Interfacial Shear Research Articles

Temperature-Dependent Post-Cyclic Mechanical Characteristics of Interfaces between Geogrid and Marine Reef Sand: Experimental Research and Machine Learning Modeling

The mechanical response of the marine reef sand–geogrid (RG) interface can be influenced by a high-temperature climate, grain size, and variable stress environments. These factors are critical to the effectiveness of geogrid reinforcement in reef sand engineering. However, there are few studies on the influences of grain size, temperature, and stress history on the mechanical characteristics of RG interfaces, with most studies centering on the influence of single factors on the mechanical characteristics of RG interfaces. In this paper, based on self-developed temperature-controlled large interface shear equipment, a series of before/post-cyclic shear tests were carried out on RG interfaces in the temperature range of 5–80 °C. The impact of different reef sand grain sizes on the RG interface was explored (S1: 1–2 mm; S2: 2–4 mm). It was shown that temperature and grain size had significant influences on the mechanical characteristics of the RS interface. Compared with the S1 RG interfaces, the S2 RG interfaces had higher sensitivity to temperature changes with respect to the before/post-cyclic maximum shear strength. Moreover, in comparison to the before-cyclic shear strength, the post-cyclic maximum shear strength is more responsive to temperature changes. The before/post-cyclic maximum shear strength of the S2 RG interfaces was greater than the maximum shear strength of the S1 RG interfaces as the temperature changed. Based on the results of physical tests, a machine learning model containing 450 datasets was constructed, which can accurately predict the shear strength of the RG interface.

Mesoscale modeling of new-to-old concrete interface under combined shear and compressive loads

A mesoscale model of new-to-old concrete interface under combined shear and compressive loads is established, and a parameter study is conducted to evaluate the influence of interface roughness, bond strength, and fracture energy. The mesoscale model is numerically generated using a random aggregate technique, in which the number of aggregates is calculated using the Fuller grading curve and Walraven formula and the aggregates are randomly placed using the Monte Carlo simulation. The concrete damaged plasticity model is employed to simulate the mechanical behaviors of new and old mortars, as well as the interfacial transition zone between the mortar and aggregate. The linear elastic model is utilized to simulate the behavior of aggregates, while the cohesive-friction model is employed to represent the behavior of new-to-old concrete interface. The effect of interface roughness, bond strength, and fracture energy on the interface shear strength and post-peak shear strength using the double-shear test specimens is investigated. The results indicate that increasing the roughness of old concrete surface leads to significant increases in both the interface shear strength and post-peak shear strength, but the larger interface roughness is not necessarily better. As the interface bond strength increases, the interface shear strength remains the same, whereas the post-peak shear strength shows a large increase with the lower interface roughness. Moreover, the interface fracture energy imparts the minimal influence on the interface shear strength and post-peak shear strength, but the higher interface fracture energy can improve the overall constitutive behavior of new-to-old concrete interface if the roughness of old concrete surface is low. The numerical mesoscale model presented can provide the theoretical guidance and technical support for effective design and construction of new-to-old concrete interface and structures.

A parametrized continuum constitutive model for reinforced thermoplastic composites with mechanically interlocked interface

Reinforced thermoplastic composites (RTPC) exhibit weak interfacial strength due to the low surface energy of the polymer matrix. Recently, a concept of controlled mechanical interlocking was introduced that showed significant improvement in the interfacial shear strength with pure mechanical interlocking and no chemical bond/friction. In this paper, a parametrized continuum material model is developed through computational homogenization for an E-glass/polypropylene (PP) composite system with a mechanically interlocked interface. Such parametric models not only elucidate the effects of the microstructural parameters on the mechanical behavior of the material but also enables the optimization of the composite at the microstructure level.

