粉煤灰漂珠/聚氨酯复合泡沫铝材料压缩性能与本构关系研究

采用压力渗透法制备出了铝基复合泡沫材料,填充材料是以粉煤灰漂珠为主要组分、硬质聚氨酯泡沫为粘结剂的复合泡沫材料.通过准静态实验和分离式霍普金森压杆(Split Hopkinson pressure bar,SHPB)动态压缩的方法研究了复合泡沫铝的压缩力学响应,然后建立了动态本构关系.研究表明,复合泡沫铝的压缩应力-应变曲线与其它泡沫材料的应力-应变曲线类似,文中的两种铝基复合泡沫具有应变率效应,复合泡沫铝较密度相近未填充前的泡沫铝基具有更高的压缩强度与能量吸收能力.但由于漂珠尺寸的不同,导致两种复合泡沫铝的动态压缩结果不尽相同,且小颗粒复合泡沫铝在动态冲击下吸能效果最好.在本研究实验的应变率和密度范围内,本文建立的本构模型曲线与实验曲线吻合较好.     

纸浆模塑材料压缩力学行为及其本构关系的研究

对纸浆模塑材料的压缩力学行为进行较系统的实验研究,结果表明材料密度和应变率都对其力学性能有一定的影响.随着材料密度的增加,其弹性模量和强度极限都有增加的趋势.随着应变率的增加,其材料的弹性模量有减小的趋势,而强度极限有所增大.利用描述泡沫塑料的经验型本构关系框架,给出一种经验型的纸浆模塑材料本构模型,根据不同密度材料在不同应变率下的压缩实验数据对该模型中的有关系数进行拟合.验证结果表明,提出的本构方程能在一定应变率范围内反映材料的应力-应变关系.     

硬质聚氨酯泡沫动态压缩本构模型研究及有限元仿真

硬质聚氨酯泡沫常被用于缓冲吸能结构,为了更好地在动态加载场景中对该材料进行设计及仿真,需要对其动态力学性能及本构模型进行研究。文章对硬质聚氨酯泡沫进行中低应变率下的动态压缩试验,并进一步分析了应变率对材料性能的影响;使用Avalle模型建立了描述材料压缩力学行为的本构模型,在模型中引入应变率项并基于试验数据的量化分析结果对模型进行了修正;在ABAQUS有限元软件中输入修正后的Avalle本构模型数据,对硬质聚氨酯泡沫进行冲击仿真。研究结果表明：硬质聚氨酯泡沫应力-应变响应对应变率具有敏感性,修正后的Avalle模型对多种应变率下的试验数据拟合较好,而基于该模型进行的有限元数值仿真在6 m/s及8 m/s的冲击条件下加速度峰值与试验数据误差分别为4.09%以及12.72%,模型可靠性较高。     

动态冲击载荷下无氧铜的力学性能研究

利用分离式Hopkinson压杆实验装置(SHPB)对无氧铜进行了常温下不同应变率(2 500 s-1~15 500 s-1)的动态力学性能进行了测试,得到常温下无氧铜的真实应力-真实应变曲线,并分别通过Power-Law本构模型和JohnsonCook本构模型对其进行了拟合。结果表明:无氧铜在受到动态压缩载荷的作用时,其塑性流动应力对应变率并没有表现出敏感的趋势,但对于材料的屈服应力则在应变率高于14 000 s-1时明显增加,同时材料的应变强化效果降低,另外,相较于Johnson-Cook本构模型,Power-Law本构模型能够更准确的预测无氧铜在高应变率下的塑性流动应力。     

球形孔泡沫纯铝的静态力学性能

在获得球形孔泡沫纯铝压缩应力-应变曲线基础上,研究了泡沫纯铝的压缩屈服强度、吸能能力.结果表明:球形孔泡沫纯铝与球形孔泡沫铝合金的压缩应力-应变曲线相似,分为三个部分:线弹性阶段、平台阶段和密实阶段;球形孔泡沫纯铝相对于球形孔泡沫铝合金是一种吸能能力更强、韧性更好的新材料;采用Gibson-Ashby模型来分析球形孔泡沫纯铝的压缩屈服强度,吻合良好.     

