Mechanical behavior of carbon fiber composite lattice core sandwich panels fabricated by laser cutting

This paper presents a novel method for rapid fabrication and prototyping of low-density carbon fiber sandwich panel cores based on laser beam cutting (LBC). Using LCB, sandwich panels with lattice core constructions with oblique and vertical strut morphologies were fabricated from two fiber-orientation architectures. Scanning electron microscopy images illustrate the relatively small extent of damage from laser cutting. The shear strength of the lattice cores was improved by eliminating core-to-face sheet bond failures. Crushing and shear responses of fabricated truss cores were measured, and analytical models are presented to predict the stiffness, strength and dominant failure modes under each loading condition. The sandwich-panel cores investigated appear to be promising candidates for lightweight systems and multifunctional applications.     

Indentation of Foam-Based Polymer Composite Sandwich Beams and Panels Under Static Loading

Foam core composite sandwich structures are highly susceptible to damage when subjected to localized loading. Therefore, thorough study of the role of factors such as face sheet thickness, indentor diameter value, and crosshead displacement rate in indentation events is important. The objective of the present work is to investigate experimentally and numerically the influence of these factors on the nonlinear static indentation behavior of sandwich beams and panels consisting of glass fiber/resin face sheets and PVC (polyvinylchloride) foam core. Static indentation tests are carried out on sandwich composite beam and panel specimens using steel cylindrical and spherical indentors, respectively. Numerical models are developed for simulating the mechanical response of sandwich structures subjected to localized indentation beyond the limit of elastic deformation in the foam core. In this relation, the *CRUSHABLE FOAM and the *CRUSHABLE FOAM HARDENING options in the ABAQUS finite element program system are used. The numerical analysis results demonstrate good agreement with experimental data. It is found that increasing the face sheet thickness and indentor diameter value leads to increase in the load (for a given displacement). It is shown also that the indentation behavior does not exhibit sensitivity to crosshead displacement rate over the conditions considered in the present work.     

Inertial stabilization of buckling at high rates of loading and low test temperatures: Implications for dynamic crush resistance of aluminum-alloy-based sandwich plates with lattice core

In the present study, the dynamic compressive behavior of aluminum-alloy-based tetrahedral-core truss structures is investigated as a function of impact velocity using a split Hopkinson pressure bar. The results are used to understand the phenomenon of buckling in truss structures as a function of loading rates and test temperatures, and its implication on the dynamic crush resistance of tetrahedral-truss-based sandwich structures. In order to understand the effects of the flow strength of the core on the dynamic crush resistance, truss structures of both T6 and OA heat-treatments of AA6061 were investigated. A high-speed digital camera was used to record the sequence of the deformation and failure events that occur during the dynamic compression and failure of the truss sub-elements. A buckling instability was observed to occur consistently for both the T6 and OA microstructures at all test temperatures employed in the present study. Moreover, the T6 heat-treatment and the lower-than-room test temperatures significantly increase the specific energy absorption capabilities of the truss structures.     

Structural performance of metallic sandwich beams with hollow truss cores

The article focuses on the structural performance of sandwich beams with hollow truss lattice cores made from a ductile stainless steel. The trusses are arranged in an orthogonal (cross-ply) configuration, in either ±45° (diamond) or 0°/90° (square) orientations with respect to the face sheets. The responses in shear, tension and compression, as well as simply supported and fully clamped bending, are measured for specimens with both core orientations. While the two cores perform equally well in compression, the diamond orientation exhibits higher shear strength but lower stretch resistance. For bend-dominated loadings of the sandwich beams, the core in the diamond orientation is preferred because of its higher shear strength. For stretch-dominated loadings encountered in large-displacement, fully clamped bending, the square orientation is superior. Models of core and beam yielding are used to rationalize these observations. Optimizations are then performed to identify strong lightweight designs and to enable performance comparisons with other sandwich structures.     

Orthogonal cutting mechanics of multi-directional carbon fiber reinforced polymer with interlaminar bonding effect

This paper determines the chip formation mechanism, fiber-matrix failure modes, and cutting forces in orthogonal cutting of multi-directional carbon fiber reinforced polymer (MD CFRP) with interlaminar bonding effect. The cutting experiments show that the varying chip formation angles with different fiber orientations in cutting unidirectional plies converge for MD CFRP. A new analytical mechanics model for cutting MD CFRP is developed to predict the chip formation angle and failure modes based on the minimum energy principle for all plies. The model with experimental validation reveals the different cutting mechanisms between UD and MD CFRPs.     

