Narrow Results

We study crack patterns in laponite films of different thickness. The patterns show a self-similarity under coarse-graining, the fractal dimension determined by box-counting has a value around 1.66, independent of film thickness. The cracks on layers of different thickness show a remarkable scaling bahavior. We have measured the cumulative area covered by the cracks versus minimum crack-width resolved. Curves representing crack area for different thickness collapse onto a single curve, when the crack widths are scaled by the film thickness.

Peridynamics (PDs) is a nonlocal continuum mechanics theory used to solve fracture and failure problems. The classical bond-based peridynamics (BBPDs) involves one parameter to describe the microelastic bond stretch response, which makes the Poisson’s ratio restricted. In previous studies, kinds of extended bond-based peridynamic (EBBPD) models were proposed to deal with the limitation of Poisson’s ratio in BBPDs. In this paper, four benchmarks with different load conditions are designed to compare the performance of five EBBPD models and to investigate the effects of model parameters on crack propagation. Results show that compared with BBPDs, the crack patterns of the EBBPD models have the main form of BBPDs; on the other hand, the introduction of tangential stiffness makes the form of crack tend to shear failure, and the increase of tangential stiffness will enhance this effect. The crack patterns transition of wing cracks from tensile failure to mixed tensile–shear failure when the tangential stiffness increases. For the models with rotational stiffness, the rotational stiffness affects the width and propagation direction of the secondary crack and makes the trends to shear failure. Besides, the rotational stiffness affects the forms of crack coalescence and divides the results of these five models into three types.

This paper presents test results of mechanical behavior, failure pattern and b-value of full-scale flat-plate floor subjected to fire. The experimental results show that crack patterns on top surface of the flat-plate floor under fire are consistent with those at ambient temperature. The experimental results also show that concrete spalling has a significant impact on fire resistance of the flat-plate floor. Serious spalling would directly cause failure of concrete structures or members under fire even though they have not reached their fire resistance. On the basis of experimental results, acoustic emission parameters were analysed, which proved that b-value has a close relationship with the damage variation rate of the slab and can be used to estimate the damage process of the flat-plate floor under fire.