基于梯度密度的非均质蜂窝结构面外压缩性能及优化设计

提出了一种胞元相对密度呈梯度分布的非均质蜂窝结构,采用参数化设计方法建立了模型,基于试验和有限元分析,研究了梯度系数和胞元尺寸对梯度密度蜂窝结构在面外压缩条件下变形模式和力学响应的影响,并进一步对梯度密度蜂窝结构的吸能特性进行了优化设计。仿真结果表明,在面外准静态压缩条件下,梯度密度非均质蜂窝结构的变形模式与普通蜂窝相似,梯度系数对初始峰值应力的影响较小,具有一定面内正梯度的蜂窝具有更高的平台应力,结构比吸能随着梯度系数的增大而增大。蜂窝初始峰值应力随胞元尺寸的增大而小幅提高,结构比吸能随胞元尺寸的增大先减小后增大。优化结果表明,优化后的梯度密度蜂窝结构峰值冲击力下降了74.3%,比吸能提升了1.6%。     

激光选区熔化TC4钛合金点阵结构的压缩性能

通过增材制造成型复杂晶格结构,实现航空航天结构件的轻量化设计得到越来越多的应用,然而点阵结构设计及其性能评价仍欠缺。本研究采用金刚石结构为基体,以点阵密度、结构形式为目标,设计不同几何参数试样,并以TC4钛合金为对象进行激光选区熔化(SLM)成型。对成型试样进行压缩试验,研究这种结构不同尺寸试样压缩性能的差异。结果表明:金刚石点阵结构试样受到载荷后应力在连接节点位置集中,产生断裂。提高晶胞密度可以缓解应力集中现象,提高比强度。减小晶胞尺寸和添加外壳都可以使应力均匀化,提高性能稳定性。小晶胞尺寸试样对球化现象、孔隙等冶金缺陷较为敏感,造成强度的下降。     

单胞构型和结构参数对SLM成形梯度点阵结构压缩性能的影响

梯度点阵结构由于压缩时具有优秀的吸能能力,目前常作为吸能组件被应用于航天、国防和医疗等领域。但随着现代工业的发展,工程领域对其压缩性能提出了更高的要求,为使其进一步优化,有必要探讨单胞构型、结构参数和压缩性能之间的关系。因此本研究通过选区激光熔化(Selective laser melting, SLM)成形了两种梯度差的AlSi10Mg变杆径梯度体心立方(Body-centered cubic, BCC)和金刚石(Diamond, Diam)结构,以研究梯度差对压缩性能的影响,并对两种单胞构型进行对比。准静态单轴压缩实验和有限元分析(Finite element analysis, FEA)的结果表明,在同相对密度下,当单胞构型相同时,随着梯度差的增加单位体积吸能量明显增加。而梯度差相同时,Diam梯度点阵结构的压缩模量、屈服强度、抗压强度和最大峰值应力均高于BCC,同时其单位体积吸能量和吸能效率也高于BCC。     

激光选区熔化TC4钛合金点阵结构压缩性能研究

通过增材制造成型复杂晶格结构,实现航空航天结构件的轻量化设计得到越来越多的应用,然而点阵结构设计及其性能评价仍欠缺。本研究采用金刚石结构为基体,以点阵密度、结构形式为目标,设计不同几何参数试样,并以TC4钛合金为对象进行成型。对成型试样进行压缩试验,研究这种结构不同尺寸试样压缩性能的差异,结果表明：金刚石点阵结构试样受到载荷后应力在连接节点位置集中,产生断裂。提高晶胞密度可以缓解应力集中现象,提高比强度,减少晶胞尺寸和添加外壳都可以使应力均匀化,提高性能稳定性。小晶胞尺寸试样对球化现象、孔隙等冶金缺陷较为敏感,造成强度的下降。     

Al基和Al-6Si基闭孔泡沫铝的动态吸能性能

利用熔体转移发泡法制备不同基体成分不同密度的闭孔泡沫铝,从能最吸收能力、能量吸收效率以及能量吸收图等方面对其动态吸能性能进行研究.结果显示:无论是Al基还是Al-6Si基的闭孔泡沫铝,能量吸收能力随应变的增加而增大,且随相对密度的增加,能量吸收能力先增加后减小;能量吸收效率的变化具有明显的缓慢增加、趋于平缓和缓慢减小的特征;随着应力的增加,闭孔泡沫铝单位体积的吸能能力先快速提高,达到一定值后上升趋势减缓,出现明显的肩;对应此密度的闭孔泡沫铝可以提供最大容许应力σp,且随着相对密度的减小,最大容许应力σp逐渐减小;相同密度Al基和Al-6Si基的闭孔泡沫铝能量吸收能力相比,前者的要大一些,但Al-6Si基闭孔泡沫铝的吸能效率要比Al基闭孔泡沫铝的吸能效率高,且最高吸能效率比较稳定持久.     

