The objective of this study was to investigate the performance of pipelines repaired with carbon-fibre-reinforced polymer (CFRP) under external pressure. The repaired pipeline experienced defects in terms of thinning of its local inner wall. The three-dimensional finite element method was used to analyse the collapse pressure of repaired pipes with internal corrosion defects. The traction–separation law and interlaminar damage criterion were applied to simulate the collapse process of repaired pipes. The results show that the collapse pressure of the composite-repaired pipe increased and the CFRP significantly reduced the strain in the defect region. It was observed that the ovality of the corrosion defect region was reduced and that the repair effectiveness mainly depended on the length, thickness, and interlayer cohesion.

In this paper, the effects of different loading paths of axial tension and external pressure on the collapse pressure of sandwich tubes are studied by experiments and finite element models. The difference of the two loading paths is investigated. Eight experiments were carried out to study the influence of different loading paths on pipeline collapse pressure under the same geometric and material parameters. Parameterization studies have been carried out, and the results are in good agreement with the experimental results. The test and finite element results show that the loading path of external pressure first and then the axial tension (P→T) is more dangerous; the collapse pressure of the sandwich pipe is smaller than the other. Through parametric analysis, the influence of the axial tension and the diameter-to-thickness ratio of the inner and outer pipe on the collapse pressure under different loading paths are studied.

Shearer is one of the core equipment of modern fully mechanized mining equipment, which is an important milestone marking the leap forward of China's mineral resources from labor-intensive to mechanized and intelligent output. At present, the cutting part of most shearers adopts the structural form of multi-stage involute spur gear linkage. The complex and large number of transmission parts have the problems of complex spatial structure and low transmission efficiency in the implementation of long-distance transmission of large torque. This paper puts forward the improved design scheme of “two-stage spur gear - two-stage bevel gear - two-stage planetary gear which greatly reduces the energy loss in the normal working process of the equipment, improves the transmission efficiency, and simplifies the spatial structure. Based on the strength theory, the weight with optimal bearing capacity and minimum volume is determined as the objective optimization function. According to the multi index constrained boundary conditions, the optimal gear train design parameters are obtained by ant colony algorithm, and the design strength meets the use requirements.