High strain rate characteristics of 3-3 metal-ceramic interpenetrating composites

3-3 interpenetrating composites (IPCs) are novel materials with potentially superior multifunctional properties compared with traditional metal matrix composites. The aim of the present work was to evaluate the high strain rate performance of the metal-ceramic IPCs produced using a pressureless infiltration technique through dynamic property testing, viz. the split Hopkinson's pressure bar (SHPB) technique and depth of penetration (DoP) analysis, and subsequent damage assessment. Though the IPCs contained rigid ceramic struts, the samples plastically deformed with only localised fracture in the ceramic phase following SHPB. Metal was observed to bridge the cracks formed during high strain rate testing, this latter behaviour must have contributed to the structural integrity and performance of the IPCs. Whilst the IPCs were not suitable for resisting high velocity, armour piercing rounds on their own, when bonded to a 3 mm thick, dense Al₂O₃ front face, they caused significant deflection and the depth of penetration was reduced.     

Evaluation of effective elastic properties of 3D printable interpenetrating phase composites using the meshfree radial point interpolation method

ABSTRACT

Interpenetrating phase composites (IPCs) have recently been fabricated using three-dimensional (3D) printing methods. In a two-phase IPC, the two phases are topologically interconnected and mutually reinforced in the three dimensions. As a result, such IPCs exhibit higher stiffness, strength, and toughness than particle- or fiber-reinforced composites. In the current study, three unit cell models for the IPCs with the simple cubic (SC), face-centered cubic (FCC), and body-centered cubic (BCC) microstructures are developed using the meshfree radial point interpolation method. Radial basis functions with polynomial reproduction are applied to construct shape functions, and the Galerkin method is employed to formulate discretized equations. These unit cell-based meshfree models are used to evaluate effective elastic properties of 3D printable IPCs. The simulation results are compared with those based on the finite element (FE) method and various analytical bounding techniques in micromechanics, including the Voigt–Reuss, Hashin–Shtrikman, and Tuchinskii bounds. It is found that all of the simulation results for the effective Young's modulus and shear modulus fall between the Voigt–Reuss upper and lower bounds for each IPC considered, with the FE models predicting higher values than the meshfree models. In addition, it is seen that the SC microstructure leads to higher effective Young's modulus than the BCC and FCC microstructures. Furthermore, the numerical results reveal that the IPCs with the SC, BCC, and FCC microstructures can be approximated as isotropic materials (with the Zener anisotropic ratio varying between 0.9 and 1.0), with the BCC IPC being the most isotropic one, and the SC IPC being the least isotropic one among the three types of IPCs.     

Evaluation of incipient plasticity from interfaces between ultra-thin gold films and compliant substrates

Nanoindentation experiments were conducted for 30 nm-thick Au films on two types of substrates, polyimide (compliant) and glass (stiff), to clarify the dominant mechanics of incipient plasticity from the interface. A high resolved shear stress τ_r could be effectively applied to the Au/polyimide interface due to the compliant substrate, and plastic deformation was initiated at the interface. The critical resolved shear stress τ_crss at the interface was determined to have a value of 0.4 ∼ 0.5 GPa. On the other hand, in Au/glass, τ_r peaked within the Au film, and the maximum values were 1.1 ∼ 2.2 GPa depending on the tip radius, whereas the values of τ_r at the Au/glass interface were almost identical at 0.5 ∼ 0.7 GPa. Therefore, plastic deformation might be initiated from the Au/glass interface. The values of τ_crss for heterogeneous nucleation at the interfaces were smaller than that for homogeneous nucleation in the Au films.     

Production and Anisotropic Tensile Behavior of Resin‐Metal Interpenetrating Phase Composites

Metal‐polymer composites can be used to synthesize material properties. A variety of interpenetrating phase composites have been produced by spontaneously infiltrating porous short‐fiber preforms with unsaturated polyester resin under vacuum conditions. Porous preforms are fabricated by compacting and sintering short 304 stainless steel fibers from cutting stainless steel fiber ropes. Tensile experiments are conducted, and fractographs are examined via scanning electron microscopy. The results reveal that the tensile strength, elongation at maximum stress, and elasticity modulus of the IPCs increase with the increasing fiber fractions and exhibit anisotropy in different directions. The tensile strength and elongation at maximum stress are significantly improved compared with the consistent preforms. A nonlinear elastic behavior and sawtooth‐like fluctuation during yield deformation are noted. Compared with the through‐thickness direction, a higher tensile strength and larger elongation at maximum stress are observed in the in‐plane direction. Finer‐diameter fibers can improve the strength and increase the elongation at maximum stress. The tensile fracture surfaces show a mixture of brittle and plastic fracture characteristics.

