Micromechanics of residual stress and texture development due to poling in polycrystalline ferroelectric ceramics

This paper presents micromechanics based analysis of elastic strain and changes in the texture of poled polycrystalline ferroelectric PZT ceramics for direct comparison with synchrotron X-ray measurements. The grains are modelled as spherical inclusions, to which transformation strains are assigned depending on the fractions of different ferroelectric domains. Eshelby's inclusion problem with the classical self-consistent method is applied to evaluate the elastic state of the grains. In particular, the elongation due to lattice elastic strain is calculated as a function of inclination Ψ relative to the polar axis. The ratio of diffraction peak intensities, corresponding to the domain fractions, is also expressed as a function of Ψ. This analysis identifies the special character of the reflection, for which the lattice strain along in the stress free state is independent of ferroelectric domain population and hence unaffected by poling. The elongation due to the lattice strain parallel to and peak intensity ratio are expressed in terms of the overall macroscopic strain of a poled specimen, each having a dependence.     

载荷对Al2O3增强Y-TZP陶瓷磨损特性的影响

采用往复式摩擦磨损试验机研究了10%(质量分数计)Al2O3增强四方氧化锆多晶Y-TZP陶瓷材料(简称10ADZ)在不同载荷下的磨损行为与机制.结果表明:随着载荷的增加和滑动时间的延长,10ADZ陶瓷的磨损率增大,但并非呈线性增加,磨损率增长幅度不同;在62 N低载荷条件下,10ADZ陶瓷的磨损机制以犁沟和塑性变形为主;在124 N载荷下其主要的磨损形式为塑性变形、微切削和微断裂;而在310 N的高载荷下其主要的磨损机制为断裂磨损.     

氮化硅陶瓷平板振动模态参数的研究

本文采用压电陶瓷片测振技术,试验分析了氮化硅陶瓷平板的固有频率及模态阻尼比,试验结果与有限元计算结果比较吻合。本文还对氮化硅陶瓷平板与普通钢平板做了对比试验,结果表明氮化硅陶瓷平板的固有频率及模态阻尼比都较高。     

纳米-Al2O3陶瓷粉末的预热爆炸压实实验研究

对纳米-Al2O3陶瓷粉末在预热温度为0.5Tm的条件下,以不同的爆炸压实压力实施了烧结实验。通过X射线衍射分析了烧结体的晶型,并用高分辨率扫描电子显微镜进行了微观组织观察。实验结果表明,纳米-Al2O3陶瓷粉末在爆炸压力为13.1 GPa时可得到晶粒间结合致密且晶粒度在100 nm左右的-Al2O3烧结体;而在爆炸冲击压力为9.35 GPa以下时,烧结体的晶型没有发生转变,仍然是-Al2O3晶型。     

非均匀铁弹畴变对离面极化压电陶瓷应力强度因子的影响研究

基于文献中报道的试验结果，本文考虑非均匀的畴变过程区，它包含一个位于中心的饱和区和环绕饱和区的渐变区．为了描述外加应力引起的部分铁弹畴变，本文采用一个显式的基于最小能量原理的非均匀畴变准则．考虑离面极化的压电陶瓷，假设其初始极化矢量平行于离面方向．畴变后的电畴位于面内，具体方位由最大释放功来确定．基于非均匀畴变准则，本文给出了裂尖处非均匀畴变区几何及畴变体积分数的分布．并在静止裂纹和稳态扩展裂纹两种特殊情况下计算了铁弹畴变对裂尖处应力强度因子的影响．结果表明：(1) 静止裂纹尖端处的畴变减小了材料的起裂强度；(2) 准静态稳态裂纹附近的畴变增加了材料的断裂强度．且理论预测的R曲线渐近值与试验结果定量吻合．     

