Effect of a Transverse Tensile Stress on the Electric-Field-Induced Domain Reorientation in Soft PZT: In Situ XRD Study

The effect of a transverse tensile stress on the electric-field-induced 90°-domain reorientation in tetragonal lead zirconate titanate (PZT) near the morphotropic phase boundary was investigated in situ using X-ray diffraction (XRD). The XRD intensity ratio, I ₍₀₀₂₎/ I ₍₂₀₀₎, which represents the ratio of the volume of the c -domains to that of the a -domains on the PZT surface, was examined as a function of the electric field at various stress levels. It was found that a transverse tensile stress changes the electric-field dependence of I ₍₀₀₂₎/ I ₍₂₀₀₎, especially at higher electric fields. Without a transverse tensile stress, I ₍₀₀₂₎/ I ₍₂₀₀₎ began to saturate at E ≈ 800 kV/m. With a transverse tensile stress of 75 MPa, I ₍₀₀₂₎/ I ₍₂₀₀₎ increased with an upward curvature with the electric field, indicating that the transverse tensile stress enhanced the field-induced 90°-domain reorientation, and increased the effective piezoelectric coefficients at larger electric fields. At E = 900 kV/m, the estimated d _31,domain changed from −200 × 10⁻¹² V/m at zero stress, to −350 × 10⁻¹² V/m at 75 MPa.     

不同软硬段含量的聚醚酯纤维结构与性能的关系

为了说明聚醚酯纤维的形态结构与性能的对应关系,选择不同软硬段含量的聚醚酯切片进行熔融纺丝试验。结果发现:随着硬段含量的增加,纤维的断裂强度增大,但回弹性降低;当硬段质量分数为65%时,纤维的断裂强度为1.12 cN/dtex,而回弹性降至50%左右。通过广角X射线散射、小角X射线散射以及双折射、声速取向等试验进一步分析了不同软硬段含量的聚醚酯纤维的形态结构变化,发现在硬段含量高的聚醚酯纤维内部有利于形成较高的取向结构,有助于纤维强度的提升;然而,此时纤维内形成较小尺寸的结晶结构分散于无定形区内,相分离程度低,致使其回弹性降低。     

Effect of Interphase Structure on the Debonding of Polycarbonate from S-2 Glass Fibers

The effect of interphase structure on the debonding of polycarbonate from S-2 glass fibers has been studied. The shear strength, fracture toughness and hydrolyic stability of the interphases were measured in a single fiber composite of a continuous S-2 glass fiber embedded in a polycarbonate matrix. Polycarbonate oligomers were chemically grafted onto the glass fiber surfaces through use of a silicon tetrachloride intermediary and the properties of the resulting interphases were compared with those of two commercial sizings and ozone-cleaned surfaces. Evaluation was accomplished by measuring the stress transmission across the interphase, τ, by carrying the embedded single fiber fragmentation test to saturation and by using computer simulations and a finite element analysis to calculate the strain energy release rate, G, of the observed fiber-matrix debonding accompanying the first fiber fracture. The oligomer-grafted interphase exhibited improved stress transmissibility and toughness, after 24 hours in boiling water. The tenacity of the tightly bound oligomers was confirmed via DRIFT, TGA and GC/MS experiments on Soxhlet-extracted fibers.

The grafting reaction was modeled on a high surface area silica and studied using solid state NMR to determine reasons for the greater stability of the oligomer-treated surfaces. Measurements of chemical shifts and spin-lattice relaxation times indicate that the oligomers are chemically attached to the surfaces, providing for a well bonded, water resistant interphase. Parallel experiments on a monomeric Bisphenol A-primed silica surface provided evidence that chemical bonding was primarily responsible for the greater hydrolytic stability.     

