Estimation of Internal Maximum Thermal Stress of Tunnel Side Wall Lining Concrete During Construction Period

Thermal cracks in lining concrete of large section hydraulic tunnel usually occur in side walls during construction, and most of them are harmful penetrating cracks. In order to meet the needs of real-time rapid control for engineering design in construction period, nine influencing factors of maximum tensile of side wall lining concrete σmax during construction period are determined on the basis of comprehensive analysis of temperature stress effects and finite element simulations, and their influencing regularities are analyzed. Then the estimation formula of σmax and real-time control method of thermal crack are put forward. Through the application of real-time temperature control and crack prevention control of lining concrete in flood discharge tunnel, the estimation formula of σmax and the real-time thermal crack control method are proved to be correct and applicable.

Tool wear analysis in milling of locomotives wheels

The present work aims to evaluate the tool wear during the milling process of locomotives wheels—class C. A digital microscope is used to identify both the wear and the damage. The wear or damage, when propagated, can compromise the wheel roughness, which has a significant economic importance to railroad maintenance. A system for image capture composed of an ISM-PM200S INSIZE Digital Microscope and the ISM-Pro software is used to measure the flank wear. Firstly, milling process is applied with different numbers of passes. The results showed that, after flank wear, the most common wear is the thermal crack. It is also possible to observe the appearance of chipping and fracture as a consequence of the combination of thermal and mechanical cracks in the same insert. The inserts are more damaged in the raceway, due to the hardening of this region during its use. Inserts in the frieze region also showed higher values of wear, justified by the conditions of the railway. The highest values observed are around 0.1 mm. It is possible to notice that some inserts showed other damages, such as breaks and chipping, even before reaching the end of life due to wear.