بررسی نحوه ی گسترش ترک های بالا به پایین 1 در روسازی های آسفالتی، با استفاده از (TDC) فرضیه ی مکانیک شکست

Abstract
Fatigue can be expressed as the failure of asphalt concrete under repeated loading in such a way that
stress induced in the asphalt layer could be less than ultimate strength of the material. Fatigue cracking
in asphalt concrete layer can be classified into two types regarding the place of crack initiation and the
type of crack propagation. The first type the cracks initiated in the bottom of asphalt layer and
propagates upward. This type of cracking is produced in the thin asphalt layer. The second type of
cracking which is produced in thick asphalt layer is initiated in surface area then propagates downward
which is called Top-Down cracking. The second type of cracking is studied less compared to the first
one. One type of fatigue cracking, is fracture mechanics approach in which the failure in asphalt
mixture is related to number of repeated loading. In this study the fracture mechanics approach was
implemented to understand the effective parameters in propagation of top-down cracking. as well as
developing a model to interpret the crack propagation in pavement also some graphs were produced
for different types of material and loading which gives the length of cracks versus the number of
repeated loading. the results showed that with increasing the load distance from the initial place which
is initiated the stress intensity factor is increased in mode Ι and mode ΙΙ. Also increasing the stiffness
gradient in asphalt concrete due to temperature differential in top and bottom of asphalt layer or
differential increasing between stiffness of asphalt surface and asphalt base course will be increased
the stress intensity factor.