     

Numerical prediction of elasto-plastic behaviour of interpenetrating phase composites by EFGM

Interpenetrating Phase Composites (IPCs) can be defined as multiphase materials in which each phase is three-dimensionally interconnected throughout the structure. No phase can be distinguished from the other based on the states of isolation and continuity; however both the phases contribute to the strengthening and improvement of the composite. The tensile and compressive yield and ultimate strengths of IPCs are much higher than a similar particulate composite due to their interpenetrating structure. This behaviour has been numerically simulated using element free Galerkin method. Ramberg–Osgood material model has been used to model the elasto-plastic behaviour of the composite. A progressive damage model has been used to simulate the failure mechanism of each phase. Three types of models have been proposed based on the treatment of the interface. The ultimate strength and the yield strength of IPC are obtained. The ultimate strength and the yield strength of the IPC depend largely on the properties, volume fraction and interpenetration of the constituent phases. The results of the present simulations are found in good agreement with the experimental results.     

泡沫铝-空心玻璃微珠/环氧泡沫复合材料压缩及弯曲力学性能

制备了泡沫铝、泡沫铝-环氧树脂及含有不同体积分数空心玻璃微珠(HGM)的三种泡沫铝-HGM/环氧泡沫互穿相复合材料(IPC)。通过一系列准静态压缩实验, 观察了其变形形貌, 研究了其弹性模量、屈服极限、比强度及比刚度等力学性能与HGM体积分数的关系。通过三点弯曲实验, 研究了IPC的弯曲极限载荷、弯曲弹性模量等性能, 分析了其断口形貌与材料结构的关系。实验结果表明: 四种IPC的力学性能均较纯泡沫铝有大幅度的提高, 其中, 泡沫铝-环氧树脂的压缩和弯曲力学性能最好。随着复合材料中HGM体积分数增加, IPC力学性能逐渐缓慢降低。     

Mechanical and elastic properties of transparent nanocrystalline TeO2-based glass-ceramics

Mechanical and elastic properties of transparent TeO₂-based glass-ceramics (15K₂O · 15Nb₂O₅ · 70TeO₂) consisting of nanocrystalline particles (each particle size: 40–50 nm) and showing optical second harmonic generation were evaluated by means of usual Vickers indentation and nanoindentation tests. The precursor glass has Vickers hardness H _v of 2.9 GPa, Young's modulus E of 54.7 GPa, the fracture toughness K _c of 0.25 MPam^1/2 and Poisson's ratio of 0.24. The transparent nanocrystalline glass-ceramic heat-treated at 420°C for 1 h has H _v = 3.8 GPa, E = 75.9 GPa and K _c = 0.34 MPam^1/2, and the opaque glass-ceramic heat-treated at 475°C for 1 h has H _v = 4.5 GPa, E = 82.9 GPa and K _c = 0.68 MPam^1/2, demonstrating that poor mechanical and elastic properties of the precursor TeO₂-based glass are improved through sufficient crystallization. The fracture surface energy, brittleness and elastic recoveries (about 44%) after unloading (the maximum load: 30 mN) of transparent nanocrystalline glass-ceramics are almost the same as those of the precursor glass, implying that the interaction among nanocrystalline particles is not so strong.     

Nanoindentation study of single-crystal NaTh2(PO4)3

The single crystals of sodium dithorium orthophosphate NaTh₂(PO₄)₃ (NThP) were studied by means of micro/nanoindentation. The NThP hardness was found to be Н_N = 8.76 ± 0.18 GPa and the elastic modulus Е_N = 144 ± 1 GPa. Microhardness anisotropy of the NThP crystal unequal faces is insignificant. The non-uniformity of plastic strain observed for the NThP is caused by fracture initiation and growth in the imprint. The average fracture toughness index (K_Ic) for the NThP is estimated to be equal to 0.56 MPa m^0.5.     