Review on underwater sound absorption materials and mechanisms

随着我国加速实施海洋强国战略,对先进水下吸声材料的需求日益迫切.与空气吸声不同,水下的高静水压力和复杂的海洋环境对水下吸声材料提出了更为苛刻的要求.吸声问题的本质是如何将弹性能高效地转化为热能或其他形式能量.本文综述了主要以聚合物分子内摩擦机制及界面耗能机制为基础的传统水下吸声材料.传统水下吸声材料面临的主要是其在低频及高静水压力下吸声性能差的问题.这是因为：一方面受质量密度定律的限制,有限厚度的水下吸声材料无法有效吸收水中传来的低频声波;另一方面,在高静水压力下,弹性材料如高分子聚合物会变“硬”,从而大大降低了声波弹性能的转换效率.随着局域共振理论及超材料概念的提出,发展出了一系列新型水下吸声材料,为解决水下吸声材料遇到的难题提供了新思路.局域共振理论的特点是可以用小尺度结构控制长波声波的传播,从而可以解决低频吸声问题.本文重点综述了局域共振理论,以及由此发展出的声子木堆、声子玻璃等新型水下吸声材料.声子玻璃材料在局域共振理论基础上,通过引入多孔金属骨架结构提高了材料的抗压性能,从而解决了高静水压力下材料吸声性能变差的问题.本文最后对水下吸声材料未来发展方向进行了展望.     

爆炸成型弹丸对Al2O3装甲陶瓷材料的侵彻实验研究

用爆炸成型弹丸(explosively formed projectile, EFP)对Al2O3装甲陶瓷材料进行了侵彻（depth of penetration, DOP）实验,得到了99Al2O3装甲陶瓷对模拟EFP的质量防护因数和差分防护因数及他们随陶瓷块厚度的变化规律,初步评估了99Al2O3装甲陶瓷对EFP的抗侵彻性能,解释了装甲陶瓷对EFP的抗侵彻过程和机理。研究结果表明,增加约束可以提高陶瓷的抗侵彻性能。     

陶瓷人工关节的跑合和摩擦性能研究

研究３种生物陶瓷材料（氧化铝，氮化硅和碳化硅）在水中的跑合及其摩擦特性。结果表明：跑合前，氮化硅－氮化硅摩擦副的起始摩擦因数和稳态摩擦因数最高，碳化硅－碳化硅磨擦副的起始摩擦因数和稳态摩擦因数最低，跑合后，氧化铝－氧化铝摩擦副的稳态摩擦因数最高，碳化硅－碳化硅摩擦副的起始摩擦因数和稳态摩擦因数仍然最低。当摩擦副表面均加工到超光洁状态（表面粗糙度Ｒａ为纳米数量级）时，碳化硅－碳化硅摩擦副的摩擦性能最     

Al2O3陶瓷复合靶抗长杆弹侵彻性能和机理实验研究

用DOP(depthofpenetration)实验研究了质量分数为 90 %的Al2 O3 陶瓷复合靶抗长杆弹侵彻性能。实验表明 :随陶瓷厚度的增加 ,以差分效益系数和靶平均阻力表征的陶瓷复合靶的抗长杆弹侵彻性能降低 ;盖板能增强陶瓷复合靶抗侵彻性能。对回收陶瓷和盖板的破坏特征分析表明 :长杆弹对陶瓷复合靶侵彻过程大致可分为初期侵彻和稳定侵彻两个阶段 ,但对薄靶和厚靶 ,两个阶段在整个侵彻过程中所占比重不同。     

The effect of impurities on the viscoelastic response of polycarbonate reinforced with short glass fibers

Observations are reported in oscillatory torsion tests at room temperature on unfilled and fiber-reinforced polycarbonates melt-blended with impurities (acronitrile–butadiene–styrene, high-impact polystyrene, low-density polyethylene, poly(ethylene terephthalate) and Nylon 6,6). Constitutive equations are derived for the viscoelastic behavior of glassy polymers. With reference to the theory of cooperative relaxation, a polymer is treated as an ensemble of meso-regions with arbitrary shapes and sizes. The time-dependent response of the ensemble is attributed to rearrangement of meso-domains. The rearrangement events occur at random times, when meso-regions are excited by thermal fluctuations. Stress–strain relations are derived by using the laws of thermodynamics. The governing equations are determined by four adjustable parameters that are found by fitting the experimental data. Fair agreement is demonstrated between the observations and the results of numerical simulation. The study focuses on the effects of the concentration of impurities and glass fibers on material parameters.