Ultra-strong bonding of 30-wt% GF/PET-A2024 aluminium alloy via collaborative promotion of ultrasonic-assisted FeCl3+N2H4 corrosion and the coordination bonds by Zr4+

Enhancing the bonding strength between metals and polymers is advantageous for hybrid structures used in aerospace and power electronics applications. This study, conducted for the first time, involves the preparation of multi-scale “honeycomb-meteorite crater” morphologies on the surface of A2024 aluminium alloy through a multi-step ultrasonic-assisted corrosion treatment. The ultrasonic-assisted FeCl3/N2H4 corrosion process increased the interfacial tensile shear strength of a 30-wt% glass fibre reinforced PET-A2024 aluminium alloy joint (expressed as 30-wt% GF/PET-A2024) to 32.0 MPa. Coating Zr4+ substantially enhances the hydrophilicity of the A2024 surface; however, the coordination bonding effect of Zr4+ can only be activated after prolonged heat treatment (100 °C, 3 h). With the combined effects of multi-scale mechanical interlocking and coordination bonding of Zr4+, the tensile shear strength of the 30-wt% GF/PET-A2024 joint can reach 56.5 MPa, surpassing existing works by a significant margin. Experimental results and Density Functional Theory (DFT) calculations demonstrate that the optimal concentration for Zr4+ treatment is 1.5 wt%. Excessive Zr4+ would lead to ion-dipole interactions, which diminish the interface bonding strength; when the concentration of Zr4+ is 2 wt%, The joint strength dropped sharply to 39.1 MPa. This study provides a comprehensive discussion on ultrasonic-assisted corrosion and the effect of Zr4+, offering valuable insights for future research aimed at enhancing the interfacial bonding strength between polymers and metals.

Characterization and mechanism analysis of interfacial shear strength between individual aramid fiber and epoxy by oxygen plasma treatment at elevated temperatures: Experiment and simulation

The weak adhesion between aramid fibers Ⅲ and the resin matrix, due to its smooth surface and high inertness of the fibers. This property restricts the mechanical properties of the composites in high temperatures environments. This work describes the treatment of aramid fibers Ⅲ with oxygen plasma to introduce reactive oxygen-containing functional groups onto fiber surface. The analysis focused on the impact of interfacial friction and interfacial wettability on the transfer of load across composites at various temperatures. According to the X-ray photoelectron spectroscopy (XPS) analysis, the fiber surface showed an increase in the number of active groups after plasma treatment. In addition, two new oxygen-containing functional groups -C-O- and -O-CO appeared. The use of Scanning Electron Microscopy (SEM) and atomic Force Microscopy (AFM) showed that the plasma treatment has an etching effect on the fiber surface and increases the roughness of the fiber surface. Furthermore, after plasma treatment, the fibers adhered to the resin matrix through hydrogen bonding and π-π bonding. The utilization of this technique led to a significant enhancement in the interfacial properties of monofilament composites across various temperature ranges. The IFSS of plasma-treated aramid fiber Ⅲ/EP exhibited increases of 38 % at the test temperature of 25℃. Surprisingly, the IFSS of plasma-treated aramid fiber III/EP exhibited a significant increase of 52 % at the test temperature of 120℃. In this paper, COMSOL software was utilized to simulate the IFSS before and after plasma treatment at different temperatures. Mechanistically explains the effect of temperature on the interfacial mechanical properties of composites.

Peak and Residual Shear Interface Measurement between Sand and Continuum Surfaces Using Ring Shear Apparatus

This study uses a ring shear apparatus to measure the interface shear stress between five types of sand and three surfaces: steel, PVC, and stone. Experiments were conducted under normal stresses of 25, 50, and 100 kPa at a constant shear rate of 0.5 mm/min. The research examines the impact of various sand properties, including particle size distribution, median particle size, particle shape, and initial density, as well as the surface roughness and hardness of continuum materials. The results show that interface shear strength is significantly influenced by the mechanical interlock between sand particles and surface asperities, which is affected by the normalized roughness and hardness of the materials. Machine learning models, including Multiple Linear Regression and Random Forest Regression, were used to predict peak and residual shear strengths, demonstrating high accuracy. Additionally, an empirical equation was generated using eight input parameters, considering the peak and residual interface shear strength as outputs.

