基于能量平衡方法的压痕尺寸效应分析

针对硬度测试中出现的压痕尺寸效应现象,采用纳米压痕技术与原子力显微技术相结合,得到压痕过程中的载荷与压深加载卸载曲线和压痕三维图,从中可以得到压痕过程中压头所做的塑性功、最大压深、塑性变形面积、塑性变形体积等,并以此为变量提出了一个基于能量平衡方法的改进模型,此模型能更好地解释压痕尺寸效应.单晶硅实验结果表明:在较大压深下,由于形成新表面所消耗的功是出现压痕尺寸效应的主要因素;随着压痕深度的减小,用于克服材料对压头的阻力而消耗的功所起的作用越来越大;而在更小的压深下,用于产生塑性变形的初始能量和测试系统误差所造成的影响会越来越大,不可忽视.     

注塑工艺对管件专用PE100级聚乙烯TUB121N3000M收缩率的影响

通过正交试验法,研究了注射压力、保压压力、注射速度、加工温度、模具温度对管件专用PE100级聚乙烯TUB121N3000M收缩率的影响。结果表明:注射压力和保压压力的增加会提高TUB121N3000M的结晶度及收缩率;注射速度和加工温度过大或过小会减小制品的收缩率;模具温度越高,制品的热收缩量和结晶度越大,收缩率越高;模具温度对TUB121N300M制品的收缩率影响最明显。     

纳米压痕硬度尺寸效应的残余面积最大压深模型

针对材料在纳米压痕硬度测试实验中出现的压痕尺寸效应,通过对单晶硅的纳米压痕实验,得到压痕的真实最大压深,再利用原子力显微镜获得压痕的三维形貌,并结合Matlab软件得到压痕的真实残余面积。以残余面积和最大压深为变量,提出了一种新的描述硬度压痕尺寸效应的模型——残余面积最大压深模型,此模型能更好地描述和理解纳米压痕硬度的尺寸效应。     

加工工艺对聚乙烯热收缩膜性能的影响

以低密度聚乙烯(LDPE)、线型低密度聚乙烯(LLDPE)和高密度聚乙烯(HDPE)为原料,采用吹塑成型法制备了热收缩膜。研究了原料配方、模具吹胀比、吹膜机牵伸比、挤出温度和膜泡冷却时间等因素对聚乙烯热收缩膜力学性能和透明度的影响。结果表明:与加入HDPE相比,配方中加入LLDPE的原料所生产的热收缩膜的综合性能较好;随着机组运行牵伸比的增大,PE热收缩膜的拉伸性能、收缩率和透光率均呈上升趋势;随着模具吹胀比的增大,PE热收缩膜的纵向收缩率下降,横向收缩率和透光率均上升;随着挤出机工艺温度的升高,PE热收缩膜的纵、横向收缩率同时上升;随着膜泡冷却时间的延长,PE热收缩膜的纵、横向收缩率和透光率均下降。     

基于正交试验的空调面板翘曲变形工艺参数优化

以影响空调面板的3个工艺参数——熔体温度、模具温度及保压压力为设计变量,翘曲变形量为目标函数,利用正交试验,选用3因素5水平进行试验方案设计,利用Moldflow软件对各方案进行有限元分析,得到最佳工艺参数组合为:熔体温度270℃、模具温度60℃、保压压力70 MPa。结果表明,在最佳工艺参数组合下,空调面板的最大翘曲变形量由优化前的2.667 mm减少到1.032 mm。将最佳工艺参数组合应用于实际生产,产品的翘曲变形得到显著改善。     

卷对卷UV压印生产厚度优化研究

在卷对卷UV压印产品生产中,为了得到优秀的厚度UV胶压印产品,对UV压印时的压料轮压力,压印车速,UV胶温度和模具辊温度的调整进行实验。通过测试产品厚度,研究生产条件对产品性能的影响。研究结果表明:压料轮的压力,压印车速,UV胶温度及模具辊的温度均对厚度有影响,只有在综合四项条件的情况下才能得到希望的厚度产品。     

基于正交试验的瓶盖注塑成型数值模拟及工艺优化

以正交试验设计为手段,借助有限元分析平台Moldflow,对某瓶盖注塑成型工艺进行数值模拟。通过分析塑件的工艺性,创建了产品的有限元模型,以最小翘曲变形量为试验指标,分析熔体温度、注射时间、模具温度、保压压力和保压时间对产品质量的影响规律。结果表明:当熔体温度为220℃、模具温度为100℃、注射时间为1.10 s、保压压力为100 MPa、保压时间为7.5 s时,所得产品的翘曲变形量最小,为0.369 9 mm,比初始模拟结果降低了34.77%,为实际注塑成型参数的设置提供了科学的理论指导。     