具有开孔泡沫骨架的双连续相复合材料弹性模量的理论预测

基于具有开孔泡沫骨架的双连续相复合材料(IPC)的细观结构,提出了一种十四面体弹性地基梁力学模型,结合最小势能原理推导了该IPC的弹性模量预测公式。根据文献给出的实验材料参数进行算例分析,结果表明,理论估算结果与实验值吻合良好,证明了该模型的有效性。在此基础上,进一步讨论了不同骨架材料体积含量和支柱截面形状对IPC弹性模量的影响。本文给出的半经验理论模型为表征具有开孔泡沫骨架的IPC的弹性性能提供了新思路,也为进一步预测IPC的强度性能和热物理性能奠定了基础。     

Shear bond strength and characterization of interfaces between electroformed gold substrates and porcelain

This study aimed to determine the effects of two different sandblasting conditions on the shear bond strength between electroformed Au substrates and porcelain, and characterize the interface between the Au substrate and porcelain. Electroformed Au specimens, 0.3 mm thick with a cap-like shape were prepared. The prepared specimens were then divided into two different groups and each group was sandblasted with a different size of alumina grains (100 or 250 μm) prior to dental porcelain application. Bonded specimens from each group were subjected to shear testing. After debonding, the fracture mode was analyzed by optical microscopy and SEM-EDX. One intact bonded specimen from each group was metallographically prepared to characterize the interfacial bonding by SEM-EDX and area scan analysis. The shear bond strength values (MPa) and standard deviations were 8.2 ± 1.8 and 9.1 ± 2.7 for the samples blasted with 100 and 250 μm alumina particles, respectively. No statistically significant difference was found between the two groups. In addition, no differences in fracture mode were found between the two groups. Qualitative analysis showed that, surprisingly, the Au substrate contained O, N, and P which might be related to the Au–sulfite electrolyte used in electroforming. As expected, the retained porcelain comprised Si, O, Al, Ca, Na and K. Mutual diffusion of Au, P, Si, Na, K and O without concentration gradients was found at the interface. Mutual ionic diffusion at the interface between ceramics and electroformed Au substrates (as opposed to mechanical interlocking) seems to be the most possible factor contributing to Au–ceramic bonding.     

Toughening of epoxy using core–shell particles

An epoxy resin, cured using an anhydride hardener, has been modified by the addition of preformed core–shell rubber (CSR) particles which were approximately 100 or 300 nm in diameter. The glass transition temperature, T _g, of the cured epoxy polymer was 145 °C. Microscopy showed that the CSR particles were well dispersed through the epoxy matrix. The Young’s modulus and tensile strength were reduced, and the glass transition temperature of the epoxy was unchanged by the addition of the CSR particles. The fracture energy increased from 77 J/m² for the unmodified epoxy to 840 J/m² for the epoxy with 15 wt% of 100-nm diameter CSR particles. The measured fracture energies were compared to those using a similar amount of carboxyl-terminated butadiene-acrylonitrile (CTBN) rubber. The CTBN particles provided a larger toughening effect when compared to CSR particles, but reduced the glass transition temperature of the epoxy. For the CSR-modified epoxies, the toughening mechanisms were identified using scanning electron microscopy of the fracture surfaces. Debonding of the cores of the CSR particles from the shells was observed, accompanied by plastic void growth of the epoxy and shell. The observed mechanisms of shear band yielding and plastic void growth were modelled using the Hsieh et al. approach (J Mater Sci 45:1193–1210). Excellent agreement between the experimental and the predicted fracture energies was found. This analysis showed that the major toughening mechanism, responsible for 80–90% of the increase in fracture energy, was the plastic void growth.     

Comparison study of silicon carbide coatings produced at different deposition conditions with use of high temperature nanoindentation

The elastic modulus and hardness of different silicon carbide (SiC) coatings in tristructural-isotropic (TRISO) fuel particles were measured by in situ high temperature nanoindentation up to 500 °C. Three samples fabricated by different research institutions were compared. Due to varied fabrication parameters the samples exhibited different grain sizes and one contained some visible porosity. However, irrespective of the microstructural features in each case the hardness was found to be very similar in the three coatings around 35 GPa at room temperature. Compared with the significantly coarser grained bulk CVD SiC, the drop in hardness with temperature was less pronounced for TRISO particles, suggesting that the presence of grain boundaries impeded plastic deformation. The elastic modulus differed for the three TRISO coatings with room temperature values ranging from 340 to 400 GPa. With increasing measurement temperature the elastic modulus showed a continuous decrease.     

