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In the present study, the evaluation technique of fracture loads for blunt U-shaped notches is investigated using two fracture criteria, i.e. the mean stress based line criterion and the volume-based strain energy density (SED) criterion, and Filippi’s stress equation. It is found that under certain geometric conditions the fracture loads of blunt U-shaped notches can be evaluated by not only the generalized notch stress intensity factor K IC U , R , but also the maximum stress at the notch root σ maxC , and both the values of K IC U , R / K IC and σ maxC / σ C can be expressed by a function of ρ / ( K IC / σ C ) 2 . Two techniques are essentially equivalent. The geometric conditions can be estimated from the condition that the mean stress or the average SED over the control region in the actual specimens can be approximately evaluated by Filippi’s stress equation.

In this paper, the coherent gradient sensing (CGS) method is extended to study the local stress fields and fracture behavior of a blunt V-notch tip. First, the optical governing equations of the CGS method are derived based on Filippi’s stress equation for blunt V-notches and the concept of the notch stress intensity factor (NSIF). Moreover, the CGS fringe patterns in the vicinity of the blunt V-notch tip with different opening angles and notch radii are theoretically synthesized. Next, the fracture property of a blunt V-notch is experimentally studied using a series of three-point-bending polymethyl methacrylate (PMMA) specimens with different geometrical configurations. Finally, the generalized NSIFs up to the initiation of a fracture are evaluated using the proposed CGS method. The CGS fringe patterns in the experimental results exhibit a reasonable agreement with the theoretical fitted fringes, and the NSIFs and notch fracture toughness at the blunt V-notch tip are consistent with those obtained in previous theoretical studies and finite element simulations.

In the present paper, in order to investigate systematically the effectiveness of Filippi’s stress equation applied at evaluating stresses generated in a rounded V-shaped notch with a finite depth, the stresses generated in a semi-infinite plate with rounded V-shaped notch subjected to a uniform tension load at remote are used as a base data to examine the applicability of Filippi’s stress equation. It is found that Filippi’s equation gives an excellent approximation to the stresses along the notch bisector for rounded V-shaped notches. The generalized stress intensity factor K ρ , I V ( r ) is almost constant along the notch bisector in the region where the stresses are governed by the singular stress field in a sharp notch; the peak discrepancy between Filippi’s equation and the numerical analysis is less than 7% when the notch opening angle γ = 0 ° , 2.5 % when γ = 30 ° and 5% when γ = 90 ° and 120°. Also it is found that Filippi’s equation is effective in evaluating the stresses along direction different from the notch bisector, however, as the calculation angle θ with respect to the notch bisector increases, the discrepancy between Filippi’s equation and the numerical analysis becomes larger. Therefore, it is advisable to limit calculation points of stress within a range of θ ⩽ 30 ° . Moreover, values of the maximum stress σ max predicted by various techniques are also examined using the numerical-analysis results of the semi-infinite plate with a V-shaped notch, and an analytical approach for predicting the constant a 1 in Filippi’s equation is proposed.

Weight has a significant effect on the mobile performance of a robot. A coal mine rescue robot (CMRR) is a special type of mobile robot and is relatively heavy because it is explosion proof. In this study, a simple optimization method is proposed for the design of a lightweight, explosion-proof housing of a CMRR. A stress analysis of the individual panels is performed first and ANSYS software is used to perform a stress analysis of multiple stiffened panels. A simple stress equation is developed based on the results and represents the basis of the optimization method. Subsequently, the optimization equations of the explosion-proof housing are developed and the explosion-proof housing of the CUMT-IV robot is designed. Explosion tests were conducted using a physical prototype to verify the strength of the explosion-proof housing. Further, two simple guidelines are developed based on the optimized results to reduce the design difficulty for engineering applications. The simple optimization method proved suitable for designing the explosion-proof housing.

