Marcin Chrzanowski

A Non-Unilateral Damage in Creeping Plates

The effect of compressive stresses upon the creep failure of structures has been analysed in the paper. A combined theory of that by D.R. Hayhurst [1] and J. Lemaitre [2] was used to describe damage evolution, whereas a non-stationary creep theory coupled with damage described the structure deformation. Isochronous limit curves in plane stress state were build, and the clamped and simply supported plates were analysed to demonstrate the influence of compressive stresses.

On creep rupture of rectangular plates

The paper deals with the evaluation of life-time of creeping plates. In particular, the boundary conditions and effects of equivalent stress are studied. Both, the role of failure mechanism modes governed by maximum principal stress and effective stress, as well as the effect of compressive stress are evaluated. The analysis covers two periods of damage growth, i.e. that before first macrocrack appearance, and that which leads to failure in a characteristic cross-section of the plate.

Ductile creep rupture of fibre bundles

Abstract The time dependent rupture of linearly viscous ideal fibre bundles is analysed, considering the influence of locally varying fibre properties. Immediate and delayed rupture modes, which may be of instantaneous or gradual nature, are identified to occur depending upon the distribution of fibre properties. The existence of an incubation time is revealed as a consequence of the assumed fibre properties.

Safety of materials and structures in creep conditions

Abstract This paper deals with the evaluation of safety structures in creep conditions. It appears to be a function of applied load and operation time, and structural analysis has to take into account both residual strength reduction and time-dependent failure under constant load. The continuum damage mechanics that uses a new state variable associated with material deterioration was used in the analysis performed in this paper. First, attention was paid to residual strength reduction that occurs in any point of a structures body, then the analysis was enhanced to cover all stages of the failure process that can be distinguished when structural behaviour is taken into account. Two types of structures (trusses and plates) were chosen to demonstrate the influence of this effect upon life-time evaluation of structures.

Development of Non-unilateral Damage Field in Creeping Plates

Paper deals with damage development in plates made of materials which exhibit asymmetric behaviour with respect to its deterioration (different tension and compression failure). Material properties are assumed to be time dependent, and analysis is carried out within two time periods: in the first damage is nucleated till macrodefect appearance, and in the second one macrodefects are spreading until they span plate thickens. Ratio of these two time periods is considered as safety margin of analysed structure.

Ultrasonic Damage Measurement in Reinforced Concrete Beams

In several situations the failure of a reinforced concrete structure is preceded by a gradual deterioration of the materials which can be recognised by measuring the change of their physical properties [1]. The main purpose of the destructive tests described in the present paper was to obtain an evaluation of the damage evolution in a reinforced concrete beam, submitted to harmonic displacements imposed by means of a shaking table. A reinforced concrete beam, with two different spans, was designed to sustain a static load of a mass located at the centre of the longer span. Ten identical specimens were prepared and tested at the LNEC (National Laboratory for Civil Engineering, Lisbon) shaking table facility [2]. This paper presents tests, which have been performed in the frame of the European Commission programme ECOEST/PECO (European Consortium of Earthquake Shaking Tables / Central and Eastern European Countries extension). The beams were fixed to the shaking table and submitted to a sinusoidal displacement in the vertical direction, with a pre-established duration and constant amplitude. The tests were carried out by successive stages of increasing amplitudes, until the collapse of each beam was reached. The tests aimed to give an evaluation of the loading history influence on the occurrence of the critical state. During the tests, displacements and accelerations were continuously recorded at several points of the structures, along with ultrasonic measurements taken at different directions, before and after each successive stage. In the present paper the design of the specimens is given. The instrumentation plan, the test setup and the test procedure are also described. Finally, the most relevant results are shown followed by the formulation of a global damage law to predict the limit state of the beams.

Cracking of Creeping Structures Described by Means of CDM

Engineering design of a structure should sustain all loading history. Consequently, two aspects of structure’s usability are usually studied i.e. structure’s deformability and its integrity. The latter one is of prime importance for structure’s reliability.