混合型泡孔结构硅橡胶泡沫的制备与压缩性能

采用化学发泡的方法制备了开孔-闭孔混合型泡孔结构的硅橡胶泡沫材料,研究了密度对硅橡胶泡沫压缩性能的影响。结果表明:随着材料密度的增加,相同应变所对应的应力增大,应力-应变曲线明显上移,ε_(0.32)随着密度增加而减小,拟合的线性方程为ε_(0.32)=-101.008ρ+84.286,相关系数R=-0.998;压缩应力松弛率随着密度增加而线性增大。     

泡沫铝芯体冲击力学性能试验研究

基于马歇特落锤实验原理，设计与开发出具备测试与数据采集分析功能的高过载冲击试验系统，并运用该设备研究了反复冲击条件下泡沫铝芯体的耐冲击能力和应力-应变响应特性、吸能特性与反复冲击次数的敏感性。实验结果表明：泡沫铝芯体的动态应力应变曲线也具有泡沫材料的应力应变曲线的“三阶段”特征，泡沫铝芯体具有更高的良好的缓冲吸能特性，且该特性随着泡沫铝芯体细长比的增加而增强。     

泡沫铝材料参数反求及其填充锥形薄壁管的吸能性能研究

为了研究一种商业化生产的泡沫铝力学性能并对其填充结构进行仿真模拟,基于材料的准静态压缩试验和材料本构模型进行了泡沫铝和铝合金材料参数反求,并采用试验数据验证了所得材料参数的正确性。运用有限元软件LS-DYNA进行数值分析,研究了壁厚、锥角和填充泡沫铝密度等设计参数对泡沫铝填充锥形薄壁管吸能特性的影响。结果表明,利用材料反求的方法可获得准确的材料参数;泡沫铝密度和壁厚对平均力的影响更为显著,相比于锥角更易控制能量吸收;管壁厚度是影响初始峰值力的主要因素;填充泡沫铝后不仅能够改善薄壁管的变形情况、增大比吸能,且对初始峰值力的影响较小。     

高强石墨材料的动态本构模型

利用分离式Hopkinson压杆试验装置对SMF-800高强石墨进行了冲击压缩试验,获得了不同应变速率(618,868,1 185s-1)下的应力-应变曲线;采用损伤型朱-王-唐粘弹性本构模型和一维弹脆性损伤本构模型分别对应力-应变曲线进行拟合,并对拟合结果进行了对比。结果表明:高强石墨材料的破坏应力和应变随着应变速率的增大而不断增大;损伤型朱-王-唐粘弹性本构模型比一维弹脆性本构模型更能有效描述高强石墨材料的动态力学性能,在应变速率为618,868,1 185s-1时,前者拟合曲线的相关指数分别为0.992 15,0.999 52,0.972 15。     

细晶T2纯铜动态力学性能及本构模型

晶粒大小是影响多晶金属材料力学性能的重要因素之一,研究细晶T2纯铜在高温、高应变率下的动态力学性能并建立其本构模型对切削加工有着重要意义。通过电子力能测试仪进行T2纯铜试样准静态压缩试验,并利用霍普金森压杆装置完成了不同应变率和不同温度的动态压缩试验。试验结果表明,纯铜材料具有明显的应变强化效应和温度软化效应,其动态压缩下的强度高于准静态压缩,但在高应变率区域内,并无明显的应变率强化效应。基于Johnson-Cook本构模型得到了细晶T2纯铜本构方程参数,拟合曲线与试验结果吻合较好。     