硅橡胶改性EVA热熔胶的制备及其性能研究

探究了不同种类蜡与乙烯-醋酸乙烯酯共聚物(EVA)热熔胶体系相容性差异,确定了选用PE蜡进行后续试验。通过熔融共混法制备了一系列不同质量分数硅橡胶改性EVA基热熔胶。对于软化点而言,添加适量的硅橡胶能提高热熔胶体系的软化点,当w(硅橡胶)=15%(相对于基体EVA总质量而言),此时硅橡胶改性后热熔胶相较于未改性前热熔胶的软化点由70℃提升到75℃。热熔胶的力学性能显示,硅橡胶对提升体系的力学性能影响不大,热熔胶体系的拉伸强度和断裂伸长率随硅橡胶添加量的增加而下降。剥离性能显示,硅橡胶的添加在高温50℃和低温0℃环境下,存在最佳添加量20%;而常温25℃下,硅橡胶的添加对其剥离性能影响不大。经硅橡胶改性后EVA热熔胶的耐热性及粘接性能均有显著提升。     

基于压痕功法对单晶硅压痕硬度的测量

在对材料的微/纳米级表层压痕硬度测试中,压痕周围出现的凸起对硬度的计算结果有很大的影响.采用压痕功法,通过载荷-压深曲线直接得到压痕过程中所作的功,利用原子力显微镜和Matlab软件,精确得到压痕中产生的塑性变形体积,并计算得到材料的硬度值.用压痕功法对单晶硅的压痕硬度进行了实验研究,并与其它方法进行了比较分析.结果表明:压痕功法得到的结果更稳定,凸起对结果影响较小.     

碳纤维/环氧界面相准静态纳米压痕表征方法分析

界面相作为纤维与树脂之间载荷传递的桥梁,其性质对整体复合材料力学性能和耐环境性能有直接影响。本研究用准静态纳米压痕技术对碳纤维T300/环氧E51体系的界面相模量进行测试分析。研究发现,当探针压入深度大于30nm以后,试样表面粗糙度对测试结果的影响可以忽略;同时,三种测试排点方式下的纳米压痕结果表明:纤维增强效应对载荷-压深曲线影响很大,由于压深和压痕间距较大,对于界面相宽度较小的碳纤维环氧复合材料体系,采用准静态纳米压痕技术不易得到其界面相的模量。     

Identification of residual stress layers at glass surfaces via crack terminating angles

Cracks terminating at free surfaces are affected by local stresses in the surface region. Under residual compression the crack front must retard compared with the crack contour in the absence of stresses. This effect can be used for an identification of residual stresses at glass surfaces. For an illustration of the procedure, Vickers indentation tests in soda‐lime glass are considered. Specimens treated by ion exchange and chemically toughening showed reduced terminating angles compared with untreated glass.     

应用压痕断裂力学分析陶瓷材料的磨削加工

应用压痕断裂力学分析陶瓷材料的磨削加工过程,根据陶瓷材料的脆性指数确定临界磨削力,分别建立了磨削主应力极值与泊松比和磨削分力比之间的回归方程,此简单函数便于计算最大磨削主应力和分析磨削裂纹.脆性指数和泊松比反映陶瓷材料的磨削加工性,磨削方式影响陶瓷材料的去除,通过陶瓷磨削实验证明分析结果.研究结果为陶瓷材料磨削参数的选择和磨削方式的确定提供了理论依据.     

黏弹材料动态纳米压入过程的尺度效应

提出柔度因子分析法表征压入尺寸效应（ISE)通讨聚甲基丙烯酸甲酯(PMMA)及热塑性聚氨酯(TPU)的动态纳米压痕试验,探讨黏弹材料动态压入过程中的压入尺度效应及其影响因素。结果表明,Berkovich针尖对黏弹材料进行纳米压痕动态测试时,主载荷是压入尺度效应产生与否的决定因素,频率对此影响较小,谐振载荷控制方式影响甚微;测试材料存在一临界值,当压入深度大于其临界值时,动态纳米压痕测试获得的黏弹材料参数与传统的动态力学分析(DMA)试验结果基本一致。     

Glass with hydration-induced compressive stress profiles

A novel potassium phospho-aluminosilicate composition is described that can be strengthened by water vapor to achieve deep compressive stress (CS) profiles. Water vapor treatment at (A) 85°C and 85% relative humidity for 40 days results in a CS of 389 ± 20 MPa and a compressive depth of layer (DOL) of 18 ± 2 μm. When treated at (B) 160°C and 0.1 MPa for 7 days, a CS of 245 ± 20 MPa and a DOL of 40 ± 2 μm is achieved. Glasses with hydration-induced stress profiles can provide high retained strength following flaw introduction compared with ion-exchanged soda-lime silicate glass. Sample treatment B also has an exemplary Vickers indentation cracking threshold value greater than 20 kgf. The hydration profile determined by secondary ion mass spectrometry (SIMS) is shown to closely match the stress profile for these samples. SIMS analysis also shows that the depth of water enrichment correlates well with the depletion depth of phosphorus. The high tendency towards water-induced strengthening for this new type of glass even enables self-strengthening by the generation of a near-surface CS profile following exposure to ambient conditions.     

