Interfacial Stress State Research Articles

Numerical analysis of the effect of ice-metal interface stress singularity on bonding failure

ABSTRACT The formation of ice on the surface of the metallic casing of high-end equipment poses a potential threat to its operational safety and stability. One important factor that contributes to bonding failure at the ice-metal interface is stress concentration. This paper aims to investigate the effect of stress concentration on the bonding failure behavior at the ice-metal interface through numerical analysis. First, the forms of bonding failure are categorized. Afterwards, the stress distribution state at the corners of the ice-metal interface is determined by the interfacial stress singularity. Finally, numerical analysis is carried out to investigate the thermal stress distribution law at the corners of the interface during the cooling process of the ice-metal bonding, so as to elucidate the induced mechanism of the interfacial stress state on the bonding failure. This study can provide some reference and guidelines for the study of bonding failure at the ice-metal interface.

Improvement and Evaluation of a Device That Determines the Interfacial Shear Strength of Carbon Fiber/Polyphenylene Sulfide Composites.

This study improved homemade apparatus for characterizing the interfacial shear strength (IFSS) of carbon-fiber-reinforced polyphenylene sulfide (PPS/CF) composites. The upgraded generation II experimental device includes a newly developed experimental clamp for samples, as well as testing systems. Compared with the initial generation I apparatus and the commercial Toei instrument, the generation II device is easier and more efficient to operate. The average interfacial adhesion values obtained using these devices were consistently approximately 40 MPa, with relatively low data scatter, showing excellent repeatability and applicability during microbond tests. Notably, the generation II experimental device was equipped with an additional high-frequency data-capturing tool to identify the debonding peak force more precisely, which demonstrated a higher interfacial shear strength of 42.81 MPa during testing. Therefore, the new instrument was able to reflect the change in the interfacial stress state during the interface debonding process more accurately and reliably.

Tuning the interlayer microstructure and residual stress of buffer-free direct bonding GaN/Si heterostructures

The direct integration of GaN with Si can boost great potential for low-cost, large-scale, and high-power device applications. However, it is still challengeable to directly grow GaN on Si without using thick strain relief buffer layers due to their large lattice and thermal-expansion-coefficient mismatches. In this work, a GaN/Si heterointerface without any buffer layer is fabricated at room temperature via surface activated bonding (SAB). The residual stress states and interfacial microstructures of GaN/Si heterostructures were systematically investigated through micro-Raman spectroscopy and transmission electron microscopy. Compared to the large compressive stress that existed in GaN layers grown on Si by metalorganic chemical vapor deposition, a significantly relaxed and uniform small tensile stress was observed in GaN layers bonded to Si by SAB; this is mainly ascribed to the amorphous layer formed at the bonding interface. In addition, the interfacial microstructure and stress states of bonded GaN/Si heterointerfaces was found to be significantly tuned by appropriate thermal annealing. With increasing annealing temperature, the amorphous interlayer formed at the as-bonded interface gradually transforms into a thin crystallized interlayer without any observable defects even after annealing at 1000 °C, while the interlayer stresses at both GaN layer and Si monotonically change due to the interfacial re-crystallization. This work moves an important step forward directly integrating GaN to the present Si CMOS technology with high quality thin interfaces and brings great promises for wafer-scale low-cost fabrication of GaN electronics.

Analysis of interfacial crack initiation mechanism of thermal barrier coatings in isothermal oxidation process based on interfacial stress state

In this paper, the interfacial stress state is used to analyze the interfacial crack initiation mechanism of the thermal barrier coatings (TBCs) during isothermal oxidation. The influence of thermal growth stress, initial residual stress, and creep behavior on the stress distribution is considered to have an accurate simulation result. A parameter that integrates the effects of interfacial normal and tangential stress is modified for evaluating interfacial crack initiation. It is found that, in the cooling stage, the interfacial cracks sprout at the top coat (TC)/thermally grown oxide (TGO) interface valley region and the TGO/bond coat (BC) interface peak region, which agrees with the experimental results. Furthermore, the influence of interfacial roughness on crack initiation is investigated. The result shows that different interfacial roughness affects the sprouting region of interfacial cracks and cracks within the TC layer.

