Robust phase demodulation of interferograms with open or closed fringes

We present two robust algorithms for fringe pattern analysis with partial-field and closed fringes. The algorithm for partial-field fringe patterns is presented as a refinement method for precomputed coarse phases. Such an algorithm consists of the minimization of a regularized cost function that incorporates an outlier rejection strategy, which causes the algorithm to become robust. On the basis of the phase refinement method, we propose a propagative scheme for phase retrieval from closed-fringe interferograms. The algorithm performance is demonstrated by demodulating closed-fringe interferograms with complex spatial distribution of stationary points and gradients in the illumination components.     

微结构对泡沫材料蠕变性能的影响

针对较低密度开孔泡沫的正四面体模型,通过引入支柱结点处的体积修正使新模型能够用于预测较大密度范围内的泡沫材料的蠕变性能,并且基于该修正模型,分析了斜支柱的弯曲变形机制以及剪切变形机制对蠕变应变率的影响。结果表明:当泡沫材料的相对密度较低时,支柱的弯曲变形机制决定了其蠕变速率;而当相对密度较高时,支柱的剪切变形作用机制开始主导其蠕变速率。通过与实验结果的比较验证了本文预测的有效性。      

Viscoelastic behaviour of composite materials with conventional- or negative-Poisson's-ratio foam as one phase

This article describes experimental investigations of viscoelastic properties of composites consisting of conventional and re-entrant negative-Poisson's-ratio copper foam as a matrix, with the following high-loss-filler materials: viscoelastic elastomer, solder, and indium. The viscoelastic properties of gallium and several ferrites were also determined. The loss tangent of the copper-elastomer composite substantially exceeded the (lower) Voigt limit; the loss tangent of the copper-solder and copper-indium composites were close to the (upper) Hashin limit for the two-solid phases and one-pore phase.     

多孔泡沫金属磁流变液阻尼材料及其力学性能研究

基于多孔泡沫金属的结构性能,研制一种新型的磁流变液阻尼材料,并搭建测试系统,研究其力学性能。在该材料中,磁流变液由于毛细管力的作用储存在多孔泡沫金属里面,在磁场作用下被抽出到剪切间隙内并产生磁流变效应;利用搭建的测试系统,研究多孔泡沫金属的材料、外加电流、剪切间隙和剪切应变率等参数对多孔泡沫金属磁流变液阻尼材料力学性能的影响,结果表明,设计的多孔泡沫金属磁流变液阻尼材料可产生明显的磁流变效应,在相同情况下,采用多孔泡沫金属铜时,多孔泡沫金属磁流变液阻尼材料具有最大的剪切转矩。     

中低应变率下闭孔泡沫铝动态力学性能研究

为探索闭孔泡沫铝的动态力学性能与吸能特性,基于万能材料试验机和高速液压伺服材料试验机在常温下分别对闭孔泡沫铝在准静态和中应变率下(0.001~100s^-1)的动态力学性能进行了测试,分析了不同应变率、不同相对密度和不同泡沫铝基体特性下闭孔泡沫铝的应力应变曲线特征和吸能特性变化。研究结果表明:中低应变率下的纯铝基体泡沫铝并不具备应变率效应,高脆性、相对密度较小的泡沫铝具备更好的吸能特性,塑性和脆性基体泡沫铝变形带分别呈现“V”形和“X”形,脆性基体泡沫铝同样不具备应变率效应。     

Designing materials with prescribed elastic properties using polygonal cells

An extension of the material design problem is presented in which the base cell that characterizes the material microgeometry is polygonal. The setting is the familiar inverse homogenization problem as introduced by Sigmund. Using basic concepts in periodic planar tiling it is shown that base cells of very general geometries can be analysed within the standard topology optimization setting with little additional effort. In particular, the periodic homogenization problem defined on polygonal base cells that tile the plane can be replaced and analysed more efficiently by an equivalent problem that uses simple parallelograms as base cells. Different material layouts can be obtained by varying just two parameters that affect the geometry of the parallelogram, namely, the ratio of the lengths of the sides and the internal angle. This is an efficient way to organize the search of the design space for all possible single‐scale material arrangements and could result in solutions that may be unreachable using a square or rectangular base cell. Examples illustrate the results. Copyright © 2003 John Wiley & Sons, Ltd.     