Knoop Microhardness Anisotropy and the Indentation Size Effect on the Basal Plane of Single-Crystal Alumina (Sapphire)

The Knoop microhardness anisotropy profile was determined for the basal plane of a Czochralski grown alumina single crystal for indentation test loads from 100 through 1000 g. Microhardness maxima occur at low indentation test loads for the long axis of the Knoop indenter parallel to the 〈2[Onemacr][Onemacr]0〉. Minima exist for the long axis parallel to the 〈10[Onemacr]0〉. This low indentation test load profile is attributed to slip on the primary slip system, the (0001)〈[Onemacr][Onemacr]20〉, as previously noted by Brookes and co-workers. The degree of the microhardness anisotropy decreases for higher indentation test loads. This results from the activation of multiple slip systems to accommodate the greater amounts of plastic flow required by the larger indentation sizes. The microhardness profile becomes more uniform with increasing indentation test load until the Knoop microhardness approaches a test-load-independent, orientation-independent microhardness of 1167 ± 34 kg/mm². The indentation size effect (ISE) was further investigated through lubricated indentation hardness measurements. Lubrication of the test specimen surface significantly reduces the ISE. Results indicate that friction between the test specimen surface and the indenter facets is a major portion of the ISE.     

Shrinkage Behavior of Knoop Indentations in Silica and Soda–Lime–Silica Glasses

The annealing characteristics of Knoop-indented silica and soda–lime–silica glasses were investigated. These glasses were indented using a Knoop indenter in water, and they were annealed at various temperatures below the glass transition temperature. The major diagonal length of the Knoop indentation was measured before and after annealing, and the change of the diagonal length was determined. The change of diagonal length in silica glass was much larger than that in soda–lime–silica glass. This was attributed to the occurrence of more densification around the Knoop indentation in the silica glass. The activation energy of the shrinkage of the Knoop indentation in the silica glass, estimated from the temperature dependence of the relaxation time, was 46 kJ/mol, which was much less than that of viscous flow in silica glass. This suggested that the shrinkage of the Knoop indentation was caused by the structural relaxation of densified glass around the Knoop indentation.     

Contact-Damage Behavior of Textured and Random Alumina Ceramics under Hertzian Indentation

Two alumina ceramics with different microstructures were prepared by tailoring the processing conditions. In one of them, elongated alumina grains were aligned parallel to each other ("textured" material), whereas in the other, the elongated grains were uniformly distributed ("random" material). Hertzian indentation was performed on these two materials. The results showed that, although both materials exhibited a diffuse damage zone rather than typical cone cracks, the extent of damage in the textured material is significantly less than that in the random material. The difference in damage behavior between these two materials was interpreted with the aid of the contact-stress field. A new microstructural design method for improving contact-damage resistance is suggested, based on the present results.     

In Situ Cube-Corner Indentation of Soda–Lime Glass and Fused Silica

Indentation fracture with a cube-corner diamond pyramid on soda–lime silicate glass and fused silica is investigated during the entire indentation cycle in both silicone oil and ambient-air environments. Radial cracks form immediately on loading in all cases. The two-component, elastic-contact + elastic-plastic mismatch (residual) stress field model that has been used successfully to describe radial crack evolution at Vickers indentations fails to describe the fracture response with the cube-corner. The amplitudes of both elastic-contact and residual stress-intensity factors as deduced from these cube-corner experiments are up to a factor of 10 greater than have been previously observed.     

Role of Internal Friction in Indentation Damage in a Mica-Containing Glass-Ceramic

The indentation response of a mica-containing glass-ceramic that exhibits shear-driven yield in an indentation test is interpreted in terms of events occurring on the microstructural scale. It is proposed that shear-driven damage within the specimen occurs via internal sliding along cleavage planes within the mica platelets. The sliding surfaces in this case are considered to be atomically smooth so the real and apparent areas of contact coincide. The frictional shear stress is thus independent of the normal forces arising from thermal mismatch stresses and only depends on the work of adhesion of the interface and the scale of the contacts. The scale of contacts for these materials lies within an intermediate zone in which the frictional shear stress arises from the stress required to nucleate dislocation-like discontinuities within the material. This leads to a size effect similar to that experienced by a crack in Mode II loading and is in accordance with previous work in which a connection between such a size effect and the macroscopic response of the material was identified. This work has particular relevance to the design and manufacturing of ceramics in machining, wear, bearings, and coatings applications.     

Indentation-Induced Amorphization in Mullite Single Crystals

Hardness indentations with a Vickers pyramid under a load as low as 0.1 N applied at room temperature induce amorphization in single-crystal mullite when applied to the (001) crystallographic face. Different zones of damage were identified via TEM. Directly under the indenter, in the region of high-compressive stress, mullite becomes amorphous. Further out toward the matrix material, there exists a region of high plastic deformation in the form of dislocation networks, radial microcracks, and bend contours. The Vickers-induced damage is comparable to that produced by dynamic shock or intense ball milling of mullite.