| Material property testing technique is an important means to evaluate the property index,durability and reliability of materials and finished products,which also plays an important role in the development of material science.Functional materials with electrical and magnetic functions,such as piezoelectric materials and ferroelectric materials,are widely used in the field of engineering technology.These materials are usually used in the coupled environment of multiple physical fields,and are not limited to their mechanical property.In order to study its property evolution under the practical use conditions,it is necessary to construct a multiple physical field coupling environment,such as the environment which Include force,electricity,heat and magnetic.The existing commercial testing machine mainly aims at testing the mechanical properties of materials under a single loading condition.It does not have the ability to test the comprehensive physical properties such as force,electricity and magnetism.At the same time,it is difficult to integrate with the microscopic imaging means and micro mechanical properties testing means.So it has been unable to meet the increasing demand of new materials science research.To solve the above problems,this paper has designed and developed the in situ property tester with multiple loadings and multiple physical materials.It carries out the mechanical loads of tension/compression,bending,torsion and fatigue.In the meanwhile,it allows multiple physical field coupling loading under the temperature,electric and magnetic field.The micro metallographic structure and infrared spectrum of the materials were observed simultaneously in the loading test by using an integrated in-situ observation module.The indentation module can also be used to test the micro mechanical properties of the materials.This tester can completely,truly and richly obtain various macro and micro performance indexes of materials in the practical use environment,and provide important test basis for material performance analysis,preparation and use.In addition,this paper has also analyzed further the measurement errors of in-situ testing instruments for mechanical properties of materials,established the error correction algorithm,and proposed methods to reduce errors from the perspectives of clamping mode,instrument and sample design.On this basis,the multi-physical field coupling test of magnetoelectric layer composites with ferroelectricity and ferromagnetism was carried out.The main results are as follows:(1)The development of multiple physical field coupling material performance testing systemIn view of the limitations of existing material performance testing instruments,the development of in-situ testing instruments for composite loading and multiple physical field coupling material performance was carried out.Some technical problems,such as space interference,high frequency stress and multidimensional prestressed coupling loading,have been solved by reasonable structure design.In the meanwhile,the loading test items including mechanical tensile,compression,bending,torsion,low cycle fatigue loading test function have also been integrated.The synchronization precision loading of multiple mechanical loads have been realized,and finally formed the multiple loads test environment.On this basis,the technical difficulties such as axial/radial variable magnetic field loading,long distance non-contact heating,adiabatic and electromagnetic compatibility have also been solved.Some other external physical field environment including high temperature,low temperature,electric field and magnetic field have been added,and formed a complex loading test environment with multiple load and multiple physical field coupling.In order to obtain the micro-area mechanical properties,deformation damage,micro-structure morphology and temperature field distribution on the material surface online during the test process,the instrument also integrates the material indentation test function and in-situ observation function,and provides a rich and effective means for testing the micro-mechanical properties of the material under the service conditions.A software for testing and controlling material properties is also developed,which can allow users freely configure test plans according to their requirements.The software can also analyze the comprehensive physical properties of materials by combining the theories of material mechanics,electricity and magnetism.The control performance of each independent loading module,including the rapidity and accuracy of the closed-loop control of load,speed and position,has been adjusted through debugging test.On this basis,the tests of multiple load and multiple physical field coupling materials including compression,high temperature,electric field,compression magnetic field,stretch and torsion,low temperature and bending,fatigue and indentation,have also been carried out.A total of five groups tests have been conducted,which means the whole loading test functions of the instrument have been covered.So the function of the instrument can also be tested while the performance of the tested materials is analyzed in complex environment.(2)Research on the error correction algorithm of deformation measurement for the problem of strain measurement error caused by incompatible for multiple loadingA tensile correction algorithm involving the stiffness of the instrument and the deformation of the non-standard segment of the specimen is proposed for the tensile test by using profile clamping.The standard segment of the specimen is acquired indirectly by modifying the data collected by the displacement sensor,and verifying the accuracy of the correction algorithm through experiments.In addition,comparing the measurement errors between the finite element analysis and experimental methods in the three kinds of clamping methods commonly used in small in-situ tensile testers.The characteristics of different clamping methods are studied,and the applicable occasions are obtained.The above correction method is simplified for the friction clamping and pin clamping.Finally,correcting the deformation measurement error of the torsion,compression and bending modules combing with the structural characteristics of the instrument,and proving the effectiveness of the modified algorithm under complex loads by the tensile-torsion and compression-bending composite load tests.(3)Research on magnetoelectric functional materials by using self-developed instrumentsFirstly,the test environment coupled with force-electrical and force-magnetic field is constructed for piezoelectric ceramics(PZT)and giant magnetostrictive alloys(GMM).The effects of external load and bias magnetic field on important ferroelectric and ferromagnetic performance parameters such as piezoelectric coefficient,dielectric constant,compressive magnetic coefficient,magnetic permeability and flexibility coefficient are measured and analyzed.The finite element model of magnetoelectric composites is established by using the function of Gibbs function combining the measured performance parameters of PZT and GMM in a multi-physics coupling environment.Then the numerical simulation of magnetoelectric layer composite material is carried out.The magnetoelectric conversion performance of the magnetoelectric layer composites is experimentally studied by the instrument-building force-magnetic coupling environment and compared with the numerical calculation results to verify the correctness of the theoretical model.According to the experimental and data simulation results,it is found that although the external load has an inhibitory effect on the magnetoelectric conversion effect of the magnetoelectric layer composite material,the load can be used to regulate the resonant frequency of the magnetoelectric member.In addition,it will obtain a relatively stable sensitivity coefficient in a wider range of bias magnetic fields with an appropriate external load enables when the magnetoelectric composite component is used as an alternating magnetic field sensor. |
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