In this paper, a two-dimensional computational model is proposed for predicting the initiation position and propagation path of subsurface CRACK of spur gear tooth flank. In order to simulate the contact of teeth, an equivalent model of two contacting cylinders is used. The problem is assumed to be under linear elastic fracture mechanic conditions and finite element method is used for numerical study. An initial subsurface CRACK is considered in the model at different DEPTHs. For each position of the initial CRACK, moving contact loading is applied to the part and value of DKII is obtained for the CRACK tips. The position of maximum DKII is selected as the location of CRACK initiation. It is shown that the subsurface CRACK appears at the maximum shear stress point. The maximum tangential stress criterion is used to determine the CRACK growth angle. The CRACK is incrementally propagated until the CRACK tip reaches the part surface and a cavity is formed on the tooth surface. Analyzing the stress field and stress intensity factors are performed in ABAQUS software. The obtained results for the DEPTH and shape of the spall are in good agreement with the experimental results reported in literature.

Gear systems are one of the most functional power transmission systems in the industry. CRACK is one of the common defects in gears which is caused by excessive loading, sudden impact and shortcomings in the gears construction. Initially, the CRACK will not result in structure collapse, but its growth can lead to irreparable damage. Therefore, detecting the CRACK and determining its location and DEPTH are very important in this respect. In this paper, two encoders are used to obtain the spur gear pair transmission error speed. Moreover, the short-time averaging method (STAM) has been proposed thereby detecting the CRACK location and some statistical indicators have been used to estimate the CRACK DEPTH in the spur gear tooth. For this purpose, a dynamical model in which mesh stiffness varying with time has been deployed to achieve the transmission error speed of the gear system. Additionally, a gear test rig including a single-stage gearbox, two encoders, and also an electronic board has been used. Encoders were installed on input and output shafts and the angular position of each shaft in time was saved in the computer using the electronic board. In addition, the transmission error speed was obtained by analyzing the received signals. Then, short-time averaging method was used to identify the CRACK location. Ultimately, some indicators such as ABS-max, FM0, Energy Ratio (ER) and Residual Signal Average were applied to the simulated results and experimental signals to fine the CRACK DEPTH ratio. According to  the results of this study, it seems safe to conclude that the STAM is a useful method in CRACKed tooth detection and the indicators have acceptable accuracy to find the CRACK DEPTH ratio.

Chloride ion ingress into concrete causes steel corrosion over time, thereby ending the service life of structures. Sometimes, it severely reduces the loading capacity of reinforced concrete and may even cause the sudden destruction of concrete structures. Concrete CRACKing stems from different factors, such as shrinkage and tensile stress due to thermal loading and under loading. Modeling and estimating chloride ion ingress into CRACKed concrete over different periods can facilitate the appropriate determination of structural lifetime and maintenance of reinforced concrete structures. Accordingly, this research investigated the effects of the width and DEPTH of concrete CRACKs on the rate of chloride ion diffusion and rebar corrosion. To this end, different concrete specimens characterized by various CRACKing conditions were modeled in COMSOL multiphysics. Analytical results showed that the critical CRACK that reflected the highest extent of chloride ingress into a specific region at different times was not necessarily the defect with the largest thickness and DEPTH. This finding highlights the importance of investigating CRACK behavior in the appropriate estimation of structural service life. Nevertheless, over time, considerably wide and deep CRACKs may ultimately be a reflection of the substantial rate of ingress.

To ensure the rail transportations safety, evaluation of fatigue behavior of the rail steel is necessary. High cycle fatigue behavior of a rail steel was the subject of investigation in this research using fracture mechanics. Finite element method (FEM) was used for analyzing the distribution of the stresses on the rail, exerted by the external load. FEM analysis showed that the maximum longitudinal stresses occurred on the railhead. To find out about the relation of CRACK growth with its critical size, and to estimate its lifetime, the behavior of transverse CRACKs to rail direction was studied using damage tolerance concept. It revealed that transverse CRACK growth initially occurred slowly, but it accelerated once the CRACK size became larger. Residual service life was calculated for defective segments of the rails. In addition, allowable CRACK size for different non-destructive testing intervals was determined; the allowable CRACK size decreased as the NDT intervals increased.