Phase field study on the effect of roughness on interfacial intermetallic compounds of micro-solder joints under multifield coupling

In order to investigate the influence of roughness on the evolution of interfacial intermetallic compounds (IMCs) and stress states at the micro-solder joints under the strongly coupled thermo-mechanical-electric diffusion, the two-dimensional model of the rough interface for the Cu/Sn/Cu sandwich micro-solder joints was established using phase field method. Parameter A as the evaluation parameter of the interface roughness was used to represent the contour arithmetic mean deviation Ra. The evolutions of the average thickness of the interfacial IMCs and stress distribution at the Cu/Sn/Cu micro-solder joints were investigated with the variation of A. The thickness of interfacial IMCs in anode reached its maximum when A was 0, while obtained the minimum when A was 9. In cathode, the average thickness of the interfacial IMCs at A = 0 was thicker than that at A = 1, 3, 5, but thinner than that at A = 7 and 9. In other words, the growth of the interfacial IMCs was inhibited by the interface roughness in anode. While in cathode, the interfacial roughness inhibited the growth of the interfacial IMCs when 0 ≤ A ≤ 5, but promoted the growth of the interfacial IMCs when 7 ≤ A ≤ 9.

Study on Deformation Characteristics and Microstructure Evolution of 2205/AH36 Bimetal Composite in a Novel Hot Forming Process

A new hot forming process of a hot-rolled 2205 duplex stainless/AH36 low-carbon steel bimetal composite (2205/AH36 BC) was proposed in this study, using the Gleeble 3500 thermal-mechanical simulator and hot bending tools. The deformation characteristics of 2205/AH36 BC were studied by hot tensile tests at temperatures from 950 to 1250 °C and strain rates ranging from 0.01 to 1 s−1. The tensile temperature has a great influence on the peak flow stress of the bimetal composite. The main microstructure evolution mechanisms, including dynamic recovery (DRV) and dynamic recrystallization (DRX), changed with the deformation temperatures. The different strain rates and the change of strain rates during the deformation process have an influence on the flow behavior of the bimetal composite. During the hot bending process, qualified parts could be formed successfully without obvious cracks in the interfacial zone. Phase and grain orientation spread (GOS) maps of specimens after hot tensile and forming tests were obtained by the electron backscatter diffraction (EBSD) technique to study the microstructure evolution, respectively. It is found that the effect of the working temperature on microstructure evolution is larger than that of the stacking sequence for 2205/AH36 BC. The considerable geometrically necessary dislocation (GND) accumulation occurs around the interface of 2205/AH36 BC under all imposed working conditions after the hot bending process, due to the interfacial micro-defects and complex stress states.

Interfacial Force-Focusing Effect in Mechanophore-Linked Nanocomposites.

Enhanced force transmission to mechanophores is demonstrated in polymer nanocomposite materials. Spiropyran (SP) mechanophores that change color and fluorescence under mechanical stimuli are functionalized at the interface between SiO2 nanoparticles and polymers. Successful mechanical activation of SP at the interface is confirmed in both solution and solid states. Compared with SP‐linked in bulk polymers, interfacial activation induces greater conversion of SP to its colored merocyanine form and also significantly decreases the activation threshold under tension. Experimental observations are supported by finite element simulation of the interfacial stress state. The interfacial force‐focusing strategy opens a new way to control the reactivity of mechanophores and also potentially indicates interfacial damage in composite materials.

Interfacial Stress Analysis on Skutterudite-based Thermoelectric Joints under Service Conditions

