بررسي عددي پارامترهاي شكست ترك انعكاسي در روسازي آسفالتي تحت بار ترافيكي

Numerical Fracture Analysis of Reflective Cracks in Asphalt Overlays Subjected To Traffic Loading

ترك‌خوردگي لايه‌ي آسفالتي يكي از مودهاي شايع خرابي در يك سيستم روسازي است. عوامل مختلفي در ايجاد و گسترش ترك‌ها نقش دارند كه مهم‌ترين آنها بار ترافيكي و اثرات دمايي است. در اين نوشتار يك رويه‌ي آسفالتي چندلايه كه شامل يك ترك انعكاسي است، زير جريان ترافيك )عبور چرخ‌هاي جلو و عقب يك خودرو در حال حركت به سمت ترك انعكاسي( به‌صورت عددي مورد تحليل قرار گرفته و پارامترهاي شكست لايه‌ي آسفالتي شامل ضرايب شدت تنش مودهاي كششي و برشي و همچنين ترم تنش T با مدل‌سازي اجزا محدود محاسبه شده است. تاثير فاصله‌ي چرخ‌هاي عقب و جلو خودرو از محل ترك، ضخامت لايه‌هاي آسفالتي، ضريب ارتجاعي لايه‌ي روكش و نيز طول ترك انعكاسي ايجادشده در لايه در مقادير پارامترهاي شكست مورد بررسي قرار گرفته است. فاصله‌ي قرارگيري خودروي متحرك نسبت به ترك انعكاسي و نيز طول ترك، موثرترين پارامترها در مقدار و علامت پارامترهاي شكست هستند.

Cracking of asphalt layers and pavements is one of the most common modes of failure in roads and highways, which can significantly increase the cost of repair and rehabilitation. Since asphalt mixtures can behave as brittle materials at low temperature, brittle fracture and crack growth in pavements is usually observed at the surface of roads located in cold regions. Traffic loading, (due to the weight of moving vehicles) and thermal stress (induced by daily or seasonal variations of field temperature), are two major parameters affecting nucleation and propagation of cracks inside the pavements. Reflective cracking is often observed in the overlays, and the growth of such cracks is a an important problem in this field. Thus, understanding the mechanism of crack growth is essential for predicting pavement performance for designing the averlay thickness, as well as in the design and optimization of mixtures. In this study, a two-dimensional multi-layer asphalt pavement containing a reflective crack, and subjected to traffic loading of the front and rear wheels of a moving vehicle, was analyzed numerically using ABAQUS finite element code. Three fracture parameters, including modes I and II stress intensity factors (KI and KII) and the T-stress, are computed for various positions of the vehicle relative to the reflective crack. In the analyzed models, the influence of some parameters, such as wheel positions relative to the crack, elastic modulus, thickness of layers and crack length, was studied on the sign and magnitude of fracture parameters. According to the obtained results, an asphalt layer containing a vertical reflective crack experiences different mixed mode opening-sliding (mixed mode I/II) deformations when a vehicle moves from far distances towards the crack location. It was observed that a wide range of positive and negative KI, KII and T-stress values is induced in the asphalt layer. The influence of crack length on the fracture behavior of the analyzed crack was also noticeable.