锯齿轧花中含棉籽棉朵模型的构建与仿真

为方便分析锯齿轧花过程中籽棉的受力状况以期提高皮棉质量,在已有的层合板棉朵模型和三维编织棉朵模型基础上,提出了一种含棉籽的棉朵模型。该模型基于实际棉朵中棉籽以及棉纤维束排列呈立体网状结构的规律,假设纤维束具有圆形截面,截面形状沿轴向保持不变,在该模型的基础上利用ANSYS Workbench对轧花过程进行了模拟,研究了不同锯齿滚筒转速和棉籽密度对轧花过程的影响。结果表明:锯齿滚筒转速越大,棉纤维受影响越剧烈,但转速过大也会损伤棉纤维,棉籽密度在580 kg/m³时锯齿轧花效果最明显;实验值与模拟值误差相对较小,说明了模型的合理性。     

贵州吨糖田甘蔗良种的筛选

为了筛选适合贵州蔗区的高产高糖甘蔗良种,本研究选取黔糖4号、ROC16、ROC22、云蔗03-45、德蔗03-83、桂糖96-211、黔蔗06-212和桂糖11号等8个甘蔗品种在贵州省荔波县、册亨县和望谟县进行种植筛选。结果表明:云蔗03-45、桂糖96-211、黔蔗06-212、德蔗03-83和黔糖4号等5个甘蔗品种产糖量均达15 t/hm~2以上,可作为黔蔗"吨糖田"的理想甘蔗良种加以推广应用。     

Comparison of irreversible deformation and yielding in microlayers of polycarbonate with poly(methylmethacrylate) and poly(styrene‐co‐acrylonitrile)

Microlayers of polycarbonate (PC) with poly(methylmethacrylate) (PMMA) or poly(styrene‐co‐acrylonitrile) (SAN) were processed with varying layer thicknesses. Adhesion between PC and PMMA was found to be an order of magnitude higher than between PC and SAN, as determined with the T‐peel method. To probe the effect of the adhesion difference on yielding and deformation of PC/PMMA and PC/SAN microlayers, the macroscopic stress–strain behavior was examined as a function of layer thickness and strain rate, and the results were interpreted in terms of the microdeformation behavior. During yielding, crazes in thick SAN layers opened up into cracks; however, PC layers drew easily because local delamination relieved constraint at the PC/SAN interface. Adhesion of PC/PMMA was too strong for delamination at the interface when PMMA crazes opened up into cracks at low strain rates. Instead, PMMA cracks tore into neighboring PC layers and initiated fracture. At higher strain rates, good adhesion produced yielding of thick PMMA layers, a phenomenon not observed with thick SAN layers. The change in microdeformation mechanism of PMMA with increasing strain rate produced a transition in the yield stress of PC/PMMA microlayers. Microlayers of both PC/SAN and PC/PMMA with thinner layers (individual layers 0.3–0.6 μm thick) exhibited improved ballistic performance compared to microlayers with thicker layers (individual layers 10–20 μm thick), which was due to cooperative yielding of both components. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 77: 1545–1557, 2000     

Tensile test of poly(vinyl chloride) filled with ground calcium carbonate particles

The fracture behavior of poly(vinyl chloride) filled with ground calcium carbonate particles during a tensile test was studied. The particles were prepared by crushing natural raw crystalline limestone. For this purpose, 10–50 parts of the particles having two different mean sizes (2 and 8 μm) without further surface treatment were mixed with 100 parts of poly(vinyl chloride) and 3 parts of lead stearate as a stabilizer using a mixing roll. A tensile test was carried out using a dumbbell specimen. As a result, the yield stress decreased with increase in the particle content; however, there was no significant influence of particle size. From scanning electron microscopic observations of the specimen's surfaces during the tensile test, it was found that the particle/matrix interfaces were delaminated and formed voids around the particles when the applied stress approached the yield stress, that is, the particles acted as voids and the matrix around the voids was plastically deformed effectively. These observations appear to be the reason for the decrease of yield stress by the incorporation of the particles. © 1998 John Wiley & Sons, Inc. J. Appl. Polym. Sci. 70: 311–316, 1998     