AlCrTaTiZr-based high entropy alloy nitride coatings on stainless steel substrates: Characterization and microscale tension testing

High entropy alloy nitride coatings promise improved mechanical properties and are under current investigation for a range of applications. In this work, we report deposition of high entropy alloy nitride coatings on 316 stainless steel substrates by inductively coupled plasma assisted dc magnetron reactive sputtering of nominally equiatomic AlCrTaTiZr alloy targets. Characterization of coating composition and structure was carried out through X-ray photoelectron spectroscopy, Rutherford backscattering spectrometry, X-ray diffraction, and scanning/transmission electron microscopy. Mechanical testing was conducted through instrumented nanoindentation, interfacial shear loading through micropillar compression, and tension loading of coated microscale tensile bars in a scanning electron microscope. Microscale tension testing offers a potential avenue to assess the limiting shear strength of the coating/substrate interface, as well as the level of cohesion within the coating. The present study indicates that microscale tension tests yield results consistent with macroscale testing, while avoiding the need for multiple macroscale specimens. The present results suggest that cohesion of the high entropy alloy nitride coating and limiting shear strength of the coating/steel interface both increase with increasing substrate bias voltage during deposition, and that these coatings may be more adaptive to increased levels of ion bombardment during deposition without inducing excessive residual stresses.

Influence of the ribbed steel core on the inner interface mechanical behavior of the ESDCM pile

By virtue of the high strength, cost-efficiency and green construction, the expanded stiffened deep-cement-mixing (ESDCM) piles with steel cores own a great prospect to be applied for soft soil treatment in coastal and riverside regions. The dual-interface feature is a crucial factor affecting the bearing capacity of the ESDCM piles. However, the confining pressure characteristics of pile cores and the interface characteristics of steel pipe-soil-cement are unclear, limiting the practical application of ESDCM piles. Hence, in this work, we investigate the mechanical characteristics of the inner interface of ESDCM piles with steel cores via confining pressure transfer test and inner interface shear tests. The results demonstrate that the soil-cement column can withstand over 90 % of the confining pressure exerted on the outer interface, suggesting that the pile core may not be affected by confining pressure. Model piles with different steel cores have different interface failure modes, which can be described using either a three-segment or two-segment constitutive equation. Changing the inner interface structure has been proven to be a highly efficient pathway for enhancing the bearing capacity and adhesion conversion factor of the ESDCM pile. Compared with the smooth steel cores, the adhesion conversion factor can be reinforced up to 114.3 % by employing ribbed steel cores. Then, a model-pile bearing capacity calculation formula was established and verified for reliability. Moreover, the formula of a single pile based on inner interface shaft resistance was further proposed in combination with the actual operating conditions. This study highlights the mechanical characteristics of the inner interface of ESDCM piles, which guides engineering design and construction.

Warpage control and interface characteristics of Ti/Al composite plates by differential temperatures rolling with mobile induction heating

This study addresses the issue of warping and low interfacial bonding strength in composite plates due to uncoordinated deformation during the rolling of titanium/aluminum composites. By adopting mobile induction heating with differential temperature rolling composite technology, heated titanium plates and room-temperature aluminum plates were successfully rolled into composites. The results show that when the titanium plate is heated to 500–900°C, the warpage of the titanium/aluminum composite plates first decreases and then increases, while the interface shear strength first increases and then decreases. It is particularly emphasized that the rolled composite plates is straight at 800°C, the Ti6O oxide layer formed on the titanium plate surface exhibits excellent adhesion to the substrate, while displaying susceptibility to cracks during the rolling process, allowing fresh aluminum metal to be squeezed into the cracks to form a mechanical mesh and an atomic bonding diffusion layer occurs due to the fresh metal contact between titanium and aluminum within the crack, thereby resulting in the composite plates exhibiting optimal shear strength. The findings verify the preliminary feasibility of the proposed novel rolling process and provide a novel solution for prepared titanium/aluminum composite plates, which is an important step for future fabrication and applications of composite plates.

Wrinkling suppression in cryogenic forming of high-strength Al-alloy ultra-thin shells by controlling interface shear stress