Effect of Interphase Structure on the Debonding of Polycarbonate from S-2 Glass Fibers

The effect of interphase structure on the debonding of polycarbonate from S-2 glass fibers has been studied. The shear strength, fracture toughness and hydrolyic stability of the interphases were measured in a single fiber composite of a continuous S-2 glass fiber embedded in a polycarbonate matrix. Polycarbonate oligomers were chemically grafted onto the glass fiber surfaces through use of a silicon tetrachloride intermediary and the properties of the resulting interphases were compared with those of two commercial sizings and ozone-cleaned surfaces. Evaluation was accomplished by measuring the stress transmission across the interphase, τ, by carrying the embedded single fiber fragmentation test to saturation and by using computer simulations and a finite element analysis to calculate the strain energy release rate, G, of the observed fiber-matrix debonding accompanying the first fiber fracture. The oligomer-grafted interphase exhibited improved stress transmissibility and toughness, after 24 hours in boiling water. The tenacity of the tightly bound oligomers was confirmed via DRIFT, TGA and GC/MS experiments on Soxhlet-extracted fibers.

The grafting reaction was modeled on a high surface area silica and studied using solid state NMR to determine reasons for the greater stability of the oligomer-treated surfaces. Measurements of chemical shifts and spin-lattice relaxation times indicate that the oligomers are chemically attached to the surfaces, providing for a well bonded, water resistant interphase. Parallel experiments on a monomeric Bisphenol A-primed silica surface provided evidence that chemical bonding was primarily responsible for the greater hydrolytic stability.     

承压设备上的轴向应力对开孔补强的控制

大部分规范的开孔补强计算都是基于压力载荷(内压,外压,或者最大压差)作用下,最大应力方向所需要的缺失面积,但设备实际所承受的载荷不仅仅是压力载荷。通过对几种典型设备的分析来说明:在某些工况下,非压力载荷对开孔补强计算是有控制作用的。     

Effect of various organic fibers on the stiffness,strength and impact resistance of polypropylene; a comparison

Composites were prepared from a polypropylene homopolymer and four types of organic fibers, wood, flax, poly(ethylene terephthalate) (PET) and poly(vinyl alcohol) (PVA). Mechanical properties were studied by tensile and impact testing, and structure by scanning electron microscopy. Local deformation processes were followed by acoustic emission testing. Composite strength changes in a wide range and depends on coupling. The deformability of the composites also varies considerably, more plastic deformation occurring in composites prepared with the PET and PVA fibers. Compared to traditional stiff fibers, fracture resistance can be improved significantly with PET and PVA fibers; impact strength as large as 30 kJ m^–2 can be achieved with PVA. © 2020 The Authors. Polymer International published by John Wiley & Sons Ltd on behalf of Society of Industrial Chemistry.     

热力管道应力分析及实例应用

指出了对热力管道进行应力分析的重要性。阐述了应力分析的目的、原则、主要内容及其安全评定。由于管道应力分析技术高,一般工程人员难以完成。因此提出了热力管道应力分析的一般模型。结合实例,应用CAESARⅡ软件对热力管道进行应力计算。对应力分析过程中可能遇到的问题进行了归纳,并对解决这些问题的方法进行了讨论。     

Effect of Residual Surface Stress on the Strenght Distribution of Brittle Materials

The introduction of residual surface stresses into a material can change the strength distribution simply due to variability in the stress intensity factor of surface cracks. This variability arises from the distribution in surface (critical) crack lengths. A fracture mechanics approach was used to determine the influence of surface compression on the average strength and the standard deviation of the strength distribution. The strengths of the stress-free samples were assumed to fit a twoparameter Weibull distribution, and the increases in strength resulting from the surface compression were determined using fracture mechanics. It was determined from the analysis that the standard deviation/average strength ratio (coefficient of variation) initially increases, passes through a maximum, and ultimately reaches a plateau value below the initial value, as one increases the depth of surface compression. The maximum increase in the strength scatter occurs when the depth of the surface compression is approximately equal to the characteristic crack size. These changes were found to be dependent on the magnitude of the surface stress, as well as the characteristic strength, Weibull modulus, and fracture toughness of the stress-free material.     

整体浇注钢包烘烤过程中内衬温度场和应力场分析

采用数值分析方法研究整体浇注钢包烘烤过程中内衬温度随时间变化情况,得出内衬各点温度随时间变化特征及不同点处温度分布,并通过现场测试验证模型结果正确性.采用有限元方法对烘包某一时间点内衬应力分析,探讨烘烤过程中整体浇注钢包应力分布集中情况及原因,为提高整体浇注钢包使用寿命提供一定的指导作用.     

