A Study of Influence of Temperature on Crack Propagation Behavior of Asphalt Concrete
The fracture resistance of asphalt materials significantly influences the service life of asphalt pavements and consequently affects the maintenance and rehabilitation costs of the pavement network. Therefore, there is significant interest in understanding the mechanism of fracture in asphalt pavements and in developing analysis tools that would lead to the selection of asphalt materials with increased fracture resistance. Study of cracking behavior of asphalt mixtures should be conducted in a micro-scale level to have a real simulation of crack propagation. Using SIEMENS SOMATOM plus X-ray CT (computerized tomography) and multi-functional testing rig, a dynamic observation of cracking propagation of hot mix asphalt was conducted in this research. Failure process under compressive pressure was recorded using CT images and CT numbers. The direct responses in density change of Marshall Samples under a CT-compressive process are change of CT numbers. Cracking propagation in the samples can be clearly observed and failure mode and stress-strain behavior can then be simulated. The tests reported provide important theoretical fundamentals to study the cracking behavior and failure mechanism of asphalt mixtures Under the influence of temperaturet.
Development of a new yielding criterion: The Yeh-Stratton criterion
Abstract A new criterion responsible for the first yielding of a material is presented: the Yeh-Stratton criterion (the Y-S criterion). The Y-S criterion requires three yield strengths in simple tension, compression and torsion. It can be shown that the Y-S criterion is applicable to a brittle material as well as to a ductile material. The yield surface of the Y-S criterion is bounded and compatible in the σ-τ plane, the σ1-σ3 plane and the σ1-σ2-σ3 plane. It also predicts the angle of failure.
Failure analysis for poor solderability of Au surface of PCB
Nonwetting is one of the common problems and is always rejected in electronic assemblies. ENIG pads of a PCBA exhibited nonwetting after lead-free reflow soldering. With the aid of stereomicroscope, SEM&EDS and XRF, a series of analysis was performed. And after visual inspection, surface and cross section analysis, thickness measurement and solderability test, it can be inferred that oxidation of plating surface was the main reason for nonwetting, and corrosion in Ni plating caused an adverse impact on solderalibity.