Avoiding wrinkling defects is extremely difficult in the sheet metal forming of ultra-thin components made from high-strength aluminum alloys. A novel cryogenic forming is thus proposed for solving this very challenging problem, wherein a thicker cladding blank is stacked above the thinner target blank to establish interface shear stress for reducing the hoop compressive stress, so that the critical wrinkling stress is increased. The enlarged radial deformation is transferred and withstood by the increasing hardening and ductility at cryogenic temperatures. The wrinkling suppression mechanism is revealed through mechanical and numerical analyses. Systematic experiments were conducted for studying the feasibility of high-strength AA7075 in cryogenic forming with different stacking sequences of cladding and target blanks, cladding blanks including three material strength levels (AA1060-O, AA5052-O, and SUS-304), two thicknesses (3.0, and 2.0 mm), and blank-holder forces. The effects of the cladding blank and blank-holder forces were clarified as reflected by forming defects, thickness, and strain distributions. The mechanical and numerical analyses can indicate that contact pressure can be produced by the wrinkling tendency of thinner target blank and limitation of cladding blank to wrinkling, which is accompanied by a decrease in the hoop compressive stress and increase in the critical wrinkling stress. Therefore, applying a relatively thicker blank on the punch side can prevent the wrinkling of ultra-thin components. The wrinkling tendency decreases with increasing strength and thickness of the cladding blank, which results in an increase in deformation or even splitting, which can be solved by the cryogenic temperature. The thickness of the cladding blank can be reduced by increasing the blank-holder force, which further reduces the material cost. AA5052-O, which has a strength similar to that of the target blank, is more suitable as a cladding blank for AA7075-W because the balance preventing wrinkling, improving thickness uniformity, and controlling the forming force. A Φ200 mm hemispherical shell with an initial thickness of 0.3 mm was formed successfully, and the corresponding thickness-to-diameter ratio reached 0.8‰, which almost increased one time on the basis of direct cryogenic forming. This new approach can be used for fabricating ultra-thin components from high-strength aluminum alloys.

Cellulose nanofiber-induced metal–organic framework “armor” for the fabrication of carbon fibre composites with enhanced mechanical properties and electrical conductivity

Metal-organic frameworks (MOFs) possess significant potential in enhancing the interfacial performance of composites owing to their exceptional skeletal structures and substantial specific surface area. Herein, we prepared typical conductive MOFs (Ni-HHTP, HHTP = 2, 3, 6, 7, 10, 11-hexahydroxybenzene) at the interface by in situ synthesis using cellulose nanofibers (CNFs) assembled on the surface of carbon fibres (CFs) as precursors. CNFs can not only act as a smart cushion to promote stress release but also provide abundant oxygen-containing functional groups, such as hydroxyl and carboxyl groups, which can facilitate the growth of MOF on the surface of CFs. Furthermore, MOFs with porous structure and large specific surface area increase the interphase region for interfacial load transmission. The CF composites prepared using this strategy exhibited improvements in interlaminar shear strength (ILSS), interfacial shear strength (IFSS), flexural strength and flexural modulus by 57.9 %, 54.9 %, 35.1 % and 46.7 %, respectively. Additionally, the electrical conductivities of the composites in both thickness and in-plane directions were 1.04 × 10−4 S/cm and 7.3770 S/cm, respectively, which was attributed to the MOFs on the surface of the fibres facilitating the formation of good conductive channels between the fibres and resin. This study proposes an advanced interfacial modification approach to prepare CF composites with excellent mechanical and electrical conductivity properties.

Experimental and analytical investigation of the shear behavior of steel-bamboo composite I-beams with composite connections

In steel-bamboo composite beams, the debonding failure and slip behavior of steel-bamboo pure bonding interfaces at the flanges often lead to premature failure of beams and underutilization of material strengths. Therefore, a novel steel-bamboo composite I-beam with composite connections was presented in this study, in which the pure bonding interfaces at the beam's flanges were reinforced by self-tapping screws (STSs). 13 beams were designed and fabricated with interface type, shear span-to-depth ratio, height-to-thickness ratios of bamboo and steel at the web, and width-to-thickness ratio of steel at the flange as main parameters. Then, shear tests and theoretical analysis were performed to evaluate the beam's shear behavior. The results indicated that the debonding failure and slip behavior of the beams were effectively limited, and the shear resistance, deformation capacity, and ductility were significantly improved. The shear resistance of beams was improved by reducing the shear span-to-depth ratio, height-to-thickness ratios of the bamboo and steel at the web, and steel flange width-to-thickness ratio. Finally, the developed analytical models can be concluded to be used to accurately predict the interfacial shear stress at the beam flanges in the serviceability limit state (SLS) and ultimate shear capacity of the beams.