Preparation and characterisation of ceramic-faced metal–ceramic interpenetrating composites for impact applications

This article accesses the impact performance of ceramic-faced, metal–ceramic interpenetrating composites (IPCs) produced in situ from infiltrating ceramic foams with a molten aluminium–magnesium alloy. The approach had two variations, viz., the production of a metal bond between a ceramic front face and backing IPC and the creation of a ceramic bond. The impact performance of metal-bonded IPCs was evaluated using both split Hopkinson’s pressure bar (SHPB) and depth of penetration (DoP) techniques. With a 4-mm thick Al₂O₃ front face and an 8-mm thick IPC backing, the DoP was zero. In one case, a sample survived fundamentally intact with only spall damage to the dense Al₂O₃ front face. The resulting damage was thoroughly assessed using a range of techniques, including polarized light microscopy, scanning electron microscopy (SEM), 3D MicroCT and transmission electron microscopy (TEM). The metal phase deformed as a result of the formation of large numbers of dislocations, whilst the ceramic phase accommodated the deformation via localised cracking. Metal bridges across the cracks formed, increasing the damage tolerance of the IPCs. The metal bond between the ceramic front face and the IPC was also observed to withstand the impact of the armour piercing rounds without any sign of debonding occurring.     

Mechanical properties and scratch resistance of filtered-arc-deposited titanium oxide thin films on glass

The mechanical properties and the scratch resistance of titanium oxide (TiO₂) thin films on a glass substrate have been investigated. Three films, with crystalline (rutile and anatase) and amorphous structures, were deposited by the filtered cathodic vacuum arc deposition technique on glass, and characterized by means of nanoindentation and scratch tests. The different damage modes (arc-like, longitudinal and channel cracks in the crystalline films; Hertzian cracks in the amorphous film) were assessed by means of optical and focused ion beam microscopy. In all cases, the deposition of the TiO₂ film improved the contact-mechanical properties of uncoated glass. Crystalline films were found to possess a better combination of mechanical properties (i.e. elastic modulus up to 221 GPa, hardness up to 21 GPa, and fracture strength up to 3.6 GPa) than the amorphous film. However, under cyclic sliding contact above the critical fracture load, the amorphous film was found to withstand a higher number of cycles. The results are expected to provide useful insight for the design of optical coatings with improved contact-damage resistance.     

A synthetic route for metal–ceramic interpenetrating phase composites

A novel synthetic route for metal–ceramic interpenetrating phase composites (IPCs) is proposed. The method excludes infiltration operations and eliminates the problem of closed pores and low wettability between ceramic and metal phase. We suggest using two-stage processing including preparation of composite powder precursors by reaction in a metal matrix and subsequent compaction of as-synthesized nanostructured powders. The appropriate choice of compaction technique allows obtaining dense nanostructured bulk IPCs. Bulk interpenetrating phase TiB₂–Cu nanocomposites were fabricated by Spark Plasma Sintering (SPS) and shock wave compaction of powder precursors.     

AFM indentation method used for elastic modulus characterization of interfaces and thin layers

Atomic force microscopy (AFM) is increasingly being used as a nanoindentation tool to measure local elastic properties of surfaces. In this article, a method based on AFM in force volume (force curve mapping) mode is employed to measure the elastic modulus distribution at the interface of a glass flake-reinforced polypropylene sample and at a lead-free Cu–solder joint. Indentation arrays are performed using a diamond AFM tip. The processing of experimental AFM indentation data is automated by customized software that can analyse and calibrate multiple force curves. The analysis algorithm corrects the obtained force curves by selecting the contact point, discarding the non-contact region and subtracting the cantilever deflection from the measured force curve in order to obtain true indentation curves. A Hertzian model is then applied to the resulting AFM indentation data. Reference materials are used to estimate the tip radius needed to extract the elastic modulus values. With the proposed AFM measurement method, we are able to obtain high-resolution maps showing elastic modulus variations around a composite interface and a Cu–solder joint. No distinct interphase region is detected in the composite case, whereas a separate intermetallic layer (1–2 μm thick) of much higher Young’s modulus (~131 GPa) than Cu and solder material is identified in the Cu–solder joint. Elastic modulus results obtained for the Cu (~72 GPa), solder (~50 GPa) and glass (~65 GPa) materials are comparable to the results obtained by instrumented indentation [~73, ~46 and ~61 GPa], which accentuates the potential of this method for applications requiring high lateral resolution.     

