安全型真空玻璃构件功能一体化优化设计

为满足建筑用安全型真空玻璃构件的开发及工程应用推广之需要,研究了真空玻璃结构优化设计所涉及的力学基础理论。根据真空玻璃构件结构特点,建立力学模型,分析了真空玻璃构件在大气压作用下支撑应力分布特征及计算公式。结果表明:大气压作用下真空玻璃构件最大弯曲拉应力分布在支撑部位玻璃外表面处,当支撑力超过其临界载荷时,会导致接触点附近玻璃锥形裂纹的产生;根据均强度理论,得到了玻璃基片在不产生压痕下支撑物的最大临界支撑力计算公式;给出了持久应力作用下真空玻璃基片的强度设计值,其中钢化玻璃的为44.40MPa,普通浮法玻璃的为8.19MPa。综合真空玻璃构件应力分布特征及传热机理,优化了真空玻璃构件设计,使其达到最佳"热学与力学"配置。     

测定陶瓷材料断裂韧性的压痕弯曲梁法的改进

考虑残余应力对压痕弯曲梁应力场强度的贡献后,对相应的K_(IC)表达式进行了修正。研究表明:在合适的压痕压制荷载范围内,弯曲梁强度σ_r与压痕裂纹深度的倒数平方根(1/a)~(1/2)之间存在线性关系;压痕处的残余应力效应可以用σ_(?)-(1/a)~(1/2)直线关系式中的强度修正项加以描述。高温下强度修正项的值随温度的升高而减小,说明残余应力在高温作用下得到了部分消除;退火处理也导致了强度修正项的减小。采用强度修正项后的K_(IC)计算公式,压痕弯曲梁法可望应用于各种温度下的K_(IC)测试;由σ_(?)(1/a)~(1/2)直线斜率求得的K_(IC)值不受残余应力影响。     

玻璃微裂强度评价

本文在分析Vickers压痕周因应力分布的基础上,提出了抗压屈服强度、表面微裂强度、弹性模量和压痕断裂韧度的计算公式,介绍了测试压痕变形量的方法。强度和模量是通过测定微米级的微裂纹和压痕附近的损伤区(小于100μm)的尺寸而计算得到的,因此称为微强度和微压弹性模量。本方法不受试件尺寸、形状及加工条件等的影响,测得的表面微裂强度和压痕断裂韧度比较真实,而弹性模量是在接近破坏时应力应变关系中测得的,因此是一个最小弹性模量。它们能反映材料的表面强度和接近破坏时的应力一应变关系,为脆性材料的强度评价提供一种新方法。     

刚性压头I型触压应力强度因子计算

平面压痕在机械性能的研究中有着广泛的应用。分析刚性压头与弹性半平面非线性触压时,发现在触压拐角处应力急剧增大有明显的应力集中现象,而且同I型裂纹有类似的应力场分布,因此可以把触压问题看成一种特殊的裂纹。分别使用了位移外推法和J积分法,求得了裂纹的应力强度因子。两种方法得到的应力强度因子相差很小,并讨论了不用材料对压痕深度的影响。     

优筋布置矩形箱体应力及变形分析

针对工业生产中矩形箱体笨重、加筋结构布置设计欠佳的问题,采用ANSYS APDL语言对矩形箱体进行静压工况下应力及变形分析。选取6因素5水平正交试验方案,以矩形箱体最大一次应力S_1max、最大等效应力S_2max以及最大变形量Δ_max作为试验指标,侧壁加强铁间距A、宽度B及厚度C,端壁加强铁间距D、宽度E及厚度F作为试验因素,结合矩阵分析法获得加强筋的优筋布置方案A₄B₅C₅D₂E₅F₂,并用ANSYS一阶优化算法对箱壁以及箱壁加强铁壁厚进行优化。结果表明:矩形箱体采用优筋布置后,箱体质量减少了27%。最后采用极限载荷分析法通过P_T=0.1 MPa试验工况验证。     

