平板玻璃钢化有限元数值模拟

用非线性有限元分析方法,建立了玻璃的热粘弹性应力松弛数学模型、Narayanaswamy结构松弛数学模型以及热边界模型,对平板玻璃钢化过程进行三维仿真模拟,得到玻璃中心和边界区域的温度与应力的变化历史及分布.为优化设计平板玻璃钢化参数提供了依据,能缩短产品开发周期、降低成本并保证产品质量.     

采用热辐射和热交换对残余应力进行预测和控制

在实验室和工厂进行热钢化平板玻璃生产时,多采用单射流和多射流对成型了的玻璃进行冷却。首先,应该考虑到辐射的转移和残余应力对玻璃的最后部分的影响。三维流体动力学计算模型（计算流体力学）的研发,帮助我们对气体的流动进行分析,并确定钢化过程当中玻璃表层的热交换情况。然后,将结构和应力松弛引入三维有限元模型中进一步进行分析,采用光弹性测量的方法对钢化玻璃表面及周边范围内的残余应力进行测量,这个数值可以对玻璃的钢化厚度进行验证。通过在多射流的设备中进行的分析中发现,温度分布和残余应力都是均匀分布的。最后,采用超声波的新方法来对钢化的残余应力进行测量。采用这种方法进行单射流对钢化玻璃进行冷却实验,得到的实验结果与预测数值相一致。     

支撑柱缺位对弧面钢化真空玻璃支撑应力的影响

根据弹性力学、柱壳理论及数学微分法建立了弧面钢化真空玻璃力学模型,基于ANSYS有限元数值分析模拟,分析了3 mm厚弧面钢化玻璃基板不同部位支撑柱缺位对弧面钢化真空玻璃的支撑应力和弯曲变形的影响.研究结果表明,支撑柱缺位对其周围支撑应力影响较大.在中间和角落部位,当支撑柱连续缺位数量超过2个,最大应力为117.77 MPa,最大变形量为0.566 mm;在边缘部位,当支撑柱连续缺位数量超过3个,最大应力为96.183 MPa,最大变形量为0.217 mm,均超过安全允许范围.该研究对弧面钢化真空玻璃的质量检测具有指导意义.     

钢化真空玻璃在温差作用下的变形特征

钢化真空玻璃两侧存在温差是导致其弯曲失效的重要原因之一。通过钢化真空玻璃温差变形试验和数值模拟,得到不同尺寸的钢化真空玻璃(5+0.5V+5)在不同温差下的变形特征。结果表明:钢化真空玻璃受两侧温差形成的球面弯曲曲率半径与钢化玻璃基片的厚度成正比,与钢化玻璃基片的线膨胀系数及两侧温差成反比;钢化真空玻璃的变形量与钢化玻璃基片尺寸、温差大小及曲率半径呈正相关;同一温差下钢化真空玻璃变形量随长边尺寸增大而增大;数值模拟结果与试验结果吻合,相对误差在5%以内,能够为不同尺寸钢化真空玻璃在温差下的变形预测提供参考。     

支撑点间距对钢化真空玻璃力学特性的影响

钢化真空玻璃中支撑点间距对玻璃的力学性能产生重要影响,因此支撑点合理间距的选择尤为关键.本文通过建立钢化真空玻璃的力学模型,对支撑点正方形排列时间距对钢化玻璃的力学性能影响进行了数值分析,研究结果表明:钢化玻璃的变形量和最大Mises应力随着支撑点间距增大而增大.对于厚度为5 mm钢化真空玻璃,支撑点间距不大于7 cm时,均能满足钢化真空玻璃的力学性能.钢化真空玻璃支撑点间距为7 cm时,不仅满足其力学性能,还大大减少了支撑点数目.此研究将为钢化真空玻璃制造中支撑点间距的选取提供理论依据.     

玻璃钢化季节性调压数值模拟

建立了风栅中玻璃的冷却模型,数值模拟玻璃冷却的温度和应力变化规律,反演了不同季节风温时的合理匹配风压。结果表明,在玻璃淬冷过程,约3 s时玻璃表面拉应力达到最大,若该应力大于玻璃此时的抗拉强度,玻璃将破裂。此后玻璃从外到内降温速率逐渐减小,在约15~17 s时玻璃表层受内部影响减弱,表面应力趋于稳定。与钢化玻璃表面应力测试结果相比,数值模拟结果略小,但相对误差不超过5%。随冷却风温降低,玻璃钢化所需的风压逐渐减小。在玻璃钢化程度接近的情况下,风压随风温降低近似线性减小,钢化风压调节量与环境温度变化量的相关系数为0.103 kPa/K。     