High performance turf reinforcement mat (HPTRM) has emerged as an effective and flexible strengthening system to protect earthen levees against the erosion caused by overtopping flows. The purpose of this study is to characterize the erosion and failure processes of HPTRM-strengthened levees under combined wave and surge overtopping. The Erosion Function Apparatus (EFA) is used to analyze the erodibility of HPTRM-strengthened clay. The erodibility parameters such as critical shear stress and erodibility coefficient are then obtained. A HPTRM-element model is proposed to account for the mechanism of HPTRM in protecting cohesive soil with the help of EFA results in the characterization of the grass mat strength parameter. At last, a failure model is developed based on the excess stress equation, and the durations of HPTRM-strengthened levees against combined overtopping with different wave heights and freeboards are presented.

The effect of cutting conditions such as numbers of tool teeth, depth of cut and cutting speed on the cutting resistance about 12%Cr steel hasn't been studied before. So the effect of cutting conditions on the cutting resistance will be investigated in this paper. The relationship between cutting resistance and work damaged layer will be taken into consideration. The results are as follows. (1)The cutting resistance becomes larger with the increase of the depth of cut and the numbers of tool teeth. It has no relation with cutting speed. (2)The depth of work damaged layer increase with the increase of the depth of cut and numbers of tool teeth. It does not change with the increase of cutting speed. (3)The deformation of cutting surface becomes larger with the increasing depth and numbers of tool teeth. It changes a little with the increase of cutting speed. (4)It was found that the depth of work damaged layer increased with the increase of the cutting resistance. The depth of work damaged layer is thought to have an intimate relation with the cutting resistance. (5)The experimental value for work damaged layer by hardness measuring is thought to be reasonable value, because the experimental value is nearly equal to the evaluated one obtained from Sokolovskii's stress equation.

Multiscale dislocation dynamic simulations are systematically carried out to reveal the dislocation mechanism controlling the confined plasticity in coated micropillar. It is found that the operation of single arm source (SAS) controls the plasticity in coated micropillar and a modified operation stress equation of SAS is built based on the simulation results. The back stress induced by the coating contributes most to the operation stress and is found to linearly depend on the ‘trapped dislocation’ density. This linear relation is verified by comparing with the solution of the current higher-order crystal plasticity theory and is used to determine the material parameters in the continuum back stress model. Furthermore, based on the linear back stress model and considering the stochastic distribution of SAS, a theoretical model is established to predict the upper and lower bound of stress–strain curve in the coated micropillars, which agrees well with that obtained in the dislocation dynamic simulation.

An accelerated ultrasonic fatigue test (UFT) was used for analyzing very high cycle fatigue (VHCF, Nf > 10 ) behaviors of a specimen with a test resonance of 20 kHz. Using the finite element method (FEM), the dynamic behaviors of the specimen was studied by calculating the stresses along its gauge portion, with displacement. The shape of gauge portion profile was assumed to be a hyperbolic according to the stress equation of the UFT. However, as the specimen used in the test had a circular arc profile, the FEM was used for studying the local stresses for two cases of the gauge profile. The results were compared with those obtain from the stress equation of the UFT. The dynamic behavior of the gauge portion could be understood for further comparison with the actual results.

In the previous paper of the authors (Chen and Fan, 2019), the fracture evaluation of the U-shaped notches, which refer specifically to the V-shaped notches with the notch opening angle γ = 0 , has been investigated in details. In the present study, the evaluation technique of fracture loads for blunt V-shaped notches is investigated by using the mean stress criterion and the Filippi’s stress equation. It is found that the conclusions obtained in the previous study for the U-shaped notches with γ = 0 can also apply to the V-shaped notches with γ ≠ 0 . Under certain geometric conditions the fracture loads of blunt V-shaped notches can be evaluated not only by the generalized notch stress intensity factor K IC V , R , but also by the maximum stress at the notch root σ maxC . Both the values of K IC V , R / K IC and σ maxC / σ C can be expressed by a function of ρ / ( K IC / σ C ) 2 . The geometric conditions can be estimated from the condition that the mean stress over the control region in the actual specimens can be approximately evaluated by Filippi’s stress equation.