激光3D打印AlSi10Mg铝合金点阵结构材料的组织和力学性能

以不同激光3D打印参数制备了AlSi10Mg铝合金点阵结构材料,探索其最优化打印参数,研究了铝合金点阵结构材料的组织和性能,以及后续热处理对其组织性能的影响。结果表明,最优化打印参数为:环境温度80 ℃,粉层厚度30 μm,激光束直径80 μm,激光能量370 W,激光扫描速度1300 mm/s。制备的铝合金点阵结构材料空洞缺陷少,致密性高,显微组织呈一层层交错堆垛的激光熔池,为细小的α-Al等轴胞状晶和球状Si颗粒相组成,性能良好。经热处理后,原激光熔池缺陷、等轴胞状晶特征消失,Si颗粒相不断析出并长大,硬度和静态压缩试验下的平台应力降低,压缩性能下降。     

选区激光熔化成形点阵结构的各向异性对力学性能的影响

选区激光熔化技术（selective laser melting, SLM）成形的金属点阵结构由于具有结构设计自由度大、轻量化、缓冲吸能等优势,在航空航天等领域具有广泛的工程应用前景,然而对其力学性能的研究不够充分。本研究设计了不同方向的体心立方（body-centered cubic, BCC）和金刚石（Dia）两种晶胞点阵结构,基于SLM技术成形了AlSi10Mg点阵结构,并对成形试样进行了压缩试验,结合有限元分析（finite element analysis, FEA）研究了点阵结构的各向异性对其压缩响应和吸能特性的影响。结果表明,两种点阵结构均存在明显的各向异性。在相对密度基本一致的情况下,点阵结构方向从0°到45°,随着角度的增大,屈服强度明显增大,BCC点阵结构的各向异性对其压缩屈服强度的影响更加明显,Dia点阵结构的屈服强度明显高于BCC点阵结构。不同方向点阵结构的比吸能(specific energy absorption, SEA)存在明显差异,点阵结构方向从0°到45°,随着角度的增大,SEA明显增大,Dia点阵结构的SEA明显高于BCC点阵结构。不同方向点阵结构的碰撞载荷效率(crash load efficiency, CLE)存在明显差异,BCC点阵结构在0°方向取得最大值1.07,并随着点阵结构角度的增大逐渐减小,Dia点阵结构CLE随着点阵结构角度的增大而增大,并在45°方向上取得最大值1.01。     

模拟正火温度对Q355E钢锻件组织和性能的影响

利用模拟程控热处理炉进行300 mm×300 mm截面Q355E钢锻件心部材料的模拟正火处理试验,通过光学显微镜、扫描电镜、拉伸和冲击试验机,研究模拟正火温度对厚截面风电法兰用Q355E钢锻件组织和性能的影响。结果表明,模拟正火温度由780 ℃升高至900 ℃,并经580 ℃回火后,材料-50 ℃冲击吸收能量呈现先增加后降低的趋势,铁素体平均尺寸由14.73 μm降低至12.07 μm又增大至15.02 μm,珠光体的平均尺寸从3.69 μm增大至10.51 μm;模拟正火温度为820 ℃和840 ℃时,铁素体和珠光体组织均匀细小,珠光体呈条状和近等轴状分布,-50 ℃冲击吸收能量为183.8~211.1 J,试样剪切断面率在50%以上。对于300 mm×300 mm截面Q355E钢锻件,可选择820~840 ℃正火处理,以获得优良稳定的低温冲击吸收能量。     

基于分区减光的电弧增材制造熔敷道尺寸主被动联合视觉检测

设计了电弧增材制造熔敷道成形尺寸主被动联合视觉检测方法,以克服结构光主动视觉传感的滞后性与被动视觉传感的信息单一性. 为了实现极高亮度的熔池与极低亮度的结构光条纹在同一CCD靶面同时清晰成像,提出了分区减光策略,对熔池与结构光条纹进行差异化的减光,使二者光强在减光之后水平相当,进而清晰成像. 相机成像光路分析表明,需要将分区减光元件设置在镜头前方一倍焦距以外或镜头后方焦点与靶面之间. 该方法实现了单CCD在一幅图像中同时清晰拍摄熔池和结构光条纹. 开发了一套图像处理算法,实时提取出了熔敷道尺寸. 结果表明,熔敷道高度检测误差优于0.1 mm,宽度检测误差优于0.2 mm.     