浮法玻璃成型过程的数值模拟

建立了浮法成型过程的数学模型,并用三维有限元方法,模拟了5mm浮法玻璃成型过程,分析了拉边机在浮法玻璃成型中的作用以及拉制过程中玻璃的应力、位移、厚度分布。在玻璃拉制过程中,x方向应力主要集中在机头后区域;y方向应力主要集中在机头和玻璃带接触的地方;x方向应力沿玻璃板宽度方向分布,且范围较广;发现了实验中存在的速度“穿越”现象。模拟结果与实验结果的比较表明,建立的数学模型很好地模拟了浮法玻璃成型过程。     

熔盐成分对高铝玻璃化学钢化性能的影响

在不同成分的熔盐内对高铝玻璃以不同的时间及温度进行了化学钢化处理,测试对比了样品的钢化应力及离子交换深度。结果表明:钢化应力在温度较低时随钢化时间呈先增后减趋势,温度较高时随钢化时间呈对数衰减趋势;离子交换深度在相同时间下随温度提高而增大,在同一温度下随钢化时间呈对数增长趋势;添加高熔点钾盐对提升钢化应力明显提升,在一定范围内钢化应力与添加量呈正相关,应力增幅在温度较低时体现明显;氢氧化钾的使用能明显提升钢化效果,且在温度较低时效果更佳。     

手机玻璃面板化学钢化若干问题的探讨

阐述了手机玻璃面板对化学钢化后玻璃性质的要求,如表面压应力、应力层深度、硬度等指标,还指出高铝高镁玻璃成分比较适合化学钢化,同时还探讨了二步和三步离子交換法在手机玻璃上的应用。     

风冷钢化玻璃的自然破损

1玻璃的钢化方法 玻璃的钢化方法有两种,一个是将玻璃板加热到600℃以上,然后通过风冷使表面产生压缩应力的风冷钢化;另一个是用离子半径较大的钾（K）离子置换玻璃表面含有的钠离子（Na）的化学钢化。建筑物及车辆使用的钢化玻璃多为前者。     

Stress and Volume Relaxation in Annealing Flat Glass

Laboratory simulation of the industrial process of annealing sheet glass has yielded data on the genesis of stresses in initially stress-free glass. The experimental results differed from expectations based on classical annealing theory in that stresses began to develop in the annealing range even when the glass was being cooled at a constant rate, i.e. even in the absence of any changes of temperature gradients within the glass. Typically, these stresses account for 40% of the total residual stress in glass annealed according to a linear schedule. The remaining 60% are the well-known thermoelastic stresses that arise later in the annealing process from the decay of temperature gradients in the glass. The stresses observed to arise in glass as it is being cooled at a constant rate are attributed to volume relaxation effects which, in parts of the annealing range, generate stresses rapidly enough that they are not dissipated by stress relaxation. A mathematical model of annealing is proposed that takes account of both stress and structural relaxation. The model fits the experimentally observed evolution of stresses during linear cooling. It also suggests that (with the activation energies of stress and structural relaxation about the same) the actual rate, at any given temperature, of structural relaxation is about 4 times lower than that of stress relaxation.     

Volume Relaxation Far from Equilibrium

Narayanaswamy's model of structural relaxation is applied to the data of Hara and Suetoshi on volume relaxation in plate glass. Both the Adam-Gibbs and Arrhenius equations are used to represent the relaxation time. Equally good fits are obtained with both equations, but only the Adam-Gibbs model gives Physically meaningful fitting parameters. The exponent b describing the shape of the relaxation time spectrum decreases at small values of reduced time, as it does for stress relaxation Discrepancies between calculated and measured densities at 350°C are not resolved by allowing for a nonlinear driving force or thermorheological complexity.     

Modeling birefringence in SiO2 glass fiber using surface stress relaxation

The retardance of silica glass fibers was evaluated using photoelastic techniques. Here, surface birefringence in glass fibers is shown to be a consequence of surface stress relaxation for as-received fibers drawn from Suprasil II. The surface features of the birefringent fibers were compared to a model of the residual axial stress profile resulting from a diffusion-controlled surface stress relaxation. Additionally, a uniform birefringence in the fiber equivalent to a constant tensile stress was recognized and attributed to structural anisotropy produced during fiber drawing. The contribution of structural anisotropy to the observed birefringence remained constant as the surface features were successively etched away. Surface compressive stress generation was also observed, as retardance corresponding to a surface compressive stress was found to increase with applied tensile stress during short heat treatments. Significant features of the retardance profile in as-received silica glass fibers, with a thin surface compressive stress layer and compensating interior tensile stress, agreed with the residual stress profiles predicted by the surface stress relaxation model after correcting for this observed structural anisotropy.     