闭孔泡沫铝力学特性及其在汽车碰撞吸能中的应用研究进展

汽车低能耗、安全和轻量化已经成为汽车领域研究的热点问题,闭孔泡沫铝作为一种轻质吸能金属材料,在低密度下具有良好的比刚度和比强度,同时具有良好的抗冲击性和能量吸收性,已逐渐引起汽车产业界地重视。简述泡沫铝单轴压缩试验中弹性模量、抗压强度、屈服强度、平台应力、致密化应变等参数的定义和试验标准;综述闭孔泡沫铝的本构方程的研究现状,重点讨论屈服面模型;总结泡沫铝的微观结构有限元建模方法,比较商业软件中集成的宏观材料模型。归纳吸能材料的特点,分析闭孔泡沫铝的吸能能力和抗冲击能力;综述应变率和冲击速度对泡沫铝吸能特性有无影响的研究进展,并对可能存在的影响进行解释。总结闭孔泡沫铝在汽车轻量化和碰撞安全性领域的应用,具体分析典型的案例。指出当前闭孔泡沫铝的力学特性及其在汽车结构中应用存在的问题与难点,总结并提出本研究领域可以借鉴的研究方向。     

A new hardening rule for metallic foam plasticity

Metallic foams are a class of porous materials widely used in the industry because of their advantages. In recent years, extensive studies on the behavior of these materials have been conducted. Several constitutive equations have also been presented and applied. This study proposes a new constitutive equation that predicts metallic foam behavior using the stress–strain curve in uniaxial compression. The proposed model offers a new functionality for work hardening and is evaluated for both isotropic and combined hardening. The constitutive equations are implemented in MATLAB and integrated using return mapping algorithm. The material parameters are identified using genetic algorithm and through a comparison of the experimental and numerical results. The aluminum foams discussed in this paper are the commercially available types, Foaminal and Alporas. The comparison of numerical and experimental results indicate that this new constitutive equation predicts foam behavior in a reasonable manner. Moreover, a good agreement is observed between the experimental and computational curves.     

A constitutive model for polyurethane foam with strain rate sensitivity

The present work investigates the strain rate dependent behavior of polyurethane foams and formulates a new constitutive model in order to improve the fit of the experimental data at various strain rates. The model has seven parameters that are decided by quasi-static compression tests at two strain rates. Two models for low and high density polyurethane foams are shown to give stress strain relation at various strain rates. Dynamic compression tests were carried out to give stress strain data at high strain rate and the results are compared with those of the constitutive model.     

Measurement of strain rate sensitivity of aluminium foams for energy dissipation

In this paper the structural performance of aluminium alloy foams have been investigated under both static and dynamic compression loads. Three foam typologies (M-PORE, CYMAT, SCHUNK) in a wide range of density (from 0.14 to 0.75 g/cm³), made by means of different process-routes (melt gas injection, powder metallurgy, investment casting) have been analysed. Foams microstructural characterization has been carried out through morphometric measurements by means of Scanning Electron Microscopy (SEM) and Computed Tomography (CT) and subsequent digital image processing in order to determine average cells size and cell distributions on different section planes. The experimental study aims to assess the strain rate sensitivity and energy absorption capability of commercially available metal foams and to point out the correlation between the mechanical behaviour and the physical and geometrical properties of the foam. It has been found that the specific energy dissipation of foams with similar density can be quite different: for the same volume of foam, average values of 1770, 1780 and 5590 J/kg at 50% nominal compression have been measured on M-PORE (0.19 g/cm³), CYMAT (0.28 g/cm³) and SCHUNK (0.28 g/cm³) foams, respectively. Impact tests showed that the dependence of the plateau stress on strain rate could be considered negligible for M-PORE and CYMAT foams while it is quite remarkable for SCHUNK foams. Moreover, it was found that the peak stress of CYMAT foams has a quite large sensitivity on the loading rate.     