In thermoelectric (TE) devices, the interfacial reliability greatly influenced devices’ durability and power output. For skutterudites (SKD) devices, TE legs and electrodes are bonded together with diffusion barrier layer (DBL). At elevated temperatures, DBL react with SKD matrix or electrode to generate complex interfacial microstructures, which often accompanies evolutions of the thermal, electrical and mechanical properties at the interfaces. In this work, a finite element model containing the interfacial microstructure characteristics based on the experimental results was built to analyze the interfacial stress state in the skutterudite-based TE joints. A single-layer model was applied to screen out the most important parameters of the coefficient of thermal expansion ( CTE ) and the modulus of DBL on the first principle stress. The multilayer model considering the interfacial microstructures evolution was built to quantitively simulate the stress state of the TE joints at different aging temperatures and time. The simulation results show that the reactive CoSb2 layer is the weakest layer in both SKD/Nb and SKD/Zr joints. And by prolonging the aging time, the thickness of the reaction layer continuously increased, leading to a significant raising of the interfacial stress. The tensile testing results of the SKD/Nb joints match the simulation results well, consolidating accuracy and feasibility of this multilayer model. This study provides an important guidance on the design of DBL to improve the TE joints’ mechanical reliability, and a common method to precisely simulate the stress condition in other coating systems.

Simultaneously enhancing the IFSS and monitoring the interfacial stress state of GF/epoxy composites via building in the MWCNT interface sensor

This paper presents an effective technology that could simultaneously enhance the interfacial shear strength (IFSS) and monitor the interfacial stress state between glass fiber and epoxy vinyl ester resin (GF/epoxy). Muiti-walled carbon nanotube (MWCNT) was added to aqueous surfactant solution and dispersed by ultrasonic. Subsequently, MWCNT was deposited on GF surface by physical vapor deposition. The results show that the sensing performance of the developed sensor was dependence on MWCNT solution concentration, interface length, ultrasonic dispersion duration, and immersion cycles. Fiber-bundle pull-out tests show that IFSS of GF/epoxy was enhanced by incorporating MWCNT into the interphase. By measuring resistance change of the MWCNT sensor, the interfacial evolution behaviour was monitored during the pull-out test. The results indicate that the presented technology can be successfully used for in-situ sensing the accumulated interfacial damage and simultaneously enhancing the IFSS of GF/epoxy composites.

Hygroscopic expansion: A key point to describe natural fibre/polymer matrix interface bond strength

The present article aims to investigate the contribution of hygroscopic expansion of flax fibres to interfacial radial stresses and Interfacial Shear Strength (IFSS) of Maleic Anhydride grafted PolyPropylene (MAPP)/Flax biocomposites.During manufacturing of thermoplastic biocomposites and storage at 50% RH, a weight variation is observed, attributed to water content evolution within plant cell-walls. The hygroscopic radial expansion coefficient βr flax of single flax fibres estimated by Environmental Scanning Electron Microscopy (ESEM) observation is many orders of magnitude higher (βf,R = 1.14 ε/Δm) than thermal expansion (αf, R = 78 10−6 ε/°C). Thus, its contribution to the development of residual stresses σrad during processing should be prevalent. A multiscale analysis of interfacial stress state and hygroscopic contribution is performed with the use of a cylindrical concentric model at microscopic scale and asymmetric composite laminates [0, 90°] curvature generation at macroscopic scale. Similar radial stresses are obtained, while relevant values of μ (IFSS/σrad) ≈ 0.46 are calculated. Therefore, the interfacial bond strength of natural fiber/polymer systems should be described by taking into account their hygroscopic behavior.

Micromechanical modeling of damage and load transfer in particulate composites with partially debonded interface

A new micromechanical damage model accounting for progressive interface debonding is developed for composite materials. It consists of an original evolution law of the damage at the interface and an appropriate load transfer law at the matrix-fiber interface integrated into a generalized incremental Mori–Tanaka homogenization scheme. The interface damage evolution is driven by the interfacial stress state while the load transfer is obtained from a new model inspired by the shear lag model. Specifically, such damage evolution is supported by experimental microscopic observations for short glass fiber reinforced polyamide-66.The proposed model is validated based on numerical reference solutions provided from finite element analyses of a representative unit cell of a composite, where imperfect interfaces are represented using cohesive elements. A further comparison with experimental data proves that the proposed model is an alternative to micromechanical models involving weak interfaces in the case of spherical reinforcements. It is shown that the proposed model is able to accurately reproduce the non-linear effective response of composite materials for a broad range of reinforcement shapes, including spherical particles and matrix mechanical properties.

