Fault Diagnosis Method For Reciprocating Compressor Under Complicated Working Conditions Based On Deep Transfer Learning

It is fundamental to perform research on rock fracture process,which provides a key assistance for the analysis of crustal movement and seismic activity,and the safety of mining engineering.A deep knowledge of pure shear fracture,including its evolution,mechanical behavior,and interaction during fracture damage,is a fundamental significance to improve rock fracture mechanism and engineering applications.Pure shear fracture,as a fracture under the loading of pure shear,represents a typical fracture in rock-type materials.It is also a fundamental research topic in rock fracture mechanics.As different to the condition of small scale yielding that follows the assumption of linear elastic fracture mechanics(LEFM),a pure shear fracture under large scale yielding is not a mode Ⅱ/sliding mode fracture,and its initiation and propagation are influenced by the fracture process zone(FPZ)in front of the crack.Its consequence is the challenge to predict pure shear fracture under the large scale yielding.This research studies pure shear fracture in rock-type materials under the large scale yielding,based on rock compression and digital image correlation in the laboratory.The concentrations of this research are:(1)prediction and experimental validation of the initiated fracture trajectory;(2)evaluation of local shear influence;(3)evaluation of fracture prediction by fracture criterion(e.g.,local symmetry criterion).The main achievements and conclusions are:(1)the assembly of a monitoring system and the introduction of testing approach based on digital image correlation to study pure shear fracture.Based on analysis of specimen size,pre-created crack,loading mode,the boundary conditions and observation surface,three types of specimens were tested: the angled edge crack semi-circular specimens under three-point bending(SCB),the centrally cracked Brazilian disk(CCBD)specimens,and double edge notched compression(DENC)specimens.The measurements of specimen surface displacements are realized during pure shear fracture experiment,with the assistances of the image capture system by C++,mechanical loading system,image analysis algorithm by Matlab.(2)the understanding of fracture mechanism such that a curved fracture is the consequence under the influence of the local k Ⅱ stress intensity.The main reason for a curved fracture is because a local k Ⅰ stress intensity can be produced in the tip region,such that the fracture opens perpendicular to the direction of the maximum k Ⅰ.Simultaneously,there is a local k Ⅱ stress intensity along the direction,which will kink the initiated fracture continuously.The gradual removal of the local k Ⅱ during the fracture kinking is due to a fact,i.e.,tensile resistance of rock-type materials is much smaller than the shear resistance.(3)the demonstration of non-symmetric distribution of normal/opening displacements along the FPZ that is related to the local shear influence.Based on fracture mechanics,there are two characteristics for a pure mode Ⅰ fracture: no sliding displacements and a symmetric distribution of opening displacements.It is difficult for openings to have a non-symmetric pattern,if there is no local shear stress.In addition,comparison between mode Ⅰ and mixed-mode fractures under three-point bending reveals that the mixed-mode fracture does not involve any sliding displacements,but its normal displacements are not symmetric.Indeed,it supports the correlation between the local shear stress and non-symmetric pattern of normal/opening displacements.(4)the evaluation approach that is proposed to characterize the local shear influence,based on the introduction of a parameter η.To study the local shear influence on rock fracture process,and with a full help of the measured displacements by digital image correlation,parameter η is the ratio of the normal/opening displacements at the two sides of the FPZ,which represents the symmetry degree.The minimum value of the η is set to 1,such that a larger η corresponds to a larger shear influence.A pure mode Ⅰ fracture,when η is 1.(5)the examination of three potential fracture trajectories after the fracture initiation and propagation in rock-type materials under large scale yielding.Experimental results from the SCB,CCBD,and DENC specimens show: after the first fracture kink,three types of potential fracture directions are observed: when parameter ηdecreases from a finite value(larger than 1)to 1,the local shear influence decreases and the fracture turns its direction to where the influence is smaller;when parameter ηmaintains a finite value within a range 1.5-2.5,the local shear influence does not change and the fracture maintains the current direction;when parameter η increases from a finite value(larger than 1)to the infinity,the local shear influence increases and fracture direction will change to where the influence is larger.(6)the mechanism of the local shear influence that dominates on the fracture direction under large scaling yielding.Under small scale yielding,pure shear fracture only turns to one direction where the k Ⅱ is smaller.In contrast,large scale yielding involves three different directions,posing a challenge for fracture criterion to predict.The first fracture kink will decide fracture direction,but the experimental observations have a substantial difference to the prediction(76°)by the local symmetry criterion under small scale yielding.Experimental results show a correlation between the angle of the first kink and the change of the local shear.If the local shear is reduced,the angle is larger than 76°;if the local shear is not reduced,the angle is smaller than 76°.