消失模EPS模型材料表征及性能的研究

为了探究消失模EPS模型的表面粗糙度影响因素、应力应变特征以及消失模EPS模型材料的热解规律和内部胞腔结构形态,达到降低消失模铸件的表面粗糙度,科学制定消失模工艺过程的控制参数,选择适合消失模工艺的合金材料,控制铸件内碳化物残留量,提高消失模铸件的表面质量和力学性能.本文采用激光粒度分析仪对用于消失模EPS产品模型成形...     

磁流变液导电性能研究

磁流变液的安全性是其应用推广的重要保障,对磁流变液导电特性（绝缘特性）的研究有着重要意义。实验的目的是测量出磁流变液的阻值随磁场变化规律,并分析其导电性能。设计制作了磁流变液电阻,该电阻是上下底面为金属的圆柱体容器,容器内装满磁流变液。在外加磁场作用下,由于两金属极板间的磁流变液的磁性颗粒连接成链,使极板间的导电性能发生变化,从而导致电阻减小。推导出了电阻表达式,表明与实验结果相符。     

Fracture and microstructure of open cell aluminum foam

SEM and EDS measurements were used to scrutinize the microstructure of Duocel open cell 6101 aluminum foam in relation to its fracture properties. In-situ SEM tensile tests on the open cell aluminum foam were performed to investigate the different fracture modes of struts and Aramis/Digital Image Correlation software was used to map the strain in individual struts. Observations during tensile tests showed that the microstructure of the struts has a great influence on the fracture behaviour of the foam. In particular AlFeSi-precipitates, which are due to the casting of the 6101 aluminum alloy, and the morphology of the foam alters the fracture mode of the struts in the foam from transgranular to intergranular. Less energy is needed for intergranular fracture of struts and the strain to failure of the foam is decreased due to weak individual struts.     

再生聚乙烯回掺量对无卤阻燃保温泡沫材料性能的影响

将再生聚乙烯(RPE)与低密度聚乙烯(LDPE)共混改性,采用红磷和无卤阻燃PE母粒,利用二段发泡工艺进行发泡,制备无卤阻燃保温材料。研究了RPE回掺量对材料力学性能、阻燃性能、保温性能的影响,并进行了燃烧烟气成分分析。结果表明,掺入RPE,不仅可以降低成本,而且可以改善纯LDPE凝胶率低的问题,更容易采用二段发泡法,各项性能均有所改善。当RPE回掺量为50%时性能指标达到最佳:发泡倍率为32(体积倍率),氧指数为30,垂直燃烧速度13mm/min,吸水率为0.0016g/cm3,导热系数为0.017W/(m.K)。材料燃烧后,烟气主要成分为聚乙烯热裂解产物,表明聚乙烯泡沫材料在燃烧过程中与氧气的接触不好,未检测到二噁英等有毒气体。     

Cushioning properties of convoluted foam

Convoluted polyurethane foam was tested for its cushioning ability in controlled drop tests using a cushion tester. The purpose of the tests was to relate the peak acceleration transmitted to the falling weight to key geometric features of the cushion, such as base thickness and area, along with finger height and spacing. It was found that the fingers had the effect of reducing the impact velocity in a predictable manner, allowing the convoluted cushion to be treated as a block design so that published cushion curves for the same material could be used to obtain the peak acceleration. In effect, convoluted foam behaves like a block cushion of the size of its own base in a drop from a reduced height, the reduction being several times the finger height. Copyright © 1999 John Wiley & Sons, Ltd.     

开孔金属泡沫有效热导率的理论分析与实验研究

采用能量守恒定律和光学厚近似法,建立了开孔金属泡沫有效热导率的计算模型,分析了温度和压力等因素对传热的影响,并应用高温真空石墨加热炉对开孔金属泡沫的有效热导率进行了实验测量.理论值与测量值基本吻合,各个测量点的平均相对误差<5%,最大相对误差低于10%.结果表明,开孔泡沫金属的有效热导率随温度和压力的增加而增大,在低温情况下(T<100℃),开孔泡沫金属内部的传热机制主要为固体导热;在高温情况下(T>400℃),辐射成为开孔泡沫金属的主导传热机制;在低压下,气体导热可以忽略不计,但随着压力的增大,气体导热加大对传热的影响.     

