高分子基功能复合材料的熔融沉积成型研究进展

3D打印又称增材制造技术,是基于材料、机械控制、计算机软件等多学科交叉的先进制造技术,可得到传统加工不能制备的形状复杂制件.熔融沉积成型(FDM)是目前最通用的3D打印技术之一,具有设备简单、成本低、操作便捷等特点,广泛应用于航空航天、医疗、汽车工业等领域.本文介绍了国内外3D打印技术的整体布局、发展和规划,总结了常见...     

熔融沉积打印微纳米生物质填料增强聚乳酸基复合材料的研究进展

熔融沉积成型(Fused deposition modeling,FDM)因其制造成本低廉和工艺简易等特点成为现今增材制造(Additive manufacturing,AM)技术中应用最广泛的一种类型,而聚乳酸(Polylactic acid,PLA)也因其良好的可生物降解性和生物相容性成为FDM线材的主要原料。但是,PLA较差的脆性、韧性及热稳定性等缺点严重限制了其打印产品在市场上的应用。因此,在PLA线材中加入某种或多种填料是解决其自身缺点的重要措施。其中,生物质填料是一种比较理想的选择,在PLA中加入生物质填料不仅可以有效克服基材的性能缺陷,而且产品具有良好的可生物降解性和环境友好性。本文综述了近几年来FDM打印生物质填料增强PLA复合材料的研究进展,阐释不同尺度结构(由微米尺寸到纳米尺寸)的生物质增强填料(如木粉、天然纤维、纳米纤维素)对PLA基复合材料的性能影响,并分析和总结复合材料的性能改善原因及其界面相容机制,最后对FDM打印PLA基复合材料的未来发展进行了展望。     

Recent progress of 3D printed continuous fiber reinforced polymer composites based on fused deposition modeling: a review

Journal of Materials Science - 3D Printing, utilizing a layer-by-layer deposition of materials, is advantageous to manufacture parts as it involves fewer process steps, provides great flexibility...     

Osteogenic differentiation of mesenchymal progenitor cells in computer designed fibrin-polymer-ceramic scaffolds manufactured by fused deposition modeling

Biomimetic scaffolds offer great potentials in the development of bone analogs for tissue engineering. The studies presented in this paper focus specifically on the osteogenic potential of the novel PCL/CaP matrices and its degradation behavior. Biodegradable Polymer-ceramic Scaffolds were fabricated using the solid free form fabrication technology: Fused Deposition Modeling (FDM). The scaffold architecture was characterized by a honeycomb-like design and a complete interconnectivity of the pores. Human mesenchymal stem cells (MSCs) were seeded together with fibrin glue into PCL/CaP scaffolds and cultured in vitro for periods of up to eight weeks. Cellular adhesion, proliferation and osteogenic differentiation were assessed in these constructs using a range of histological and microscopic techniques. In additional experiments, degradation was assessed by measuring mass loss, diameter change, molecular weight change and by scanning electron micrographs. MSCs were able to adhere, migrate, and differentiate along the osteogenic lineage with in these scaffolds. The PCL/CaP scaffolds showed up to 27 fold increased degradation of compared to PCL scaffolds.     

Plasma-assisted deposition of metal fluoride coatings and modeling the extinction coefficient of as-deposited single layers

We realized metal fluoride coatings with a high packing density and a low extinction coefficient by plasma (ion)-assisted deposition. The densification can be performed by different types of plasma sources, e.g., by a Leybold LION source and a Leybold APSpro, respectively. But the as-deposited coatings show a characteristic absorption behavior, whereas the absorption losses can be reduced in a postdeposition UV treatment step. We show experimental results of the plasma-assisted metal fluorides before and after the UV treatment and present a new model that allows us to describe and calculate the characteristic absorption losses of LaF3, MgF2, and AlF3.     

A moving Griffith crack at the interface of two dissimilar elastic layers

The anti-plane shear problem of a Griffith crack traveling with a constant velocity at the interface of two dissimilar isotropic elastic layers is considered. Integral transform method is used to reduce the problem to the solution of a singular integral equation which is further reduced, by using Chebyshev polynomials, to a system of algebraic equations. The results for the particular cases of a moving Griffith crack at the interface of a layer and a half-space and two half-spaces are derived. Numerical results for the stress intensity factor are displayed graphically.     

Hysteresis in the phase-slip state of superconducting filaments

Recently some papers on measurements of the I-V characteristics (where V is the time-averaged voltage) of superconducting indium microbridges ¹ as well as tin and zinc whiskers ^2,3 driven by a dc current into the phase-slip state have appeared. Special emphasis was placed on a discussion of the hysteresis, which is well-known in such experiments (see, e.g., Refs.1–18 in Kramer and Rangel ⁴ ). The hysteresis was compared with the predictions of the generalized time-dependent Ginzburg-Landau (GTDGL) equations for dirty superconductors in local equilibrium. ^4,5 Unfortunately these predictions represent the only results in this context derived ultimately in a rigorous fashion from the standard microscopic theory of superconductivity. Comparison was also made with a model by Kadin, Smith, and Skocpol (KSS), ^6,7 which gives a much smaller hysteresis. The authors of Ref. 1 found good agreement with the KSS model. The authors of Refs. 2 and 3 found a hysteresis which is larger than that of the KSS model, but still considerably smaller than predicted by GTDGL theory. They proposed a generalization of KSS which can be fitted to the data.     

Determination of the state density at the Si-SiO2 interface

The problem of determining the density of surface states at the Si-SiO₂ interface from the quasi-static capacitance of a MOS capacitor is reconsidered in full detail. The errors introduced by the usual zero kelvin approximation are evaluated, an improved semiclassical approximation is proposed and its limits are estimated, an exact formula is found, and a numerical method is developed.The discussion of this formula reveals the existence of fundamental difficulties which are concealed by the approximate methods. These difficulties are common to several problems in solid state physics.     

Formation of boride layers at the Fe–25% Cr alloy–boron interface

Two boride layers based on the FeB and Fe₂B compounds are formed at the interface between a Fe–25% Cr alloy and boron at 850–950 °C and reaction times up to 12 h. The characteristic feature of both layers is a pronounced texture. Each of two boride layers is compositionally two-phase. The outer layer consists of the (Fe,Cr)B and (Cr,Fe)B phases. The inner layer comprises the (Fe,Cr)₂B and (Cr,Fe)₂B phases. The diffusional layer-growth kinetics are close to parabolic and can alternatively be described by a system of two non-linear differential equations, also producing a fairly good fit to the experimental data. Annealing of a borided Fe–Cr sample in the absence of boriding media results in the disappearance of the (Fe,Cr)B–(Cr,Fe)B layer, with the (Fe,Cr)B phase disappearing first. Microhardness values are 21.0 GPa for the outer layer, 18.0 GPa for the inner layer and 1.35 GPa for the alloy base. The abrasive wear resistance of the (Fe,Cr)B–(Cr,Fe)B layer, found from mass loss measurements, is more than 150 times greater than that of the alloy base.