熔体静电纺丝中电极结构对电场和纤维的影响

采用Ansys数值模拟方法,建立了电场分析的有限元模型,研究了电极结构不同时的电场分布及其对纤维直径的影响,以及电压大小对纤维直径的影响。并进行了实验对照分析,发现电极结构包括圆板电极和圆环电极影响熔体静电纺丝的电场分布,但场强最大都出现在喷嘴处,并随接收距离的增大成不同趋势减小,但中空电极能集聚电场,稳定场强,获得更细的纤维。     

某杀爆弹装药弹体残余应力分布的有限元分析

为研究装药弹体残余应力对杀爆弹使用安全性的影响,分析了装药过程的应力-应变特征。假设药柱的应力分布不涉及压制过程炸药的应力-应变历史,采用两种方法对装药弹体在静载荷下的应力进行分析计算,一种是将整个弹体划分成较小的网格进行求解,另一种是先对整个弹体进行网格划分,然后根据求解的需要对局部网格进行加密。两种计算结果相差不大,应力主要集中在扩爆孔底部,最大为1.907×1-0 3M Pa,与同等压药密度成型药柱的屈服极限8.67 M Pa相差甚远。在应力作用下,局部所产生的最大变形为2.71×1-0 9m,可以恢复。     

基于小波-神经网络的瓷坯泥内部应力分布的软测量

针对真空练泥机中可塑性坯泥的颗粒定向问题,研究真空练泥机机头内壁压力对坯泥内部应力的影响,同时使用小波-神经网络获得真空练泥机机头内壁压力和泥料内部应力之间的对应关系,并利用此关系实现坯泥内部应力分布的在线软测量.研究表明:采用小波.神经网络可以精确地得到真空练泥机机头内壁压力和坯泥内部应力的函数关系,并在此基础上完成坯泥内部应力分布的在线软测量.     

定应力和拉伸速率对复合固体推进剂反复拉伸试验的影响

为了获得交变应力作用下推进剂的疲劳性能参数,利用材料试验机对推进剂试件进行了反复拉伸试验,考察了定应力和拉伸速率对推进剂疲劳破坏的影响.结果表明,当拉伸速率一定时,推进剂试件所受的定应力越大,其循环破坏次数越少,而且应力水平和循环破坏次数的自然对数符合指数函数关系;当应力不变时,拉伸速率越快推进剂试件越容易发生破坏.试...     

Effect of Oxidation on Single-Fiber Pullout Interfacial Shear Stresses in a Silicon Carbide–Borosilicate Glass System

The debonding, τ_d, and frictional, τ_f, interfacial shear strengths between 140-μm diameter SiC (with a 1-μm C-rich coating in which SiC particles are embedded) monofilaments and borosilicate glass were measured using the single-fiber pullout method as a function of postfabrication heat treatments [5 h at temperatures between 200° and 525°C] in 4% H₂–96% Ar and air. The debonding shear stress remained virtually unchanged after extended H₂ anneals. In air, however, τ_d, was found to initially increase and then subsequently decrease with increasing postfabrication heat treatment temperature. The initial increase in τ_d is due to enhanced bonding between the fiber and the borosilicate matrix as a result of the oxidation of the SiC particles embedded in the outermost carbon layer coating. At temperatures greater than about 450°C, oxidation of the C layer results in the severe degradation of the interfacial shear strengths.     

十溴二苯乙烷协同芳纶纤维增强阻燃聚丙烯复合材料的性能研究

以十溴二苯乙烷三氧化二锑（DBDPE Sb2O3,D S）为阻燃剂,芳纶纤维（AF）为增强材料,制备了阻燃增强PP复合材料,同时研究了AF和D S对PP复合材料力学、阻燃、热稳定性能和断面形貌的影响。结果表明,PP/AF/D S的拉伸强度、弯曲强度和缺口冲击强度较PP分别提高了41 %、48 %和117 %,垂直燃烧达V 0级。此外,AF和D S在提高残炭量和热稳定性及降低热释放量方面都表现出良好的协同效应,而AF体现出较好的抗融滴作用。     

Effect of Plasma Treatment on the Adhesion of Carbon Fibers to Thermoplastic Polymers

A study has been made of the effect of RF plasmas on the adhesion of carbon fibers to polycarbonate and polysulfone. Treatment in oxygen plasma significantly increased the adhesion to both polymers. The effect is lost if the treated fiber is stored in air for a week. Surface analysis using XPS indicated an increase in atom percent oxygen but the spectra were unchanged for the stored fibers even though there had been a significant loss in adhesion. It is suggested that oxygen surface functionality is responsible for the improved adhesion but that this surface activation is lost on storage. Due to a sampling depth of 5-10 nm, XPS would not be expected to detect this small change in surface functionality.     