正弦波纹挡板式沉降器内流动特性

采用VOF模型对正弦波纹式入口挡板的重力非均相沉降器内流场进行数值模拟研究。对比了正弦波纹挡板与平挡板的平均流场分布情况,分析了沉降器的轴向流速均一程度（λ₁）随时间演化特性,探究了λ₁和面积加权平均湍流强度（I_a）在沉降器内空间分布特性;引入流场均稳指标USC,研究了冲击间距（L_b/D）对USC的影响。结果表明：正弦波纹挡板作为入口构件可以有效降低返混。在0.84＜L_b/D＜2.17范围内,正弦波纹板沉降器内流场的均一程度整体高于平面挡板;随着L_b/D减小,平挡板沉降器内流场的λ₁基本不变,但正弦波纹挡板沉降器内流场的λ₁降低,且对I_a的影响不明显。对比平挡板,正弦波纹挡板可以有效降低轴向速度的梯度,使返混区面积减小,流场稳定性提高。随着L_b/D增加,USC值呈现多峰值趋势,L_b/D=2.17时正弦波纹板沉降器的USC取得极大值为14.68,较平挡板提高了93.67%。     

Co2+掺杂ZnO-MgO-Al2O3-SiO2系微晶玻璃的制备及光学性能

本文采用熔融法和热处理制备了Co²⁺掺杂的ZnO-MgO-Al₂O₃-SiO₂(ZMAS)系透明微晶玻璃,基于X射线衍射的结果确定了微晶玻璃的主要晶相为ZnAl₂O₄/MgAl₂O₄,并且随着晶化处理时间的增加,微晶玻璃的物相构成没有发生明显变化,尖晶石相的结晶度和平均晶粒尺寸呈现先增大后减小的趋势。吸收光谱和发射光谱的结果表明Co²⁺进入了尖晶石相ZnAl₂O₄/MgAl₂O₄中,并取代了四面体位置(T_d)的Zn²⁺或Mg²⁺。随着晶化处理时间的增加,样品的吸收光谱强度和发射光谱强度均呈现先升高后降低的趋势,这与X射线衍射结果的变化趋势一致,说明可以通过控制微晶玻璃的结晶度来调控光学性能,这对制备性能优良的微晶玻璃材料具有一定的指导意义。对比了采用不同价态Co的氧化物原料制备的微晶玻璃,结果表明无论是掺杂CoO还是Co₂O₃,微晶玻璃尖晶石相中的Co元素均以Co²⁺形式存在。此外,将所制备的微晶玻璃材料在1 540 nm处的基态吸收截面(σ_gas)同Co掺杂的其他基体材料进行了对比,发现它有望作为可饱和吸收体应用于调Q激光器中。     

PAN链缠结的影响因素及其对PAN/DMSO溶液流变行为的影响

采用旋转流变仪对聚丙烯腈/二甲基亚砜（PAN/DMSO）溶液进行了流变学测试,探究了表观黏度（η_α）、储能模量、损耗模量、损耗正切角与温度、浓度以及剪切情况之间的关系,明确了PAN链缠结对PAN/DMSO溶液流变行为及其分子结构的影响,探究了PAN链缠结与浓度、温度及剪切速率之间的关系。结果表明,预剪切可以有效地拆除部分PAN链的缠结,使PAN/DMSO溶液η_α降低,且温度升高及浓度降低时剪切作用对η_α的影响作用减小,流变稳定性提高。     

t-ZrO2相变提高搪玻璃抗拉强度的研究

采用添加四方相氧化锆(t-ZrO₂)的方式增强搪玻璃涂层的力学性能,通过三点弯曲试验研究搪玻璃表面应变变化情况,对断裂截面进行XRD、SEM、拉曼分析。结果表明,添加适量t-ZrO₂改善了搪玻璃的表面形貌,减少了气孔数量。在三点弯曲试验中,2%t-ZrO₂质量含量的搪玻璃承受的最大力值提高了7 kN,在11 kN三点弯曲压力作用下出现裂纹,应变值提高约37%。含有t-ZrO₂搪玻璃试样的截面断裂前后发生t相到m相的相变,t-ZrO₂相与搪玻璃原始釉相的边界处出现裂纹的偏转,从而抑制裂纹扩展。     