Moisture ingression in honeycomb core sandwich panels

Moisture ingression was studied in several composite sandwich panels, in which hydration was applied over a large surface area at the panel edges. Significant moisture ingression occurred in panels with cores of Korex (based on a substrate of a fiber pulp paper) and HRP (consisting of a woven-glass-fiber substrate with a polymer coating) of different density. Ingression was more rapid than in panels with hydration applied locally. Ingression followed an exponential pattern in time in most cases, in harmony with diffusion theory.     

Design and fabrication of formable CFRTP core sandwich sheets

Sandwich structures have had remarkable success in engineering applications, but their applications are mostly limited to flat panel types because of their poor formability. To expand the range of applications of sandwich structures, new formable CFRTP (carbon fibre reinforced thermoplastic) core sandwich sheets are proposed, where a truncated dome core structure is designed to increase formability and structural performance. This paper first introduces the design methods followed by the fabrication processes and finally reports the flexural properties and formability of the proposed core sandwich sheets. Fabricated sandwich sheets were successfully subjected to hat bending without failure.     

Flexural Properties of E Glass and TR50S Carbon Fiber Reinforced Epoxy Hybrid Composites

A study on the flexural properties of E glass and TR50S carbon fiber reinforced hybrid composites is presented in this paper. Specimens were made by the hand lay-up process in an intra-ply configuration with varying degrees of glass fibers added to the surface of a carbon laminate. These specimens were then tested in the three-point bend configuration in accordance with ASTM D790-07 at three span-to-depth ratios: 16, 32, and 64. The failure modes were examined under an optical microscope. The flexural behavior was also simulated by finite element analysis, and the flexural modulus, flexural strength, and strain to failure were calculated. It is shown that although span-to-depth ratio shows an influence on the stress-strain relationship, it has no effect on the failure mode. The majority of specimens failed by either in-plane or out-of-plane local buckling followed by kinking and splitting at the compressive GFRP side and matrix cracking combined with fiber breakage at the CFRP tensile face. It is shown that positive hybrid effects exist for the flexural strengths of most of the hybrid configurations. The hybrid effect is noted to be more obvious when the hybrid ratio is small, which may be attributed to the relative position of the GFRP layer(s) with respect to the neutral plane. In contrast to this, flexural modulus seems to obey the rule of mixtures equation.     

钢面板泡沫铝夹心板的三点弯曲行为

采用胶粘法制备大尺寸钢质泡沫铝夹心板,测试夹心板的三点弯曲强度,分析面板厚度、芯层厚度对夹心板弯曲性能的影响规律,研究弯曲载荷作用下的夹心板失效机理。结果表明：钢质泡沫铝夹心板可承受很高的弯曲载荷,夹心板抗弯强度随着芯层泡沫铝厚度的提高而提高。增加钢面板的厚度,夹心板抗弯强度整体呈增强趋势。当面板厚度为8 mm、芯层厚度为50 mm时,夹心板的极限抗弯强度可达66.06 kN。芯层泡沫铝内泡壁表面的大尺寸裂纹是夹心板在弯曲载荷作用下失效的主要原因;采用熔体发泡法制备的泡沫铝板材,因冷却强度过大而导致的附加应力使泡壁的强度下降,也是影响夹心板力学性能的主要因素。     

On the gas pressure forming of aluminium foam sandwich panels: Experiments and numerical simulations

Forming of light-weight highly stiff aluminium foam sandwich (AFS) panels into complex 3D components would mark a development in the manufacturing of these materials. In this work, gas pressure forming of AFS panels is investigated experimentally and using numerical simulations. Deformation behaviour of AFS panels is studied during high-temperature uniaxial tension and compression, and constitutive models are developed and incorporated into FE simulations of the gas pressure forming process. Simulation results and experimental observations show reasonable agreement and demonstrate the possibility of forming AFS panels to significant deformations while maintaining considerable core porosity.     