The effect of microscale residual stress from thermal cooldown on the nanoindentation properties of fibre-reinforced composites

A two-step finite element framework is presented that examines the effect of microscale thermal residual stress on the nanoindentation properties of fibre-reinforced composites. Firstly, micromechanical modelling is used to determine the residual stress state following thermal cooldown of a carbon-fibre composite material from cure temperature. A three-dimensional finite element nanoindentation model is then used to characterise the effects of residual stress on material properties determined by nanoindentation theory. The results show that the hardness of the matrix pockets decreases following thermal cooldown due to the existence of equibiaxial tensile residual stresses. The hardness property is also found to decrease for the majority of interfacial region stress states, while the microstructural areas where the effects of the residual stress are nullified are determined. The indentation modulus property is relatively insensitive to the microstructural residual stress, and thus is the recommended indentation property to be determined when carrying out a comparative parametric analysis between microstructural regions. The property changes are shown to be insensitive to any errors associated with contact area estimation using the Oliver and Pharr method.

A new approach to assessing carbon fiber/epoxy interfacial shear strength by tensile test of 45° fiber bundle composites: Experiment, modeling and applicability

This work concentrates on the assessment of carbon fiber/epoxy interfacial shear strength by 45° fiber bundle tensile (45FBT) test. The 45FBT samples for three different carbon fiber/epoxy systems were prepared and tested. The multiscale model based on the generalized methods of cells (GMC) was established to simulate the tensile damage process and analyze the interfacial stress state. The interfacial shear strength in 45FBT specimen was calculated. The 45FBT test was compared with the transverse fiber bundle tensile (TFBT) test. The applicability of the 45FBT test was finally discussed.

Direct restoration modalities of fractured central maxillary incisors: A multi-levels validated finite elements analysis with in vivo strain measurements

ObjectiveTo quantify the influence of fracture geometry and restorative materials rigidity on the stress intensity and distribution of restored fractured central maxillary incisors (CMI) with particular investigation of the adhesive interfaces. Ancillary objectives are to present an innovative technology to measure the in vivo strain state of sound maxillary incisors and to present the collected data. MethodsA validation experimental biomechanics approach has been associated to finite element analysis. FEA models consisted of CMI, periodontal ligament and the corresponding alveolar bone process. Three models were created representing different orientation of the fracture planes. Three different angulations of the fracture plane in buccal–palatal direction were modeled: the fracture plane perpendicular to the long axis in the buccal–palatal direction (0°); the fracture plane inclined bucco-palatally in apical–coronal direction (−30°); the fracture plane inclined palatal-buccally in apical–coronal direction (+30°). First set of computing runs was performed for in vivo FE-model validation purposes. In the second part, a 50N force was applied on the buccal aspect of the CMI models. Ten patients were selected and subjected to the strain measurement of CMI under controlled loading conditions. ResultsThe main differences were noticed in the middle and incisal thirds of incisors crowns, due to the presence of the incisal portion restoration. The stress intensity in −30° models is increased in the enamel structure close to the restoration, due to a thinning of the remaining natural tissues. The rigidity of the restoring material slightly reduces such phenomenon. −30° model exhibits the higher interfacial stress in the adhesive layer with respect to +30° and 0° models. The lower stress intensity was noticed in the 0° models, restoration material rigidity did not influenced the interfacial stress state in 0° models. On the contrary, material rigidity influenced the interfacial stress state in +30° and −30° models, higher rigidity restoring materials exhibits lower interfacial stress with respect to low rigidity materials. SignificanceFracture planes inclined palatal-buccally in apical–coronal direction (+30°) reduce the interfacial stress intensity and natural tissues stress intensity with respect to the other tested configurations.

Influence of peak oral temperatures on veneer–core interface stress state

Objective: There is a growing interest for the use of Y-TZP zirconia as core material in veneered all-ceramic prostheses. The objective of this study was to evaluate the influence of CET on the stress distribution of a porcelain layered to zirconia core single crowns by finite elements analysis.Material and methods: CET of eight different porcelains was considered during the analysis.Results: Results of this study indicated that the mismatch in CET between the veneering porcelain and the Y-TZP zirconia core has to be minimum (0.5–1 μm/mK) so as to decrease the growing of residual stresses which could bring chipping.Conclusions: The stress state due to temperature variation should be carefully taken into consideration while studying the effect of mechanical load on zirconia core crown by FEA. The interfacial stress state can be increased by temperature variation up to 20% with respect to the relative failure parameter (interface strength in this case). This means that stress due to mechanical load combined to temperature variation-induced stress can lead porcelain veneer–zirconia core interfaces to failure.

