The Neutron Diffraction Stress Analysis Of Beryllium

Hexagonal close-packed(hep)metal beryllium with a special structural functional material,which possesses the excellent properties,has been extensively used in nuclear energy,aerospace and other fields,such as the first wall material and inertial navigation device for fusion reactor.The mechanical properties,deformation mechanism and residual stress change of beryllium metal has attracted much more concerns.In this paper,the neutron diffraction stress of beryllium metal was measured by testing of in situ loading and residual stress,which contains four works:in situ loading experiment at room temperature,testing of residual stress,effect of outer metal and designing of safety protection device.The first part is to study the effect and mechanism of different initial microstructure on the mechanical properties of polycrystalline metal beryllium.Three different kinds of microstructures have been achieved in beryllium,by different pre-deformation strategies,which are compression at(i)room temperature(RT)and the strain rate of 10-3 s-1,(ii)600 ? and 10-3 s-1,and(iii)RT and 103 s-1,respectively.The mechanical properties of the polycrystalline beryllium are consequently tailored.It is found that,the compressive mechanical response is the hardest for the sample quasi-statically pre-deformed at RT,while is the softest for the dynamically pre-deformed one.The underlying mechanism has been revealed by the optical morphology characterization,macro-texture analysis and in-situ neutron diffraction measurement.The sample quasi-statically pre-deformed at RT possesses the 'weak texture' type of initial microstructure,for which the(00.2)plane preferentially bears the compressive strain during the microscopic mechanical response.Due to the combined effects of the initially preferred microstructure and induced dislocation,this sample exhibits the relatively obvious deformation-hardening with respect to the other ones.The sample dynamically pre-deformed at RT has the 'strong texture' type of initial microstructure and some micro-voids.For the dynamical pre-deformed sample,the(00.2)plane also mainly bears the compressive strain during the microscopic response.However,the deformation-hardening effect is weakened because the existing micro-voids participate the stress partition.The sample quasi-statically pre-deformed at 600 ? possesses the 'random orientation' type of initial microstructure.Each plane for this sample bears the compressive strain equally at the preliminary stage during the microscopic response and then the lattice strain for(11.0)increases with the increase of loading stress.For such case,the deformation accommodation inside the sample becomes relatively easier due to the decreased dislocation density.It suggests that the controllable mechanical properties can be realized through collaborative configurations of microstructures at different scales.The material properties can be customized through the microstructure engineering to meet the particular service requirements.The second part is mainly to test the residual stress of different configurations of beryllium weldments in light of combined with the actual application of engineering.Four different welding parts were selected.Beryllium(11.0)and steel(31.1)crystal surface was used as the test crystal surface,and the three-dimensional residual stress was measured at the radial,axial and tangential directions at different depths of the weld center,and the residual welding parts of different materials were compared and explored its distribution rule of residual stress.The results shows the welding of the same beryllium-beryllium material,whether ring or sheet,has little thermal stress,the axial stress is mainly tensile stress and the tangent is mainly compressive stress,and the difference of stress distribution between the two configurations is small,but the amplitude of the axial stress of the flake configuration increases with the distance from the center.The thermal stress of the dissimilar beryllium-steel material is larger than that of the former,and the stress value decreases with the increase of the distance from the weld,and the tensile pressure is unbalance between the beryllium steel,the axial compression of the beryllium material,the axial compression of the steel,the tangent tension,the force relation of the beryllium and steel tension and pressure is just the same.There is a large difference between the two configurations.The main force direction of the ring type is tangential and axial,while the main direction of the force is axial,and the stress distribution of the steel is relatively stable compared with the two materials,and the stress distribution of the beryllium material shows the complexity.The distribution rule of welding residual stress of beryllium materials with different configurations and processes is summarized,so as to provide technical support and reference for related engineering stress.In third part,the effect of outer metal on the neutron diffraction strain stress of beryllium material is studied by taking the steel-beryllium combination as an example.the influence of the thickness of the stainless steel beryllium composite on the shape and strength of the neutron diffraction peak of the beryllium material is carried out by placing three kinds of stainless steel slices with different thickness(1 mm,2 mm and 3 mm)on the surface of a 5 mm thickness beryllium plate.It is found that with the increase of the thickness of the external stainless steel,the neutron diffraction peak intensity of the internal beryllium material will become weaken,the diffraction peak will shift to the high angle,and the linear relationship exists between them and the thickness of the stainless steel.The neutron diffraction strain and stress test of the beryllium material in the steel beryllium composite should be modified by the following formula ?true =?m+90·t,?true=?m+27·t,and the actual strain and stress are all higher than the strain and stress tested.t is stainless steel thickness.The fourth part is to design the corresponding safety protection device for the room temperature and high temperature experiment.It mainly includes system design and set up,and focuses on the preparing of the sealed tension device.The excellent tightness is a key for the neutron scattering experiment of metal beryllium,and efficiently prevents its threat to researchers.In addition,the special pressure clamp is also designed and used in the neutron diffraction experiment.The concentration of beryllium in workplace is detected by fluorescence spectrophotometric method according to the corresponding standard,and the comprehensive Lumina fluorescence spectrophotometer is also set up.In the view of cleaning and dust removal system,the scheme for purifying the powder and steam produced by the mechanical experiment of beryllium is designed and formulated in combination with the actual situation of the site and the special discharge standard.