Mechanical properties of aluminum/polypropylene/aluminum sandwich sheets

The aluminum/polypropylene/aluminum (A1/PP/A1) sandwich sheets have been developed for potential application of these materials for automotive body panels in future high performance automobiles with significant weight reduction. The tensile properties of the A1/PP/A1 sandwich sheets were examined in the present study as well as those of the aluminum skin and the polypropylene core at room and elevated temperatures. It was found that the sandwich sheet with hard skin and low volume fraction of the polypropylene core showed the highest tensile strength, whereas that with soft skin and high volume fraction of the polypropylene core showed the lowest strength. The sandwich sheet with hard skin showed much smaller work hardening rate than that with soft skin. All sandwich sheets showed serration phenomena on their flow curves. However, the magnitude of serration was significantly diminished in the sandwich sheet with high volume fraction of polypropylene core. The tensile strength of the sandwich sheet was compared with that calculated from the rule of mixture based on the tensile strengths of the aluminum skin and the polypropylene core. The results showed that there were good agreements between the experimentally obtained values and the calculated values. From the tensile tests at elevated temperatures, it was found that the tensile strength of the sandwich sheet with high volume fraction of polypropylene core was more sensitive to temperature than that with low volume fraction of polypropylene core. During tensile deformation of the sandwich sheet, it was found that fracture first took place in the aluminum skin and then in the polypropylene core and at the interface. The interface strength was found to be strong enough to avoid premature debonding at the interface before fracture took place in the entire sandwich sheet.     

Detection of water ingress in composite sandwich structures: a magnetic resonance approach

Water ingress inside honeycomb sandwich panels during service has been linked to in-flight failure in some aircraft. There is an ongoing effort to develop nondestructive testing methods to detect the presence of water within the panels. Magnetic resonance (MR) represents an attractive approach in that it is sensitive to moisture. Using a unilateral MR sensor, testing can be applied directly to the surface of the panel. The viability of MR is demonstrated through laboratory imaging of both water within sandwich panels, as well as the adhesive itself. The detection of water using a one-sided handheld MR sensor is presented. It is shown that simple detection, as well as spatial localization of water within sandwich panels is possible.     

G20CrNi2MoA钢的回火特性及在柴油机针阀体上的应用

研究了由G20CrNi2MoA渗碳轴承钢制作的柴油机渗碳针阀体的回火特性。对该材料的化学成分、力学性能及显微组织进行了详细的检测,并研究制定了最佳的热处理工艺。在180~250 ℃不同温度下对针阀体试样进行回火处理,通过光学显微镜对针阀体座面及心部组织进行了分析,XRD检测了端面残奥含量,并用显微维氏硬度计对座面渗层及心部进行了硬度分析。结果表明,当回火温度为230 ℃时,G20CrNi2MoA钢针阀体的座面硬度可达740 HV(61.8 HRC),端面残奥体积分数为0.25%,能保证针阀体在230 ℃左右温度下具有良好的耐磨性和组织、尺寸的稳定性。试制出的针阀体寿命较长,能满足柴油机对针阀体的使用要求。     

Impact damage behavior of sandwich composite with aluminum foam core

Impact property of the sandwich composite with aluminum foam core was investigated by experiment and simulation analysis. Impact energies of 50, 70 and 100 J were applied to the specimens in impact tests. The results show that the striker penetrates the upper face sheet, causing the core to be damaged at 50 J test but the lower face sheet remains intact with no damage. At 70 J test, the striker penetrates the upper face sheet and the core, and causes the lower face sheet to be damaged. Finally at 100 J test, the striker penetrates both the upper face sheet and the core, and even the lower face sheet. The experimental and simulation results agree with each other. By the confirmation with the experimental results, all these simulation results can be applied on structure study of real sandwich composite with aluminum foam core effectively.     

