挤出型3D打印混凝土力学性能研究进展

介绍了3D打印混凝土的特点与前景,综述了挤出型工艺的3D打印混凝土的压、拉、折、剪基本力学性能以及增强措施.研究表明:打印层在喷嘴的挤压作用下密实度有所提高,但同时层间易形成薄弱界面,造成性能的各向异性,通过调整胶凝材料、掺入纤维、优化工艺、水浴养护、布筋等措施能有效改善.此外,提出了还需进一步研究的问题.     

Effect of anisotropic yield functions on the accuracy of hole expansion simulations

The deformation behavior of 780 MPa grade dual-phase steel sheet subjected to hole expansion is investigated both experimentally and analytically to clarify the effect of the material model (anisotropic yield function) on the predictive accuracy of finite element analysis of hole expansion. Biaxial tensile tests of the material were conducted; contours of plastic work and the directions of plastic strain rates are precisely measured and are in good agreement with those predicted from the Yld2000-2d yield function with an exponent of 4 ( [Barlat et al., 2003] and [Yoon et al., 2004]). Finite element and experimental analyses on the hole expansion of the material were conducted. The Yld2000-2d yield function with an exponent of 4 provides closer agreement with the experimental results than other yield functions. Consequently, the anisotropic yield functions significantly affect the predictive accuracy of the deformation behavior of the steel sheet subjected to hole expansion, and the biaxial tensile test is effective for identification of the appropriate anisotropic yield function to be used for hole expansion simulation.     

Finite element dynamic stability analysis of laminated composite skew plates containing cutouts based on HSDT

The finite element dynamic stability analysis of laminated composite skew structures subjected to in-plane pulsating forces is carried out based on the higher-order shear deformation theory (HSDT). The two boundaries of the instability regions are determined using the method proposed by Bolotin. The numerical results obtained for square and skew plates with or without central cutout are in good agreement with those reported by other investigators. The new results for laminated skew plate structures containing cutout in this study mainly show the effect of the interactions between the skew angle and other various parameters, for example, cutout size, the fiber angle of layer and thickness-to-length ratio. The effect of the magnitude of the periodic in-plane load on the dynamic instability index is also investigated.     

Hierarchical reinforcement of polyurethane-based composites with inorganic micro- and nanoplatelets

Hierarchically reinforced structures are widespread in nature but less common among man-made materials. In this paper, we show that polyurethane-based thermoplastic polymers can be hierarchically reinforced with laponite nanoplatelets and alumina microplatelets to reach strength and elastic modulus that are, respectively, 7- and 29-fold higher than that of the pure polymer matrix (91.7 MPa and 6.97 GPa, respectively). We find that the selective reinforcement of the polyurethane hard domains with laponite nanoplatelets is key to keep the polymer matrix sufficiently ductile for the incorporation of high concentrations of alumina microplatelets. Effective reinforcement of the polymer with microplatelets of different surface chemistries was only possible after annealing the composite at 130 °C to promote strong bonding at the oxide/polymer interface. Large-area composite films and bulk parts exhibiting good alignment of alumina microplatelets were obtained through conventional tape-casting. The concept of hierarchical reinforcement demonstrated here can be explored to obtain composite materials covering a wide range of mechanical properties using only a few reinforcing building blocks within the same polymer matrix.     

Damage characterization and modeling of a 7075-T651 aluminum plate

In this paper, the damage-induced anisotropy arising from material microstructure heterogeneities at two different length scales was characterized and modeled for a wrought aluminum alloy. Experiments were performed on a 7075-T651 aluminum alloy plate using sub-standard tensile specimens in three different orientations with respect to the rolling direction. Scanning electron microscopy was employed to characterize the stereology of the final damage state in terms of cracked and or debonded particles. A physically motivated internal state variable continuum model was used to predict fracture by incorporating material microstructural features. The continuum model showed good comparisons to the experimental data by capturing the damage-induced anisotropic material response. Estimations of the mechanical stress–strain response, material damage histories, and final failure were numerically calculated and experimentally validated thus demonstrating that the final failure state was strongly dependent on the constituent particle morphology.     

相场模型模拟强界面能各向异性作用下晶体生长

用Eggleston等提出的方案对界面能各向异性函数进行重整化处理,并使用相场模型对强各向异性情形下的晶体生长进行了模拟.在晶体平衡形态模拟中再现了晶向缺失现象,并与理论预测结果相一致.在自由枝晶生长过程中,当各向异性低于临界值时.枝晶生长速度随着各向异性系数增大而增大;在临界值附近生长速度突然降低5%;当高于临界值时生长速度又开始增加直到在0.20处达到最大值,其后基本不变.     

Synthesis and optical properties of azobenzene side chain polymers derived from the bifunctional fumaric acid and itaconic acid

Three type polymers containing the same azobenzene side chain group with different backbone structures, poly(DMAz6Fm), poly(DMAz6It) and poly(MAz6Ac) derived respectively from fumaric acid, itaconic acid and acrylic acid, were synthesized. The dependence of photo-response properties on the polymeric architecture was investigated for the solutions and films. By irradiation of the linearly polarized light (436 nm), uniaxial orientations of the thin films were induced and anisotropic properties were investigated by measurements of the order parameters and birefringence values.     

IN-PLANE MOISTURE TRANSPORT IN PAPER DETECTED BY MAGNETIC RESONANCE IMAGING

Magnetic resonance imaging was used to visualize in-plane moisture transport in laboratory-made handsheets, heavy paperboard, and polyethylene-coated paperboard. Beginning with wet samples sealed on both surfaces, the moisture content was reduced through evaporation from the outside edges. The diffusion of moisture to the outside edges, i.e., in the plane of the sheets, was found to be isotropic with respect to the sample machine and cross directions. Isotropic in-plane moisture diffusion was observed for samples exhibiting a relatively high degree of fiber orientation, and under conditions of forced convection with air flow rates up to 10 L/min past the outside edges.     

Study the Influence of the Bank Energy on the Dynamical Pinch in Plasma Focus

The plasma focus discharge can generate, accelerate and pinch the plasma up to high density and temperature in a pulsed mode manner. Applications aspects of discharge require high efficiency of the fusion products. This situation acquires optimized operational parameters for the proper discharge. In this article, we have studied the plasma parameters and neutron performance dependency on bank energy. First, analytical expressions are derived from the equation of motion for the plasma particles in the radial phase. Then, the related fusion neutrons, both thermal and non-thermal, together with the discharge anisotropy in the low pressure regimes for the ‘Dena’ plasma focus device as function of bank energy are presented. The analytic models are compared with experimental data.