泡沫碳化硅陶瓷的导电性能

采用高分子热解和反应烧结方法制备出泡沫碳化硅陶瓷，研究了泡沫碳化硅陶瓷的体积分数变化和钛的掺杂对泡沫碳化硅陶瓷骨架导电性能的影响．结果表明：随着泡沫碳化硅陶瓷的体积分数提高，泡沫碳化硅陶瓷的电阻率降低，这是泡沫碳化硅陶瓷筋中部碳化硅的面积增加所引起的；掺杂的钛转变成TiSi2导电相改善了泡沫碳化硅陶瓷的导电性能．TiSi2呈现离散和团聚两种形态分布，以不规则的形状位于碳化硅晶界之间，在碳化硅中作为施主杂质．泡沫碳化硅陶瓷表现出的正或负温度系数取决与掺杂的钛量的多少．     

The equivalence of two-station closed and open serial production systems with finite buffers

This note presents a simple method for transforming any two-station closed serial production system with finite buffers into an equivalent two-station open system by the appropriate removal of job carriers or buffers.     

The equivalence of two-station closed and open serial production systems with finite buffers

This note presents a simple method for transforming any two-station closed serial production system with finite buffers into an equivalent two-station open system by the appropriate removal of job carriers or buffers.     

Buckling and collapse of open and closed cylindrical shells

The buckling of a finite section of a cylindrical shell resembling a two-dimensional contact lens, and the collapse of a tubular shell of infinite extent are considered. The deformation is due, respectively, to the application of an edge force or to a negative transmural pressure. In both cases, the shell develops elastic bending moments due to the deformation from a specified resting shape according to a linear constitutive equation, accompanied by in-plane and transverse shear tensions. In the case of a section of a shell with a flat resting shape, classical results due to Euler and Love show that, as the applied edge force is increased beyond a sequence of thresholds, an infinite family of deformed shapes becomes possible corresponding to buckled states that bifurcate from the zero-curvature resting configuration. It is shown here that a corresponding infinite family of shapes is also possible for a finite shell whose resting shape is a section of circle. These shapes, however, no longer arise from bifurcations, but rather constitute disconnected solution branches of a nonlinear boundary-value problem. A closed cylindrical shell whose cross-section has a circular resting shape exhibits similar bifurcations when the difference between the exterior and interior pressure exceeds a sequence of thresholds, but a shell with a non-circular resting shape deforms into a multitude of shapes described by isolated solution branches. The computed two-dimensional buckled shapes are used to reconstruct the three-dimensional shape of a slowly collapsing fluid-conveying vessel. The reconstruction procedure involves stacking together cross-sections at axial positions that are found by integrating the differential equation determining the axial pressure distribution in unidirectional pressure-driven flow, subject to a constant flow rate. The dimensionless coefficient relating the local pressure gradient to the flow rate is computed by solving the Poisson equation governing unidirectional viscous flow using a boundary-element method, and expressing the flow rate as a boundary integral involving the shear stress which is available from the solution of the boundary-integral equation. In an appendix, the energy of the bending state is discussed with reference to specific choices made by previous authors in various branches of science and engineering.     

Shear properties of CMB syntactic foam

In this research, a triaxial shear test is used as a means to provide yield surface data as well as other strength characteristics for carbon microballoon (CMB) syntactic foam. Additionally, pure shear tests and tensile tests are used to probe areas of this stress space not included in the triaxial shear tests. The data are used to characterize the material’s yield strength in stress space. The determined yield surface, the strain and other deformational behavior characteristics provide the necessary information for an accurate model and engineering design. The CMB foam specimens were divided into two sets: one with Thornel pitch-based carbon fibers and one without; both use Kerimid 601 as the binder. The CMB syntactic foam with fibers exhibited lower shear strength than the CMB syntactic foam without fibers. This is evident not only in the determined shear envelopes but also in the values obtained for the hydrostatic yield of both foams. Complementary analysis of the blending process of mixing fibers with CMB has been shown to destroy the microballoons and thus reduce the foams strength. The consequences of incorporating alternative materials can be verified with further testing.     

Tension,compression and shear fatigue of a closed cell polymer foam

A closed cell foam of polymetacrylimide (Rohacell) with three different densities is studied. The foam is tested quasistatically in tension, compression and shear. The tensile properties scale very well with the relative density of the foam, but the compression and shear properties do not scale the same way. It is believed to be due to cell edge and cell wall buckling being the dominated deformation mechanism in compression and shear for lower densities that does not occur for higher densities. Fatigue testing is then performed in tension, compression and shear. It is seen that for all load cases and densities, the fatigue life can be plotted using Basquin’s law. The results also show that the different failure mechanisms found in the static tests are the same in fatigue. This means that the fatigue life for different load types exhibit different failure mechanisms. This shows not only as a clear difference in the stress levels for fatigue failure, but also on the slope in the fatigue life relation.