激光粉末床成形316L不锈钢多孔结构力学性能研究

Mechanical Properties of 316L Stainless Steel Porous Structure Formed by Laser Powder Bed Fusion

以激光粉末床熔融(LPBF)技术成形的316L不锈钢体心立方型(BCC)多孔结构为研究对象,利用有限元分析法对不同长径比杆件的体心立方型多孔结构进行了准静态压缩过程模拟,分析了其微观力学响应和应力-应变特性。制备了体心立方型316L不锈钢多孔结构样件,对样件进行了准静态压缩试验,分析了具有不同几何参数的多孔结构的应力-应变特性和变形失效机制,并对比分析了仿真和力学试验的结果。研究结果表明:当成形样件杆件的直径从0.4mm增加到1.2mm时,杆件直径的相对误差从15.00%下降到6.08%,直径越大,相对误差越小,等效弹性模量从59.87MPa增加到3356.21MPa,压缩屈服强度从1.02MPa增加到33.88MPa;有限元分析法与力学试验得到的等效弹性模量和压缩屈服强度的平均相对误差分别为9.11%和7.86%。

Objective The metallic porous structure has great application prospects in lightweight.Aiming at the demand of further improving the lightweight level in aerospace,automobile,mechanical equipment and other fields,this paper uses the theories and methods of finite element analysis combined with the microscopic inspection analysis and the mechanical test research.The mechanical properties of porous structures under quasi-static uniaxial compression are systematically studied based on the laser powder bed fusion(LPBF)technology and by taking the 316Lstainless steel porous structure as the research object.In this study,five kinds of body centered cubic(BCC)porous structures with different sizes are designed,and these samples are fabricated using LPBF.The compression test and the finite element analysis of porous structures are conducted.The design and manufacturing feasibility of metal 3Dprinting lightweight structures based on the LPBF technology is verified.Methods First,the BCC porous structures with five different aspect ratios are modeled by the SolidWorks software,and subsequently the quasi-static simulation analysis is carried out by the ABAQUS software.The samples are prepared by Renishaw AM400,and the aerosolized 316L powder is selected as the test material.By selecting point distances,exposure time,laser powers,and scanning distances as the orthogonal test factors,the optimal process parameters for forming the 316L stainless steel are obtained.The macroscopic morphology of the sample is observed by an optical microscope and the microscopic surface morphology of the sample is observed by the scanning electron microscope.Then,the sample is subjected to the uniaxial compression test at room temperature with the UTM5305 electronic universal testing machine.Finally,the mechanical properties of the 316L porous structure are analyzed according to the simulation and test results,and the reasons for the difference between the two results are compared and analyzed.Results and Discussions From the simulation results,the stress distribution of the BCC porous structure in the compression process is that the stress level in the central region is low,and that in the surrounding region is high(Fig.7).The displacement distributions of the five sizes of porous structures are consistent.The plastic yield first occurs at the node,and the yield mode is bending at both ends(Fig.8).In the deformation process of the porous structure,elastic deformation first occurs,and then the porous structure begins to yield with the increase of strain(Fig.9).From the test results,the microscopic surface of the sample is rough,and there are unmelted metal particles and cataphracted morphologies(Fig.15(b)).For the porous structures with different sizes,the forming accuracy increases with the increase of rod diameter and volume fraction(Tables 3 and 4).During the whole deformation process of the compression test,the strain is mainly concentrated in the diagonal,especially in the central region,but the overall flexibility is high(Fig.17).In the range of 10%strain,the results of finite element analysis and mechanical experiment are consistent,and the curve trend is consistent(Figs.10 and 16).The average relative errors of the equivalent elastic modulus and compressive yield strength obtained by the finite element analysis and the mechanical test are within 10%(Table 5 and Fig.18).Conclusions The BCC 316Lporous structure is prepared based on the LPBF technology.The compression process of this porous structure mainly experiences the elastic stage,platform stress stage and densification stage.By observing the morphology and measuring the geometric parameters of the porous structure,when the diameter of the rod is from 0.4mm to 1.2 mm and the volume fraction is from 4.9%to 35.75%,the relative errors of diameter and volume fraction are from 15.00%to 6.08%and from 8.20%to 6.03%,respectively.It can be seen that the forming effect is good,and the contour error and surface sticking are the main causes of the error.The larger the size,the higher the forming accuracy.With the increase of rod diameter,the equivalent elastic modulus increases from 59.87 MPa to3356.21 MPa,and the compressive yield strength increases from 1.02 MPa to 33.88 MPa.The research conclusions of the finite element analysis and the mechanical test are compared and analyzed.The average relative error of equivalent elastic modulus obtained by the finite element analysis and the mechanical test is 9.11%,and the average relative error of compressive yield strength is 7.86%.Both are within 10%.Therefore,the finite element model can effectively predict the mechanical properties of the 316Lstainless steel body-centered cubic porous structure within a certain error range.