陶瓷支撑柱表面形貌对真空平板玻璃应力分布的影响

利用电测法分析了不同表面形貌的陶瓷支撑柱对真空平板玻璃应力分布的影响,试验结果表明,各种真空玻璃的最大应力均发生在四角第二个支撑处,得出了支撑柱与和玻璃的接触面积量对玻璃应力分布会产生影响的结论。用有限元法分析各种真空玻璃的应力应变场,得出了各种真空玻璃在封边处、支撑处、支撑柱之间的连线中点处等重要部位的应力分布。控制支撑高度误差和玻璃的平整度,保证受力的均匀,可增加真空玻璃的强度,增加其可靠性,提高使用寿命。     

Stress and Structural Relaxation in Tempering Glass

Temper stresses are brought about, primarily, by a partial relaxation of transient stresses generated by rapid cooling of the glass. Stress relaxation under nonisothermal conditions is competently handled by a mathematical tempering model, in which glass is treated as a simple viscoelastic material. However, this model proved inadequate in some respects since the properties of glass depend not only on its instantaneous temperature but also on its prior thermal history. A tempering model was therefore developed that incorporates both stress and structural relaxation. Predictions of this structural model are compared with experimental data on tempering and contrasted with predictions of the viscoelastic model. Such comparisons revealed that, typically, structural relaxation accounts for approximately 24% of the total residual temper stresses.     

Time calculation for the after-cure cooling process of the cast modified double base propellant in a large rocket motor

An unsteady heat conduction model is proposed to calculate the temperature distribution of the case-bonded rocket motors and the time required for the cooling process based on the experimentally determined thermal and mechanical parameters of a cast modified double base propellant (CMDB) and its glass steel shell. The resultant value of the time is then used to derive the corresponding stress relaxation modulus, which is compared with the modulus data obtained from uniaxial tensile stress relaxation experiments to see if the internal stress has been thoroughly relaxed within this period of time.     

Structural Relaxation Time of Bulk and Fiber Silica Glass as a Function of Fictive Temperature and Holding Temperature

The structural relaxation times of silica glass, both bulk glass and fiber glass at various fictive temperatures, were estimated at selected temperatures. The structural relaxation time of a glass is needed to estimate the rate of change of various glass properties in the glass transition temperature range. Traditionally, the Tool–Narayanaswamy model, in which activation energy of the relaxation time is divided into two parts, one representing the fictive temperature effect and the other representing the temperature effect, has been used. The model can explain the property changes of glass in the glass transition temperature range well when the change of the fictive temperature is small, but the model fails when the change of the fictive temperature is large, as was the case when a fiber sample was heat treated close to the glass transition temperature. The structural relaxation times estimated in the present work exhibited activation energies that varied with fictive temperature, unlike the assumption in the Tool–Narayanaswamy model. On the other hand, the relaxation time for both bulk glass and fiber glass exhibited the same temperature and fictive temperature dependence within experimental error. From these observations, one can see the source of discrepancy between the Tool–Narayanaswamy model and experimental data when the change in fictive temperature is large.     

Dielectric investigation of molecular dynamics of blends: III. Effect of molecular weight in TMPC/PS blends

Dielectric and calorimetric measurements have been carried out for tetramethyl polycarbonate/polystyrene (TMPC/PS) blends with different compositions. The effect of varying the molecular weight of the weakly polar component (PS) on the molecular dynamics of the polar segments of TMPC has been thoroughly studied over wide ranges of frequency (10⁻²−10⁵ Hz), temperature (50–220°C) and number average molecular weight, M̄_n, (6500–560 000 g mol⁻¹). All blends were found to be compatible regardless of the composition ratio and the molecular weight of PS. Some new and interesting experimental findings have been observed concerning the effect of molecular weight on the glass temperature and on the broadness of the glass transition and relaxation. Neither the kinetics nor the distribution of relaxation times of the local process observed in pure TMPC was affected by blending with PS, regardless of the composition ratio or the molecular weight of PS. It has been concluded that the mixing of the polymeric components to form a homogeneous single phase (compatible blend) does not take place on a segmental level but on a structural one. The size of this structural level has been suggested to have the same volume as the cooperative dipoles, which is assumed to be the minimum volume responsible for a uniform glass transition (10–15 nm). The molecular weight dependence of the relaxation characteristics of the glass process and temperature could be attributed to the variation in the size and packing of the structural units.