Compressive strength,modulus of elasticity,and water permeability of inorganic polymer concrete

Inorganic polymer concretes (IPCs) were produced from rice husk–bark ash (RHBA) combined with fly ash (FA) as a cementitious raw material. Six different mixtures were used to study the properties of IPC. Since RHBA is rich in silica material, varying the ratio of FA to RHBA results in differing SiO₂/Al₂O₃ ratios. To keep the SiO₂/Al₂O₃ ratio constant, the ratio of FA to RHBA was fixed at 80:20 by weight. High concentration sodium hydroxide solution and sodium silicate solution were used as a liquid component of the concrete mixture. The mixing and curing of these inorganic polymer concretes were performed under ambient conditions. Compressive strength, modulus of elasticity, and water permeability of the IPCs were investigated at specified intervals up to 90 days. The results showed that the compressive strength, modulus of elasticity, and water permeability of IPCs depend on the mix proportions, especially the solution to ash (S/A) ratio and the paste to aggregate (P/Agg) ratio. Moreover, the results showed that the water permeability and the elastic modulus of IPCs were significantly related to their compressive strength.     

More on the behavior of soda lime glass under shock loading

A series of plate impact experiments with soda-lime glass specimens was performed in order to further investigate the complex behavior of this material in the 0–8 GPa range of shock loading. Using commercial manganin gauges we followed the stress histories and their different shapes as the stresses increase from 3.5 to about 8.0 GPa. In particular, we find that there are meaningful differences between the shapes of these signals at pressures below about 4.0 GPa, in between 4.0 and 6.0 GPa and above 6.0 GPa. We also gather more data on the fractured glass behind the fracture wave front, from our measured stress histories, and offer a new way to determine the Hugoniot elastic limit of this material, as well as other brittle solids.     

Failure behavior of Cu–Ti–Zr-based bulk metallic glass alloys

Microstructure fracture and mechanical properties of Cu-based bulk metallic glass alloys were investigated. Centrifugal casting into copper molds were used to manufacture basic Cu₄₇Ti₃₃Zr₁₁Ni₉, and modified Cu₄₇Ti₃₃Zr₁₁Ni₇Si₁Sn₁ alloys. Although the alloys show an amorphous structure, TEM images revealed the formation of nanoparticles. At room temperature compression tests reveal fracture strength of 2000 MPa, elastic modulus of 127 GPa, and 1.8% fracture strain for the unmodified basic alloy. Whereas the modified alloy exhibits a fracture strength of 2179 MPa, elastic modulus reaches 123 GPa, and 2.4% fracture strain. So, with the addition of 1 at.% Si and Sn, the fracture strength improves by 9% and the fracture strain improves by 25%, but the fracture behavior under compression conditions exhibits a conical shape similar to that produced by tensile testing of ductile alloys. A proposed fracture mechanism explaining the formation of the conical fracture surface was adopted. The formation of homogeneously distributed nano-size (2–5 nm) precipitates changes the mode of fracture of the metallic glass from single to multiple shear plane modes leading to the conical shape fracture surface morphology.     

Influence of the addition of thermoplastic preformed particles on the properties of an epoxy/anhydride network

An anhydride/epoxy system is modified by the introduction of thermoplastic microparticles (ORGASOL®). The influence of the presence of polyamide (PA) particles is evaluated on the reactivity of the epoxy/anhydride system below the melting temperature of the thermoplastic. Networks containing various amounts of polyamide are prepared using a cure schedule in order to keep the PA particles below their melting point. Both thermomechanical and mechanical behaviours (glass transition temperature, elastic, plastic and fracture properties) are studied and discussed as a function of the polyamide nature, the particle content and the adhesion between the particles and the matrix.