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Abstract Based on the mesoscopic heterogeneous characteristics of materials，a two-layered numerical model is simulated to study the stress distribution，fracture propagation and the mechanism of edge fracturing due to shrinkage from even cooling of overall upper layer or cooling temperature passing down over time in two-layered materials. Firstly，the stress state between two adjacent fractures of the model subjected to even cooling with a fractured surface is studied；and the stress in the center between the two fractures is the maximum，with the fracture spacing decreaseing， decreases continuously and the stress state changes from tensile to compression，the critical spacing to layer thickness ratio is approximately 3.0 when fracture saturates. Secondly，two-layered model without pre-existing fractures subjected to two types of temperature loading is studied；one with upper layer temperature cooled evenly to －40 ℃ and the other with surface temperature cooled to －35 ℃ rapidly(temperature shock). The results show that the fracture formations due to the two conditions are in a common mode：the first fracture insertes into the middle of upper layer，new fractures inserte into the middle of existing fractures or fracture to the ends until fracture saturation，rather differences are that in the overall even cooling model fractures initiate not only from the surface，but also from the middle，the temperature shock fractures extend always from surface to inside，and with a larger number. This study reproduced the following three stages under cooling shrinkage：micro-fracture initiation，fracture propagation，and fracture saturation；it also shows the process of heat conduction under thermal shock，by comparing results under two temperatures conditions. Finally，the paper introduces that using material with better temperature conductivity would help to reduce surface fractures in road structure.
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Received: 03 May 2013
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2014, Vol. 33 
