to the methodology of inverse structural analysis based on statical tests for diagnosis of possibly damaged structures and for mechanical characterization of materials in diverse industrial environments. The following issues are briefly considered: identifications of parameters in material models and of residual stresses on the basis of indentation experiments; mechanical characterization of free-foils and laminates by cruciform and compression tests and digital image correlation measurements; diagnosis, both superficially and in depth, of concrete dams, possibly affected by alkali-silica-reaction or otherwise damaged.

Multi-level backcalculation algorithm for robust determination of pavement layers parameters

The backcalculation procedure applied to a mechanical characterization of the road pavement is usually limited to an identification of the elastic modulus of each layer only. The remaining parameters of the model are usually set as known, while performing an inverse analysis. Among assumed parameters are thicknesses of the model layers and frequently considered as constants on a homogeneous section of the road. This is an obvious simplification, because sections in general are inhomogeneous, i.e. the thickness of each layer changes slightly along each road section. Thus the precise and possibly nondestructive estimation of the layers thicknesses is very important and crucial in the inverse procedure. Here, a hybrid form of the optimization algorithm, where the condition of a constant thickness does not need to be fulfilled is described. Further on, the objective function is formed as a discrepancy between reference and computed deflection derivative instead of a deflection curve. In consequence, the values of backcalculated parameters are several per cent more precise compared to a standard procedure. Whenever the thickness of the asphalt layer of the pavement structure cannot be assumed a priori as a constant, the proposed here method appears to be necessary if one does not want to perform costly and destructive in situ drilling tests.

Materials Mechanical Characterizations and Structural Diagnoses by Inverse Analyses

Mechanical damages in structures, in structural components of plants and in industrial products usually imply changes of parameters which have central roles in computational modelling apt to assess safety margins with respect to service loading. Such parameters may depend also on the production processes in industrial environments. In this chapter, the parameter identification methodology by inverse analyses is dealt with under the following limitations: experiments at macroscale level, deterministic approaches, statical external actions and time independence in material behaviours. Semiempirical approaches frequently adopted in codes of practice are not dealt with here. The inverse analysis methods outlined here are centered on computational simulations of tests (namely, direct analyses), sensitivity analyses for the optimal design of experiments, model reduction procedures and other provisions apt to make fast and economical the parameter estimation in engineering practice. The applications summarized here as examples concern structural diagnoses based on indentation tests, in situ diagnostic experiments on concrete dams and laboratory mechanical characterization of membranes and laminates. Introductory Remarks The “inverse analysis”methodology is an area of applied sciences which at present is still growing as for improvements of procedures and as for variety of engineering applications. Inverse analysis is based on information concerning the response of a “system” to external actions and leads to the identification of some features of the system, usually parameters included in its modelling and, hence, in the computer simulation of the system response to those actions. In the present context of applied mechanics, the features to assess are usually either parameters contained in material constitutive models or stresses present in the system and included in the set of “parameters” to estimate or “identify.” The system may be a laboratory specimen or a structural component as industrial product; however, frequently, it consists of a structure possibly affected by damages due to deterioration in service. Therefore, inverse analysis is becoming central to “structural diagnosis” intended to provide a reliable basis for the subsequent “direct analyses” apt to assess “margins of safety” with respect to collapses or to substantial further structural damages (“admissible stress” criteria being superseded now in more and more industrial codes). *Email: giulio.maier@polimi.it Handbook of Damage Mechanics DOI 10.1007/978-1-4614-8968-9_33-1 # Springer Science+Business Media New York 2013