Casting quality model for casted aluminium silicon carbide based on non-linear thermal expansion

This paper presents the design and development of a model for predicting the casting quality of aluminium silicon carbide based on the first-order shear deformation theory (FSDT) and thermal expansion behaviour. The coefficient of thermal expansion (CTEs) of casted aluminium silicon carbide fibre reinforced material was significantly influenced by the thermal stresses and interfaces between matrix and fibres. The thermal expansion behaviour of the casted aluminium silicon carbide fibre reinforced composite relies on the thermal expansion of the fibres, and influenced by the onset of interfacial strength and residual stress state. The validation shows a good agreement with surface roughness. In order to determine the performance of the model, the analysis of variance (ANOVA) was presented by using SPSS. The performance of casting quality model shows the correlation at the high level of accuracy 99.9% with confidence level of 95% between the experiment and the model.

Thermal Expansion Model for Cast Aluminium Silicon Carbide

This paper presents the development of thermal expansion model for casted aluminium silicon carbide. Thermal expansion in the casting process is one of the most important parameters that influence the casting quality. The thermal expansion model for casted aluminium silicon carbide is developed by the squeeze casting method. A model of numbers evolved for the prediction of the unidirectional fibre and matrix reinforced composites was presented. The coefficient of thermal expansion (CTEs) of aluminium silicon carbide fibres reinforced material was significantly influenced by the thermal stresses and interfaces between matrix and fibres. The thermal expansion behaviour of the casted aluminium silicon carbide fibres reinforced composite relies on the thermal expansion of the fibres, and influenced by the onset of interfacial strength and residual stress state. The validation shows a good agreement among the model and experimental result of LM6 alloys silicon reinforces. As the result, the thermal expansion model for casted aluminium silicon carbide could predict the surface roughness of the casting product.

X-ray diffraction and fracture based analysis of residual stresses in stainless steel–epoxy interfaces with electropolishing and acid etching substrate treatments

The aim of this study is to investigate the effect of a stainless steel surface condition on the thermal residual stresses at a bi-material interface. AISI 304 stainless steel–epoxy specimens with either as-received, nitric acid etched or electropolished substrates were prepared. Exact specimen curvatures and an analytical method were used to estimate residual stresses and the behaviour of the epoxy layer. X-ray diffraction stress measurement (XRD) was performed to determine the interfacial stress state. In addition, a method was developed to examine the interface fracture toughness of the specimens. Based on the results, the residual stress estimation at the interface was confirmed and the effect of the surface treatments on the interface fracture toughness was evaluated.

Evolution of interfacial nanostructures and stress states in Mg matrix composites reinforced with coated continuous carbon fibers

Magnesium (Mg) matrix composites reinforced with 45 vol.% continuous carbon fibers (C f) were fabricated using a pressureless infiltration process in vacuum. In order to modify the interface between the C f and the Mg matrix, the C f were coated with 5.0 mol.% yttria stabilized zirconia (YSZ) in sol–gel route. The C f/Mg composite exhibited a tensile strength of 1.08 GPa which reached 90% of the theoretical prediction by means of the rule of mixture. Microstructural examinations revealed the occurrence of interfacial reaction between the YSZ coating and the Mg matrix, producing a ∼20 nm thick interfacial reaction layer consisting of nanocrystalline particles, which include MgO particles, remaining ZrO 2 particles and a small quantity of ZrC particles. Interfacial reaction could induce a large compressive stress in the interfacial layer. As a result, some nanostructured defects, such as edge dislocations, were formed in interfacial layer due to the compressive stress. In the cooling process of fabricating the composite, the phase transformation of the remaining ZrO 2 from tetragonal to monoclinic could relax the thermal residual stress of interfacial layer.

Interfacial delamination cracking shapes and stress states during wedge indentation in a soft-film-on-hard-substrate system—Computational simulation and experimental studies

Abstract