羰基铁粉复合多孔吸波涂层的优化设计

目的 解决吸波剂羰基铁粉颗粒(CIP)构成的吸波涂层存在密度较大、涂层厚度过大的问题.方法 利用三维多孔结构降低复合吸波涂层的密度并改善阻抗失配,从而构筑轻质宽频羰基铁粉复合吸波涂层.利用有限元分析软件建立了羰基铁粉/石蜡复合多孔吸波涂层的仿真模型,通过仿真研究了三维多孔结构的孔隙率、孔径和孔隙分布方式对复合吸波涂层性能(最小反射损耗、有效吸收带宽、峰值吸收频率和密度)的影响规律,揭示了羰基铁粉多孔结构的吸波机理,并确定了具有最佳综合性能的羰基铁粉三维多孔复合吸波涂层的结构参数.结果 随着孔隙率的增加,涂层密度减小且峰值吸收频率向高频移动;而随着孔径的减小,涂层除峰值吸收频率向高频移动外,最小反射损耗和有效吸收带宽分别呈减低和增加的趋势,吸波性能得到有效改善.孔隙分布方面,在随机、有序、梯度递减和梯度递增4种分布方式中,梯度递减分布表现出最佳的吸波性能.相较于无孔结构,羰基铁粉质量分数为75％、孔隙率为16％、孔径为0.325 mm、孔隙呈梯度递减分布的三维多孔涂层,其有效吸收带宽(RL<–10 dB)拓展了49.3％(从4.10 GHz增加到6.12 GHz),密度降低了4％(从2.71 g/cm3降低到2.6 g/cm3),而最小反射损耗仅仅损失0.7％.结论 多孔结构的引入可以实现羰基铁粉涂层轻质、宽频吸波的目的.     

结构尺寸对Ti6Al4V多孔结构力学性能的影响

采用激光选区熔化技术制造了不同单元结构尺寸（1~6 mm）、孔隙率（40~80%）的拓扑优化多孔阵列结构,研究了单元结构尺寸对其压缩形变规律和弹性性能的影响。结果表明,多孔阵列结构的抗压强度、弹性模量均与单元结构尺寸成反比,抗压强度在126~199 MPa,弹性模量在3.5~55.47 GPa;压缩应力-应变曲线与单元结构尺寸有关,分别遵循弹性、弹脆性和脆性多孔材料三种应力应变规律;通过数值模拟多孔阵列结构的压缩形变过程,解释了两种45°断裂带的成因,力学性能与实验结果基本吻合;利用Gibson-Ashby模型评价多孔结构的稳定性,稳定性参数C与单元结构尺寸成反比;给出Gibson-Ashby拟合方程,特征参数n随单元结构尺寸增加而增大;建立了单元结构尺寸、相对密度和相对弹性模量的三维曲面数学模型,提出骨植入体的设计区域。     

SLM NiTi记忆合金BCC点阵结构的吸能特性研究

通过选区激光熔化（SLM）技术制备了不同体积分数的NiTi记忆合金BCC点阵结构（基于CAD及基于三周期极小曲面TPMS）,分析了失效前的压缩响应,研究了体积分数、单元构型和微观组织对能量吸收的影响。结果表明：NiTi BCC点阵（体积分数5 %~25 %）在压缩至损伤前具有优秀的比能量吸收（0.45~1.89 J/g）,卸载后加热可恢复至92 %以上;体积分数及单元构型对NiTi BCC点阵的压缩响应有重要影响;体积分数小于15 %时,CAD样品具有更长可压缩应变,比能量吸收更好;体积分数大于15 %时,TPMS样品具有更高压缩应力,比能量吸收更好;SLM过程中的阶梯效应导致了点阵支杆的下表面与内部具有不同的材料组织,下表面处熔池条纹更深更宽且晶粒更加粗大;材料异质性导致了相对较差的机械性能,不利于能量吸收;由于受载下应力集中位置及异质比例的不同,该材料异质性对低体积分数的TPMS样品的不利影响更大。     

The compressive and shear response of titanium matrix composite lattice structures

A method has been developed for fabricating millimeter cell size cellular lattice structures with square and diamond collinear truss topologies from 240 μm diameter Ti–6Al–4V-coated SiC monofilaments (titanium matrix composite (TMC) monofilaments). Lattices with relative densities in the range 10–20% were manufactured and tested in both compression and shear. Because of the very high strength of the TMC monofilaments, the compressive strengths of both topology lattices were dominated by elastic buckling of the constituent struts. However, under shear loading, some of the struts are subjected to tensile stresses and failure is then set by tensile fracture of the monofilaments. Analytical expressions are derived for the elastic moduli and strength of both lattice topologies and the predictions are compared with measurements over the range of relative densities investigated in this study. Excellent agreement between the measurements and predictions is observed. The specific shear strength of the TMC lattices is superior to all other cellular materials investigated to date, including carbon fiber-reinforced polymers (CFRP) honeycombs. Their compressive properties are comparable to CFRP honeycombs. The TMC lattices have a brittle response and undergo catastrophic failure at their peak load. They appear most promising as candidates for the cores in sandwich structures intended for elevated temperature and multifunctional applications where their limited ductility is not a significant constraint.     