Lightnin静态混合器内气泡分散流体动力学特性实验研究

以Lightnin静态混合器（LSM）内水-空气气液两相体系为研究对象,在连续相水表观速度U_L=0.071~0.127 m/s和离散相空气表观速度U_G=0.007~0.042 m/s的条件下,研究内径100 mm的LSM内气液两相湍流流动阻力与气泡分散水动力学行为。使用分辨率为1920×1080的高速相机Revealer-2F04M采集混合器内不同轴向窗口的气泡群演化过程。结果表明：当U_L<0.085 m/s和U_G=0.025~0.042 m/s时,LSM内的流型为泡状流。随着气泡群流经混合元件数的增加,气泡群的Sauter平均直径d₃₂逐渐减小。当液体表观速度U_L≤0.085 m/s时,Sauter平均直径d₃₂随气体表观速度的增加先减小后增大;U_G =0.028 m/s时d₃₂达到局部最小值,53%的气泡直径d_B/D₀在0.02~0.05范围内。Sauter平均直径、内径与无量纲停留时间τ之间的关系满足d₃₂/D₀=0.031τ^-0.14We^-0.41。平均气含率α的增大显著增加了单位体积内气泡数量密度,加剧气泡与元件表面碰撞频率,增大旋涡二次流强度,导致摩擦系数显著降低;采用Lockhart-Martinelli方法对实验数据回归,得到气液两相流压降预测常数C的关联式：C=5.26×10⁵U_G^-0.91/Re^0.74。     

Work of Fracture and Crack Healing in Glass

The work of fracture, γwoF, of a soda-lime-silica glass was determined as 5.5 J/m² in an inert atmosphere and 4.4 J/m² in air by using a short bar specimen with a chevron notch. The critical stress intensity factor K_IC calculated from γ_wof obtained in an inert atmosphere agreed with the value, 0.88 MN/m^3/2, determined by the indentation method. In unloading-loading cycles during stable crack growth, crack healing was observed both on the diagram of load vs load-point displacement and visually. Crack healing is more prevalent in an inert atmosphere, occurring only minimally in air. The energy for healing was measured as 0.65 J/m² in an inert atmosphere and ∼0.21 J/m² in air.     

Flat R-Curve from Stable Propagation of Indentation Cracks in Coarse-Grained Alumina

The fracture toughness of coarse-grained A1₂O₃, known for pronounced "Iong"-crack R-curve behavior, was studied in the "short"-crack regime utilizing the stable propagation of indentation cracks in bending. A combination of in situ microscopic crack growth observations and mechanical testing enabled measurement of crack extension curves. They reflect the contributions of residual indentation stress intensity and applied bending stress intensity on the total crack driving stress intensity and allow determination of the residual stress factor χ and the toughness K_R. The results indicate that χ depends on indentation load and A_R is surprisingly constant rather than increasing. To resolve the latter contradiction with long-crack R-curve behavior, combined short/long-crack fracture tests were performed with the same specimens. Starting with stable indentation crack growth and continuing with stable long-crack extension, the previous toughness results were confirmed, i.e., constant toughness from indentation cracks and increasing toughness from long cracks. The influence of crack-opening behavior on bridging-controlled R-curve toughening can qualitatively explain the observed discrepancies.     

Microhardness of SiO2 Glass in Various Environments

It was shown in earlier studies that the crack initiation stress of SiO₂ glass was stressing-time dependent only in water while it was time independent in nonaqueous liquids. In order to clarify the roles that various liquids play in the crack initiation of SiO₂ glass, Knoop microhardness measurements were made on SiO₂ glass in various liquids and FTIR spectroanalysis was performed on the indented SiO₂ glass. The microhardness measurements showed a similar loading-time dependence to the crack initiation stress. The microhardness was separated into two parts: the surface contribution and the volume contribution. The results showed that the volume (or bulk) component was a nearly constant value for glass measured in nonaqueous liquids and that it was lower for glass measured in water. Consistent with these results, FTIR analysis showed that water entered the glass during indentation while nonaqueous liquids did not. The surface component showed a good correlation with the crack initiation stress.     

Subcritical Crack Growth in Soda-Lime Glass under Combined Modes I and III Loading

Fracture and subcritical crack-growth characteristics under combined Modes I and III loading were studied using the modified compact tension (CT) specimens of soda-lime glass. The combined mode load was applied to the specimen in the direction β with respect to the initial crack. By superposition of Mode III, the advancing crack begins to rotate at an angle Ψ to the initial crack plane, which nearly maximizes the Mode I stress intensity factor K _I(Ψ), and the crack continues to propagate in the same direction. In this case, unlike combined Modes I and II, the crack breaks into multiple partial fronts, and ligamentary bridging forms fracture lances when these segmented cracks are held together. The crack velocity d a /d t was plotted versus the maximum Mode I stress intensity factor K _I(Ψ) for combined Modes I and III loading. The d a /d t values are initially high, and the crack growth tends to be discontinuous compared with the result for pure Mode I. The subcritical crack growth seems to occur when the K _I value for the initial crack reaches a certain value. The d a /d t - K _I(Ψ) curves for combined Modes I and III lie roughly on the same curve as that for pure Mode I as the crack growth increases.     

