Experimental Study On Stress-damage Evolution Mechanism Of High Purity Copper By Micro-magnetic Monitoring

Copper is regard as the most common nonferrous metals,of which has the advantages of good ductility,tensile property and corrosion resistance,etc.The copper has been applied widely in electrical and electronic,transportation,machinery manufacturing and any other fields.In comparison to conventional copper,the physical properties of the high purity copper were more excellent.And in high technology areas such as superconductivity and aerospace,some of quite expensive rare metals has been replaced by high purity copper.Stress damage of non-ferromagnetic metal is one of the important damage and fracture of material under high strength load.Furthermore,stress damage is an essential security issues closely related with the using process.At present,material damage magnetic monitoring mostly focuses on the determination of the damage state of ferromagnetic materials by using the magnetism of the materials.In comparison to the ferromagnetic materials,the low magnetic saturation magnetization strength of non-ferromagnetic materials and the magnetic properties produced during stress damage state are very faint and tiny.Therefore,there are still many problems in research on non-ferromagnetic materials.Micro-magnetic testing technology as a new type of magnetic characterization nondestructive testing technology which provides the theoretical and experimental basses for judging the stress damage state of nonferromagnetic materials.However,the criterions for judging non-ferromagnetic materials stress damage state were not perfect yet.Thus,the experimental research about the damage evolution process of non-ferromagnetic materials stress damage based on magnetic characterization has been carried out.Firstly,taking the high purity copper as the research object,we construct a stressmagnetic monitoring system of high purity copper based on micro-magnetic testing technology for carrying out research on magnetic capability parameters.Additionally,the variation of magnetic flux density of non-ferromagnetic materials under different stress states was revealed.Secondly,on the basis of constructing the mapping relationship between internal microstructure of high purity copper and magnetic flux density signal,the Dislocation-Magnetic flux density model is established.Furthermore,the relationship between the magnetic flux density of high purity copper and dislocation density is analyzed by using Dislocation-Magnetic flux density model.And the feasibility of using macro magnetic signal to judge internal microstructure of materials is theoretically proved.Moreover,the micro-morphological characteristics of high purity copper is obtained by analyzing the chemical composition analysis and microscopic morphology defect areas of samples we prepared.By combining the varying macro magnetic signal with microstructure change during various stress states of high purity copper,a new micro-magnetic method for monitoring and analyzing the tensile stress damage state of high purity copper is proposed.Meanwhile,the difficulty of on-line monitoring and judging internal microstructure of high purity copper stress damage is solved.Next to the above studies,the Dislocation-Magnetic flux density model was established based on internal microstructure characteristics of high purity copper and magnetic flux density.The experimental results are as follows :The strain of high purity copper in the elastic deformation stage is 0%～5%,there is a small amount of dislocation,and the magnetic flux density does not change significantly;the strain increases to 5%～48% in the hardening stage,the dislocation density increases,a dislocation wall is formed at the internal lattice,and the magnetic flux density decreases with increasing tensile stress;when the strain at the necking fracture stage continues to increase to 48%～52%,the dislocation density of the internal lattice gradually stabilizes,accompanied by the appearance of sub-slip bands,and the number and density of slip bands increase,the magnetic flux density signal still exhibits pulsed fluctuation,which is no different from the previously collected signal in the hardening stage;the magnetic flux density drops abruptly when the fracturing occurs.The relationship between the stress damage state and magnetic flux density signal from the experiments can be confirmed by Dislocation-Magnetic flux density model.Owing to the current situation that the monitoring accuracy of high purity copper stress damage states by traditional nondestructive detection methods was low,a novel micro-magnetic method for monitoring and analyzing the stress damage state of nonferromagnetic materials is proposed.The test results show that the proposed Dislocation-Magnetic flux density model sufficiently reveal the relationship between internal microstructure and macro magnetic signal.This technique provides a strong theoretical and test basis for stress damage monitoring the non-ferromagnetic materials in practical engineering applications.