单轴拉伸试验砖的实验研究t.docVIP

Experimental Investigation of Bricks Under Uniaxial Tensile Testing BSTRACT Softening is a gradual decrease of mechanical resistanceresulting from a continuous increase of deformation imposedon a material specimen or structure. It is a salient feature ofquasi-brittlematerials like clay brick, mortar, ceramics, stoneor concrete which fail due to a process of progressiveInternal crack growth. Such mechanical behaviour iscommonly attributed to the heterogeneity of the material,due to the presence of different phases and materialdefects, such as flaws and voids. For tensile failure thisphenomenon has been well identified for concrete but veryfew results exists for clay brick.. In the present paper, theresults of an extensive set of tests carried out at Universityof Minho and including three different types of back underniaxial tension will be presented. Both tensile strength andfracture energy are quantified, with recommendations for theadoption of practical values. INTRODUCTION The tensile behaviour of concrete and other quasi-brittlematerials that have a disordered Internal structure, such asbrick. can be well described by the cohesive crack modelproposed initially by HILLERBORG [1]. This model has beenwidely used as the fundamental model that describes thenon-linear fracture mechanics of quasi-brittle materials, e.g.[2,3]. According to this model and due to crackinglocalization, which is a characteristic of fracture process Inquasi-brittle materials, the tensile behaviour Is characterizedby two constitutive laws associated with different zones ofthe material during the loading process.see Figure 1. Theelastic-plastic stress-strain relationship of Figure la is validuntil the peak load is reached. It is noted that before thepeak Inelastic behaviour occurs due to micro-cracking andthe energy dissipated in this process is usually neglected forthe calculation of the fracture energy. The stress-crackopening displacement relationship of Figure lb describesthe strain soften