Use of Crack Branching Data for Measuring Near-Surface Residual Stresses in Tempered Glass

An analytical procedure based on fracture mechanics is used to obtain the amount of residual stress in glass from measurements on the fracture surface. The technique utilizes the measurement of microcrack branching distances, known as the mirror — mist boundary, which occur at a critical crack branching stress intensity (K _m ) value. This procedurre shows that σ _A r _m ^1/2 Y _F (θ) =σ _R r ^1/2 _m +Ψ₀, where σ _A is the applied stress, r _m is the microcrack branching radius, σ _R is the residual stress, Y _F ( θ ) is the crack-border correction factor, and Ψ₀ is a material constant based on K _m . Thus, the equation is that of a straight line with the slope equal to the magnitude of the residual stress. Data for tempered glass from the literature are used to demonstrate the applicability of the technique.     

Effect of Alcohols on Crack Propagation in Glass

The effect of straight-chain alcohols having chain lengths of 6 to 12 carbon atoms on crack propagation in glasses was studied. The test was a modification of the double-cantilever-beam technique. Plots of crack velocity vs stress intensity factor, K , were trimodal, similar to those for glass tested in N₂ gas of varying relative humidity. Crack velocities in the two regions of lowest K could be explained using a model derived by Wiederhorn for the effect of water on crack propagation and were independent of alcohol chain length. The chain length of the alcohol affected the results only in the water-independent high- K region, where crack velocity increased monotonically with decreasing chain length at a given K. There was no systematic effect of glass composition within the Na₂O-CaO-SiO₂ system, but crack velocities at a given K in a 3BaO-5SiO₂ glass were higher under all conditions than those in Na₂O-CaO-SiO₂ glasses.     

A New Low-Brittleness Glass in the Soda-Lime-Silica Glass Family

In the soda-lime-silica glass family, the effect of each constituent of the composition on the brittleness was first investigated. Vickers indentation was employed to estimate the brittleness (ratio of harness ( H ) to fracture toughness ( K _c)) by measuring the C / a ratios (where C and a are the characteristic crack and indentation diagonal lengths, respectively). It was observed that a higher silica content and a lower lime content helped to lower the brittleness. Substitution of potash and magnesia for soda and calcia, respectively, was effective in lowering the brittleness. From these results, a higher molar volume was found to be a key factor for reducing the brittleness. A new low-brittleness glass was then developed with a brittleness as low as 5.1 µm^-1/2 as compared with the brittleness of 7.1 µm^-1/2 for commercial soda-lime-silica glass. The crack initiation load ( P *), measured by the Vickers indentation method, for this new low-brittleness glass was almost 10 times as high as P * of commercial soda-lime-silica glass. The new glass shows lower hardness and higher fracture toughness than the commercial soda-lime-silica glass.     

Piezospectroscopic measurement of the stress field around an indentation crack tip in ruby using SEM cathodoluminescence

Piezospectroscopy using stress-sensitive lines in the cathodoluminescence (CL) spectrum generated in response to excitation by the electron beam of an SEM has recently been shown to be a promising technique for submicron resolution stress measurements in alumina and other ceramics. This paper develops and applies the technique by mapping the wavelength shifts of the R₁ CL line around the tip of an indentation crack in a ruby single crystal. Accounting for crystallographic anisotropy, the shifts observed were quantitatively consistent with the classical crack tip stress field for all polar angles ahead of the crack tip and indicated a crack tip stress intensity factor of 1.0 MPa m^1/2. This is significantly lower than the fracture toughness of the crack plane (4.5 MPa m^1/2), and indicates the post-indentation development of lateral cracks and slow crack growth. The spatial resolution of the stress measurements was measured as 550 nm and the effects of specimen heating by the electron beam were shown to be negligible.     

Measurement of Very Slow Crack Growth in Glass

The rate of very slow crack growth in glass is measured by inducing small, controllable changes in the direction of propagation of Hertzian cone cracks at known times. After completion of a growth sequence, the sample is sectioned to reveal the fracture surface. The stress intensity factor at each stage of crack growth is calculated by using finite-element modeling of the stresses near the crack tip. Data are presented for crack growth velocities as low as 10⁻¹⁴ m/s in soda–lime glass. These data provide strong evidence for the existence of a subcritical limit for crack growth in this material.