Effect of hygrothermal aging on the friction behavior and wear mechanism of the multi-filler reinforced epoxy composites for coated steel

Polymer-based composites for steel structure coating are an effective strategy to improve tribological properties and service durability under hygrothermal aging conditions. In the present paper, epoxy resin was improved by mechanical reinforcement and frictional lubrication fillers, and a kind of multi-filler reinforced epoxy composite (MFREC) was successfully prepared. Water uptake behavior, mechanical and thermal property evolution, friction behavior and wear mechanism as well as micro-topography analysis of MFREC under hygrothermal aging were conducted and discussed in detail. The research results showed that the water uptake curve of MFREC after distilled water and 5 wt% NaCl water solution immersions confirmed the two-stage diffusion model, where the quasi-equilibrium water uptakes were 4.23% and 3.67%, respectively. Additionally, the fundamental reason for the degradation of the mechanical and thermal properties of MFREC was the hydrolysis of the resin and the de-bonding of the fillers/matrix interface. The interface shear strength of MFREC adhesive and steel gradually decreased with the hygrothermal aging, but did not lose the bonding property, because the uniformly dispersed multi-fillers can fill the internal defects of the matrix and prolong the crack propagation path to block the effect. Before hygrothermal aging, MFREC had excellent friction and wear resistance compared to resin matrix, especially under water lubrication conditions. The anti-wear rate of MFREC increased by up to 59.6% compared to the room temperature dry test environment due to the coupling effects of the water lubrication and anti-friction characteristics of modified fillers. Hygrothermal aging had little effect (＜12%) on the friction coefficient of MFREC, but the anti-wear properties decreased significantly, especially the Ws increased by 255.1% under the 60 °C immersion condition. Because the degradation of thermal/mechanical properties was not enough to resist the high shear stress of the steel ball, leading to severe fatigue wear.

Application of high-pressure homogenization-assisted pH-shift to enhance techno-functional and interfacial properties of lentil protein isolate

High-pressure homogenization (HPH) is a promising physical non-thermal approach to improve protein techno-functionality. This study aims to examine the effects of HPH on the lentil proteins through the perspective of the interfacial adsorption mechanism. The impact of HPH treatment on lentil protein isolate (LPI) at varying pressure levels (0–150 MPa) was determined using several analytical techniques, including SDS-PAGE, FTIR, solubility, and techno-functional properties (foaming and emulsifying properties), alongside analyses of interfacial tension and interfacial shear rheology at the o/w and a/w interfaces for two pH values (2.0 and 4.5). Results reveal that HPH treatment up to 100 MPa effectively unfolds lentil proteins by disrupting disulfide-bonded subunits into lower molecular weight fractions and unfolding highly-ordered secondary structures into random coils. LPI's capacity to produce emulsions and foams was found to be enhanced concurrently with these physicochemical changes, particularly at pressures up to 50 MPa. The findings aligned with the interfacial tension and shear rheology analyses, which show that proteins can form interfacial viscoelastic films on both o/w and a/w interfaces. Furthermore, the interfacial behavior of LPI and the effect of HPH on the interfacial behavior were found to be pH-dependent. The lower interfacial tension and the higher interfacial viscoelastic moduli (G′ and G″) were recorded at 50 MPa and 0 MPa at pH 2.0 and 4.5, respectively. These results stated that the effects of the HPH on the technofunctionality of LPI can be further enlightened by investigating the interfacial adsorption kinetics.

Study on the mechanism of freeze-thaw cycles on the shear strength of geogrid-sand interface

The geogrid-soil interface characteristic is a critical factor influencing the behavior of reinforced soil structures. In seasonal frozen regions, the shear strength of the geogrid-soil interface fluctuates periodically with temperature, necessitating consideration of freeze-thaw cycle effects during engineering design. In this study, a series of large-scale direct shear tests were conducted to investigate the geogrid-sand interface behavior under different freeze-thaw cycles. The mechanism of the evolution and variation of the geogrid-sand interaction was discussed based on test results and the associated mesoscopic analysis. The results indicate that freezing enhances the shear strength of the geogrid-sand interface, whereas freeze-thaw cycles reduce the geogrid-sand interface shear stress. The cohesion and friction angle of the geogrid-sand interface decreased as the number of freeze-thaw cycles increased, but tended to stabilize after several freeze-thaw cycles. The influence of freeze-thaw cycles on the tensile strength and elongation of the geogrid was insignificant. Internal changes in sand during freeze-thaw cycles were considered as the key issue that led to the deterioration of the geogrid-sand interface. Furthermore, considering the interface cohesion and normal stress, the influence of freeze-thaw cycles on the interaction coefficient k between geogrid and soil was analyzed, which is referable for the design and application of reinforced soil engineering in cold regions under similar conditions.