金属夹芯复合板及其制备技术的发展

简要介绍了各种金属夹芯复合板的结构形式、特点及其应用领域。阐述了金属夹芯复合板按照芯材的分类以及不同种类芯材的制备方法．结合芯材的制备技术重点介绍了蜂窝芯材的制备。在金属板面与芯材的各种连接技术中介绍了胶接、钎焊连接、缝焊、激光焊以及界面瞬间液相扩散轧制等连接方法。     

泡沫铝填充波纹夹芯板面外压缩的三维效应

研究了闭孔泡沫铝板、3种空心波纹铝板和3种用环氧树脂粘接而成的闭孔泡沫铝填充波纹铝板的平面外压缩性能.泡沫填充波纹铝板不仅能显著提高抗压强度和吸能能力,而且力学性能更加稳定.泡沫填充波纹板具有明显的三维压缩效果.铝合金板材强度越小,三维延伸变形越明显.由3种不同强度的铝合金板制成的泡沫铝填充波纹板具有相似的力学性能.成...     

Development on Preparation Technology of Aluminum Foam Sandwich Panels

泡沫铝夹层板是一种综合性能优异的新型功能材料,由具有高孔隙率特性的泡沫铝芯和金属面板组成。由于该材料不仅具有泡沫铝材料所拥有的极低密度,耗能能力好,比强度和比刚度高,隔热隔音性能优越和高阻尼等优异特性,还一定程度上弥补了泡沫铝材料强度低的缺点,致使泡沫铝夹层板材料在诸如要求具有高机械强度和良好散能能力的轻型结构应用等诸多领域受到广泛关注。目前,泡沫铝夹层板材料已经引起广大研究者的高度重视。本文综合论述了泡沫铝夹层板制备技术的研究进展,并对各种制备工艺的优缺点进行了分析。     

Research on Transient Liquid Phase Diffusion Bonding of Steel Sandwich Panels Under Small Plastic Deformation

Plastic deformation was newly introduced in transient liquid phase (TLP) diffusion bonding of steel sandwich panels. The effect of plastic deformation on bonding strength was investigated through lab experiments. It was assumed that three factors, including newly generated metal surface area, deformation heat, and lattice distortion, contribute to the acceleration of interface atoms diffusion and increase of diffusion coefficients. A numerical model of isothermal solidification time was developed for TLP bonding process under plastic deformation and applied to carbon steel sandwich panels bonding with copper interlayer. A reasonable isothermal solidification time was obtained when an effective diffusion coefficient was used. Based on lab experiments, the effects of plastic deformation on interlayer film thickness and isothermal solidification time were studied through theoretical calculation with the new model. The evolution of interlayer film thickness indicates a good agreement between the calculation and experimental measurement. The results show that the isothermal solidification time is obviously reduced due to the effect of plastic deformation. Furthermore, a new steel sandwich cooling panel for heat exchanger was fabricated by TLP diffusion bonding under 13.1% plastic deformation. The test results suggest that a steel sandwich panel of inequidistant fin structure can provide enhanced heat transfer efficiency.     

Wire-woven bulk Kagome truss cores

A new type of periodic cellular metal called wire-woven bulk Kagome (WBK) is devised. For fabricating the WBK truss core, continuous helical wires are systematically assembled in six different directions. Through this method, the unit WBK structure, which guarantees high specific strength, is uniformly formed in the core. Therefore, with this fabrication process, which allows continuous assemblies, robust truss cores can be mass produced. Metal wires are selected for the WBK core because they can be easily hardened by heat treatments and simply handled for fabrication. For characterizing the deformation behavior of the WBK core under compression, the compressive properties, such as the effective elastic modulus and the peak stress, are predicted using force equilibrium and elastic energy conservation of the core, and obtained through experimental measurements using WBK specimens of different sizes. Moreover, the compressive performance of the WBK core is compared with those of well-known cores of different types, and the failure mechanisms are elucidated by finite element analysis about the compressive behavior of the core.     

Analysis of core shear stress in welded deformable sandwich plates to prevent de-bonding failure during U-bending

In this work, a multi-point resistance welding process was employed as a bonding mechanism for deformable sandwich plates with sheared dimple cores to improve productivity. During U-bending, a de-bonding failure occurred due to the shear deformation of the core. An analytic study that investigated the bending mechanism was carried out to determine the control parameter of core shear stress. The analytic estimation revealed that the shear stress of the core could be reduced drastically by increasing the clearance. In addition, from the analysis of the de-bonding failure, the de-bonding behavior with respect to clearance could be effectively predicted. The fabricated sandwich plates could be bent without failure when the clearance was larger than the thickness of the sandwich plate by three times.