Effect of Plasma Treatment on the Adhesion of Carbon Fibers to Thermoplastic Polymers

A study has been made of the effect of RF plasmas on the adhesion of carbon fibers to polycarbonate and polysulfone. Treatment in oxygen plasma significantly increased the adhesion to both polymers. The effect is lost if the treated fiber is stored in air for a week. Surface analysis using XPS indicated an increase in atom percent oxygen but the spectra were unchanged for the stored fibers even though there had been a significant loss in adhesion. It is suggested that oxygen surface functionality is responsible for the improved adhesion but that this surface activation is lost on storage. Due to a sampling depth of 5-10 nm, XPS would not be expected to detect this small change in surface functionality.     

An Interphase with Changing Properties and the Mechanism of Deformation in Particulate-Filled Polymers

The comparison of the results of calculations based on experimental data with those derived from a simple, two phase, elastic model proved the existence of a hard interphase in particulate-filled composites. Moreover, beside elastic properties, also other mechanical characteristics of the interphase, including yield stress, are different from those of the components. An energy analysis showed that the relationship between the yield stress of the matrix and the debonding stress determines the mechanism of deformation. Strong adhesion leads to matrix yielding, while decreased interaction leads to debonding, with a corresponding dependence of composite yield stress on filler content. Particle size, interaction and interphase properties determine the stress necessary to separate the matrix/filler interface. The thickness of the interphase depends on the strength of the interaction; a linear correlation was found between the size of the interlayer and the reversible work of adhesion.     

复合催化剂中有机硅组分在粘胶基碳纤维制备中的作用

催化剂是制备粘胶基碳纤维的关键技术之一,通过热质联用(TG-MS)、扫描电镜(SEM)和力学性能测试等手段分析了硫酸铵/氯化铵/有机硅复合催化剂体系中有机硅对粘胶纤维热裂解的影响。结果表明:有机硅不具备无机催化剂所具有的使粘胶纤维的热解反应变得缓和,提高热解反应的收率,促进粘胶纤维热裂解过程中H2O、CO和CO2的生成等作用。其作用主要是在浸渍过程中促进无机催化剂向粘胶纤维内部渗透,同时还能使粘胶纤维大分子发生适度的交联,提高其在中温碳化过程中的可拉伸性,最终提高粘胶基碳纤维的性能。     

Effect of Blend Ratio and Draw Ratio on the Mechanical Properties of PET/PP Blended Conjugate Fibers

This study analyzes the influence of blend ratio and draw ratio on the fiber properties of blend fibers composed of poly (ethylene terephthalate), or PET, and polypropylene, or PP, (hereafter referred to as PET/PP conjugate fibers). For a comparison, PET and poly (butylene terephthalate), or PBT blends, (hereafter referred to as PET/PBT conjugate fibers) are also investigated. Various blend ratios of fibers are melt spun and drawn in a multistep drawing method. The conjugate fibers are evaluated using tenacity, Young's modulus, wide-angle X-ray diffraction, differential scanning calorimetry (DSC), and scanning electron microscopy (SEM) tests. The results show that multistep drawing using a lower first-step draw ratio provides a higher tenacity and Young's modulus. Furthermore, when the blend ratio is 75/25 in a PET/PP conjugate fiber and 50/50 in a PET/PBT conjugate fiber, the polymer components undergo a phase inversion phenomenon. A PP sub-micron (10^?1 ～ 10⁰ micron) fiber of about 0.0001 ～ 0.00017 tex in fineness, or about 0.4 ～ 0.5 micron in diameter, can be obtained when PET/PP conjugate fiber is treated with a 25% NaOH aqueous solution by weight. However, A PBT sub-micron fiber cannot be achieved using a PET/PBT conjugate fiber.