3D打印轻质高强钨材的力学性能研究

采用选择性激光熔化（SLM）3D打印方式成功设计和制造了具有点阵结构的钨材，结合有限元分析、扫描电镜、准静态单轴压缩试验探究了不同点阵结构下钨材力学性能的变化规律，分析了微观组织对力学性能的影响。结果表明圆弧型点阵结构可有效降低节点处的应力集中，保持点阵结构轻质、低孔隙率特性同时还维持着钨材的高强度力学性能，平均抗压强度达到535MPa，平均质量仅为1.25g，激光打印后圆弧点阵较立方点阵平均抗压强度提升93%，其中体心圆弧点阵（BCA）显示出更优抗压性能，极限抗压强度达到721MPa，结构致密度为理论值12.8%；力学性能指标接近于变形态。与立方点阵相比，圆弧点阵具有良好的能力吸收特性，后者相较前者总能量吸收值提升223%，圆弧点阵平均能量吸收达到1664J/cm3。此外，SEM图像显示圆弧点阵因其弧形特性，减少了打印中斜支柱的悬挂距离，成型效果优于立方点阵。     

Evaluation of light-weight AlSi10Mg periodic cellular lattice structures fabricated via direct metal laser sintering

Aluminium alloy porous structures are highly demanded for many applications such as light-weight aerospace and heat exchanger products. Conventional manufacturing methods such as casting, however, faces difficulty in making aluminium alloy complex periodic cellular lattice structures with designed unit cell shape and size and volume fraction. This study evaluates the manufacturability and performance of AlSi10Mg periodic cellular lattice structures fabricated via direct metal laser sintering (DMLS). Various lattice structures at different volume fractions and unit cell sizes are designed by repeating a unit cell type called “diamond”. Due to the self-supported feature of the diamond unit cell, low volume fraction (7.5–15%) AlSi10Mg periodic cellular lattice structures can be fabricated by the DMLS process with the unit cell sizes ranging from 3 mm to 7 mm. A good geometric agreement is found between the original design structure models and the DMLS made structures, but the strut sizes of the DMLS made structures are slightly higher than the designed values and thus pore sizes decrease. There is clear relationship between the compressive modulus and strength of the structures and their volume fraction and unit size. Hence, this study shows that light-weight aluminium structures can be designed and made with the controlled unit size and volume fraction and the predicted mechanical properties.     

Deformation stabilization of lattice structures via foam addition

Stochastic foams are soft but absorb energy efficiently under compressive loading; in contrast, periodic lattice structures are strong but generally exhibit poor energy-absorbing characteristics. Here we present and assess a hierarchical composite concept that aims to combine the desirable attributes of stochastic foams and lattice structures. The composite comprises a low-density polymer lattice structure with centimeter-scale voids and stochastic foam with pores in the sub-millimeter scale in the spaces between the lattice struts. The assessment is made on the basis of compressive response. We show that the post-yielding strength of the lattice can be doubled with the addition of even a weak (low-density) foam: the strength exceeds the combined contributions from the lattice structure and the foam alone. Addition of slightly denser foams can lead to an even larger strength increase. Using X-ray computed tomography, we show that the strength elevation is attributable to the stabilization of the strut members against buckling when surrounded by foam. Finite-element calculations of lattice structures alone and lattice/foam composites show similar characteristics. This composite concept may allow attainment of combinations of strength and energy absorption capacity that cannot be accessed by either foams or lattice structures alone.     

Compressive properties and energy absorption characteristics of open-cell nickel foams

Open-cell nickel foams with different relative densities and pre-stretching degrees were subjected to room temperature quasi-static compressive tests to explore their compressive properties. The compressive properties of the nickel foams including yield strength, elastic modulus, energy absorption density and energy absorption efficiency were calculated accurately. The results show that the compressive properties of yield strength, elastic modulus and energy absorption density increase with the increase of relative density of nickel foams. The compressive properties are sensitive to the pre-stretching degree, and the values of yield strength, elastic modulus and energy absorption density decrease with the increase of pre-stretching degree. However, the energy absorption efficiency at the densification strain state exhibits the independence of relative density and pre-stretching degree. The value of energy absorption efficiency reaches its peak when the strain is at the end of the collapse plateau region.