硬质聚氨酯泡沫在多轴压缩试验下的力学特性研究

硬质聚氨酯泡沫广泛应用于吸能装置。为研究硬质聚氨酯泡沫在多轴载荷下的力学响应,应用静水压试验和围压试验对其进行多轴压缩试验,分析其力学特性和吸能特性。结果表明：在静水压试验中,泡沫材料经历了弹性区域、平台区域和密实化区域三个阶段,相应的体积弹性模量、平台应力和单位体积吸能量均比单轴压缩试验的高;而在围压试验中,泡沫仅经历弹性阶段和峰值后阶段,无明显的平台区域和密实化区域。峰值偏应力随着围压增加而减少,但当围压超过一临界值时,偏应力-轴向应变曲线表现出一定的随机性,丧失了进一步承受轴向载荷的能力。基于试验数据和微分硬化屈服面模型,获得不同塑性应变下硬质聚氨酯泡沫的屈服面。     

泡沫铝结构对其拉伸力学性能的影响

研究了开孔与闭孔两种胞孔结构的泡沫铝在不同相对密度下的准静态拉伸力学性能,并与单向压缩性能进行了对比.结果表明：开孔和闭孔泡沫铝的拉伸曲线由线弹性变形段和塑性变形段组成,线弹性变形段很短,塑性屈服中没有出现明显的屈服点;高密度的开孔泡沫铝的杨氏模量、抗拉强度较低密度的闭孔泡沫铝要大;随着相对密度的增大,两种结构泡沫铝的力学性能均明显增强,符合Gibson和Ashby关系式,泡沫铝在准静态下的抗拉强度比抗压强度略低,而拉伸杨氏模量比压缩杨氏模量大得多.     

A general constitutive relation for linear elastic foams

A three-dimensional linear elastic constitutive relation is formulated based on a representative unit cell of foam using elasticity theory and micromechanics homogenization scheme. The displacement and strain fields of the unit cell are obtained from elasticity theory and used to derive the macroscopic strain field defined on the outer surface of unit cell through homogenization scheme. By assuming a uniform macroscopic stress on the unit cell surface and the existence of strain energy potential, the constitutive relation of linear elastic foams is obtained. The newly derived constitutive relation is a function of mechanical property of solid constituent, the geometry of cell struts, and the porosity of foams and is able to characterize the anisotropic behavior of foams due to non-uniform strut geometry. The linear elastic response of open-celled foams with both low- and medium-relative densities can be studied using the derived constitutive relation. The effective elastic modulus for uniform strut geometry is reduced from the constitutive relation and agrees well with Gibson and Ashby's semi-empirical equation, Warren and Kraynik's, and Zhu's analytical models within relative density ranging from 0 to 0.35. For non-uniform strut geometry, the calculated effective elastic moduli in three axial directions are different and the material displays anisotropic behavior. The bulk modulus shows less dependence on the variation of the strut geometry. Poisson's ratios are also reduced from the compliance matrix.     

A novel approach to the manufacturing and experimental investigation of closed-cell Al foams

This investigation proposes a modified technique for manufacturing closed-cell aluminum (Al) foams to reduce the cost of the foaming agents during the casting and foaming processes. The addition of foaming agents promotes the uniformity of cell sizes and controls the viscosity of the melting aluminum alloy. This work elucidates the mechanical characteristics of closed-cell aluminum foams under compressive loading. The discussions in this paper cover the compressive stress–strain curve and the densification strain and energy absorption effects of various specimens with various porosities. The thermal conductivity of the aluminum foams is determined, and the results are compared with some theoretical predictions. The optimum parameters for meeting some practical design requirements, such as impact absorption and thermal insulation design applications, are discussed. Finally, an empirical correlation between the normalized yield strength and the relative densities is obtained.     

碳化硅增强泡沫铝层合圆管的制备及力学性能研究

用熔体发泡法制备了碳化硅颗粒增强泡沫铝样品，分析了碳化硅增强泡沫铝在准静态压缩条件下的变形行为。用不锈钢圆管为面板，碳化硅颗粒增强泡沫铝为夹芯制备层合圆管，研究了层合圆管在准静态压缩条件下的变形行为和能量吸收性能。研究表明：碳化硅颗粒增强泡沫铝的屈服强度在5～12MPa之间，对泡沫铝材料的力学性能有明显的增强作用；层合圆管在保持泡沫铝轻质、高吸能效率的同时，大幅度提高了吸能能力；碳化硅增强泡沫铝层合圆管的压缩屈服应力达到45MPa，平台应力达到40MPa，具有优良的吸能性能。