AZ31镁合金变路径压缩过程中解孪晶行为分析

对AZ31镁合金轧制板材进行RD-ND-RD-ND(RD-rolling direction,轧向;ND-normal direction,法向)的变路径压缩实验,研究了变形过程中的力学性能,并采用EBSD技术跟踪了上述变形过程中晶粒取向变化,分析了孪晶变体的启动情况。结果表明,在变路径压缩过程中,依次对应{10 12}拉伸孪晶-{10 12}解孪晶-{10 12}拉伸孪晶-{10 12}解孪晶的微观变形机制。首次解孪晶使屈服强度下降明显,而后续的孪晶和解孪晶过程的屈服强度都增加,且两者差值很小。解孪晶过程中孪晶变体的启动遵循Schmid定律,但出现明显的选择性,解孪晶过程都由t3或t4变体完成。     

三维整体高翅片强化传热铝管刨削成形机理

为了高效加工出三维整体高翅片强化传热管,提出采用多刀刨削加工三维整体高翅片强化传热管的制造方法——利用在基管上同时刨削出多片不脱离工件的、不发生卷曲的切屑作为三维整体高翅片强化传热管的翅片。研究刀具前角、切削厚度对切屑卷曲的影响,初步探讨翅片刨削成形即切屑不卷曲的机理。结果表明,切屑不卷曲的条件是当刀具前角为60°或55°时,切削厚度在0.15~0.25 mm之间,或者前角为50°,切削厚度在0.1~0.2 mm之间时,切屑不发生卷曲;切屑不卷曲的机理在于切屑根部没有发生明显的剪切变形。     

基于锥形电极的三维型腔精确加工方法研究

提出并分析了在利用圆锥形电极定长补偿方法分层加工三维型腔实验时,其第一层第二道加工切除残余突起后形成的实际加工深度与理论分层厚度的差异,该差异存在于加工时采用的关键加工参数补偿长度的误差。进而探究并提出了精确计算第二道加工时补偿长度的方法,并通过实验验证了该补偿长度的准确性,从而使第一层两道加工后形成的加工深度达到理论值。最后,利用该方法进行两层的三维型腔加工实验,由此证明型腔加工效果良好,满足型腔尺寸及形状精度的要求。     

聚合物材料脆韧转变判据及影响因素分析

综述了聚合物共混增韧机理包括弹性体增韧、刚性粒子增韧、弹性体与刚性粒子协同增韧等研究进展；着重介绍了临界基体层厚度、损伤竞争准数、分子链参数、临界界面黏结条件、临界特征长度等几种源于单一粒子填充的脆韧转变判据，并分析其在复合粒子填充改性聚合物中的适用性。此外，还结合增韧机理和脆韧转变判据讨论了基体性能、分散相状态及相间界面黏结强度等因素对复合体系韧性的影响，提出寻找合适的复合分散相、适当调整复合粒子的结构比例、改善相间界面黏结以及设计最佳断裂路径仍将是今后努力的方向。     

板翅式换热器翅片通道中流体流动与传热的计算流体力学模拟

针对平直形和锯齿形两种不同翅片类型,利用计算流体动力学(CFD)软件FLUENT对板翅式换热器的微小通道进行了模拟,得出了通道中流体的流动与传热特性.计算结果表明,在相同情况下,平直形和锯齿形翅片中冷热流体的局部传热系数的最大值都出现在入口处;在锯齿形翅片的相邻2个锯齿的交错面上,流体的局部传热系数和压力存在突变,流体的边界层厚度要薄于在平直形翅片中的厚度,流体的局部换热系数要和压损大于其在平直形翅片中的值.     

屈服耗能隔墙的减震性能

将消能减震概念应用于非结构构件,提出一种屈服耗能隔墙。该隔墙在小震下为主体结构提供可量化的刚度支持,大震时提供可调节的耗能能力支持。通过对屈服耗能隔墙试件进行不同耗能元件数量下的静力往复试验,研究了该类型隔墙的消能机理与破坏模式,并基于IDARC程序中的柱单元对试件进行模拟,获得了消能元件数量与隔墙滞回参数之间的量化关系,提出了在IDARC程序中模拟设置屈服耗能隔墙的方法。通过对一个6层钢筋混凝土框架进行不同屈服耗能隔墙设置方案下的动力时程分析,发现屈服耗能隔墙的设置能够有效减小结构的地震反应、降低结构的损伤;框架中耗能隔墙数量的增加会使结构的层间位移显著减小,而隔墙数量相同时,隔墙中耗能元件数量的增加并不会导致结构层间位移发生明显变化。