A novel coaxial heat pipe with an inner vapor tube for cooling high power electronic devices

Improving heat transfer limit of heat pipe is important for their application in high-power equipment system. Shear stress at the liquid–vapor interface affects the heat transfer capacity of heat pipe. In this study, a novel coaxial heat pipe is designed to eliminate vapor entrainment from interfacial shear stress for the first time. An inner thin-walled tube is sintered with the powder wick in the adiabatic section by one-step sintering process. The effects of filling ratio and powder size of sintered wick on the thermal performance of coaxial heat pipe are investigated experimentally. The results indicate that the optimal powder size range for the sintered wick of coaxial heat pipe is 106–125 μm, while the optimal filling ratio is about 125 %. It means that the sintered wick with 106–125 μm powder can achieve better trade-off between capillary performance and permeability. The coaxial heat pipe can operate at heat loads of 70 ∼ 140 W with the total thermal resistance less than 0.06 °C /W. Moreover, compared with the normal heat pipe, the heat transfer capacity of coaxial heat pipe is increased by 57 %, while the evaporation temperature is decreased by 9.6 ∼ 19.1 °C and the total thermal resistance is decreased by 41 %∼320 %. The inner tube can improve the replenishment efficiency of working liquid by eliminating interfacial shear stress, resulting in the significant heat transfer improvement. The design of coaxial heat pipe is an effective and low-cost solution to improve the thermal performance of heat pipe.

The selection mechanism of mineral bridges at the interface of stacked biological materials for a strength-toughness tradeoff

The strength-toughness tradeoff in biological materials such as nacre and bone is essentially due to their stacked microstructures formed by hard and soft phases. In some of these materials, purely soft phase acts as interface layers linking hard phases (platelets), while in some others, hard-phase bridges exist in the soft phase to form a hybrid interface. In order to disclose the selection mechanism of such different interface structures in biological materials, a novel shear-lag model with an interface consisting of alternatively distributed elasto-plastic (soft) and brittle-elastic (hard) segments is proposed. Using this model, solutions of tensile stress and tensile displacement in hard platelets and shear stresses in soft and hard interfacial segments are analytically achieved. Effects of the hybrid interface on the effective mechanical performances of the composite are analyzed, the results of which are well consistent with the existing experimental observations in biocomposites and bio-inspired composites. The most important finding is that the fracture strain of the soft phase has a decisive effect on the selection of a purely soft-phase interface or a hybrid interface of hard and soft phases in stacked biological materials in order to realize a tradeoff between strength and toughness. When the failure strain of the soft phase is relatively small, such as nacre, the purely soft-phase interface is too weak to transfer enough load to the platelet, and hard bridges are necessarily required to reinforce the interface and guarantee an efficient load transfer. When the soft phase has a sufficiently large failure strain, such as bone, the purely soft-phase interface is tough enough to sustain a large shear deformation, realizing an efficient load transfer and adequate utilization of all constituents, while an additional hard bridge is not conducive to the composite toughness due to its reducing effect on the interfacial shear deformation. The results not only help people gain a deeper understanding of the secrets behind the construction of different interfaces in biological materials, but also provide useful guidance for interface optimization design in strong and tough artificial materials.

Effects of recrystallization on interfacial microstructure evolution and shear strength of TiAl alloy joints

The effects of dynamic recrystallization (DRX) and post-bonding heat treatment (PBHT) on the interfacial microstructure evolution and mechanical properties enhancement of Ti-43Al-4Nb-1Mo-0.2B alloy joints, subjected to various bonding parameters, were thoroughly investigated through detailed microstructural characterization and shear performance tests. A strip-like DRX area was observed at the interface when bonding at 1100 °C, ≥30 MPa, for 60 min. Equiaxial- γ grains underwent discontinuous dynamic recrystallization during the bonding process, and tended to form flat grains parallel to the lamellae direction during recrystallization annealing (1000 °C/6 h) owing to the hindrance imposed by the lamellae on both sides. The orientations of lamellae on the both sides of bonding interface affects the lamellae's stress distribution and deformation behavior at the bonding interface, subsequently influencing the DRX behavior and the width of the DRX zone. Static recrystallization (SRX) during the recrystallization annealing treatment can eliminate bonding defects of joints bonding at lower pressures or temperatures. Optimal joints with fully lamellar interfacial microstructure and excellent shear properties can be obtained through single-α phase annealing treatment. Lamellae microstructure tailored through PBHT can significantly enhance the quality of joints, attributed to the homogeneity of the microstructure between the interface and matrix. The highest shear strength of 478 MPa, accounting for 82 % of the matrix strength, was obtained under the bonding parameters of 1100 °C/30 MPa/60 min-1290 °C/15 min. This work provides important DB process parameters for fabricating of complex structural parts of TiAl alloy.

Spatiotemporal Filter Velocimetry With Arbitrary-Shaped Measurement Region For Accurate Measurement In The Vicinity Of A Boundary

Viscous stress at a boundary or an interface is a source of drag acting on a body or a fluid particle and therefore its measurement is of great importance for understanding the motion of the body or the fluid particle. In this study, spatiotemporal filter velocimetry (SFV: Hosokawa & Tomiyama, 2012) is extended to arbitrary quadrilateral measurement areas fitted to an interface shape for accurate measurement of flow about a deformed drop, and it is applied to flows about single drops of glycerol-water solution falling in stagnant silicon oil under clean and contaminated conditions. Figure 1 shows the trajectories of tracer particles and the measured velocity distributions. No separation is observed for the spherical and ellipsoidal drops. On the other hand, the stagnant region is observed in the dimple region of the tail of the cap drop. These results clearly indicate that the flow about the deformed drop is successfully measured by SFV with arbitrary quadrilateral measurement areas. Figure 2 shows the trajectories of tracer particles and the measured velocity distributions of single ellipsoidal drops in clean and contaminated systems. Triton X-100 was used as the surfactant and its concentration C in the drop ranges from 0.0 to 0.1 mol/m3 . The drop tail becomes flat and then slightly dimpled shape, and the internal circulation becomes weak as C increases. The internal circulation remains even at the high surfactant concentration condition under which the internal circulation in single spherical drop is fully damped (Hosokawa et al., 2017). We also evaluate interfacial velocity, interfacial shear stresses, the Marangoni stress and surfactant concentration at the interface from measured velocity distributions in the vicinity of the interface. As a result, we confirmed that SFV enables us to measure velocity distribution about a single deformed drop and enables us to evaluate interfacial velocity, interfacial shear stresses, the Marangoni stress and surfactant concentration at the interface.

Identification of interfacial strength between carbon fiber and epoxy matrix in CFRP laminates using pulse laser spallation method

Carbon fiber reinforced plastics (CFRP) have high specific strength and specific stiffness and are used in various fields such as aircraft, space structures, automobiles, and other transportation equipment. Since the internal structure of CFRP is very complex, it is very difficult to define failure criteria when external loads are applied. Various methods have been proposed to evaluate the interfacial shear strength between carbon fiber and resin matrix, such as microbond test, rupture test, and pull-out test, but currently no effective method has been proposed to evaluate the tensile strength of the CF/resin interface. In this study, we applied the pulsed laser spallation method, which has been confirmed to be effective for evaluating the adhesion strength of thin films and coating films on substrates, to the evaluation of CFRP. A finite element method based on the Laplace transform was used for the numerical analysis of the unsteady elastodynamic problem. The macroscopic stresses generated by ultrasonic waves excited by pulsed laser irradiation were calculated by inverse analysis using a transfer function with the displacement history of the back surface of the CFRP specimen as supplementary information. Microscopic stresses at the fiber/resin interface were evaluated by the homogenization method, taking into account the effects of fiber arrangement, distance between fibers, and molding residual stress in unidirectionally reinforced CFRP laminates. As a result, this series of investigations revealed that the vertical interfacial stress is dominant with respect to the strength of the fiber/resin interface with the strength of about 54MPa.