Interface Elements Research Articles

Effect of deposition sequence on interfacial characteristics of Inconel–copper functional bimetallic structures fabricated by directed energy deposition-arc

Interfacial bonding reliability is a critical issue in bimetallic structures. To understand the effect of deposition sequence on interfacial characteristics, bimetallic structures of Inconel and copper alloys were fabricated by directed energy deposition arc (DED-Arc). The interfacial element diffusion behaviors and formation mechanisms were investigated in detail. The bimetallic structure of C18150 on GH4169 exhibits a sound metallurgical bonding interface with a wide interfacial region (∼400 μm), which is attributed to Marangoni convection and intense elemental interdiffusion. The study highlights the feasibility of fabricating large Inconel–copper functional bimetallic structures with sound metallurgical bonding using DED-Arc and it provides a theoretical reference for design and fabrication of bimetallic structures with material-property mismatches.

Immiscible Fe-Mg system diffusion mechanism induced by dynamic recrystallization at the steel/Mg warm rolling interface

Steel/Mg laminate composites were prepared by a warm rolling composite process in this work. The structural characteristics and elemental distribution of the steel/Mg composite interface region were characterized by SEM, EBSD, and TEM. The formation mechanism of interfacial structure and the diffusion mechanism of interfacial elements were analyzed. Finally, the interfacial bonding mechanism of steel/Mg laminate composites was revealed. The results showed that the steel and Mg in the interface region underwent continuous dynamic recrystallization and discontinuous dynamic recrystallization, respectively. This resulted in a gradient distribution of nanoscale steel grains and a uniform distribution of micron-sized Mg grains. There were oxygen-rich bonding region and oxygen-poor bonding region at the steel/Mg warm-rolled composite interface. In the oxygen-poor bonding region, mixing of the immiscible Fe-Mg system occurred, forming an Fe-based supersaturated solid solution. The difference in dynamic recrystallization mechanism leads to the deformation storage energy of the steel being about 24 times that of the Mg. Driven by the difference in deformation energy storage between steel and Mg, Mg atoms diffused to the steel side and resulted in the Fe-based supersaturated solid solution. This study provides a new thought for preparing immiscible metal laminate composites.

A locally modified second-order finite element method for interface problems and its implementation in 2 dimensions

The locally modified finite element method, which is introduced in Frei and Richter [SIAM J. Numer. Anal.52(2014) 2315–2334], is a simple fitted finite element method that is able to resolve weak discontinuities in interface problems. The method is based on a fixed structured coarse mesh, which is then refined into sub-elements to resolve an interior interface. In this work, we extend the locally modified finite element method in two space dimensions to second order using an isoparametric approach in the interface elements. Thereby we need to take care that the resulting curved edges do not lead to degenerate sub-elements. We prove optimala priorierror estimates in theL2-norm and in a discrete energy norm. Finally, we present numerical examples to substantiate the theoretical findings.

Diffusion mechanism of immiscible Fe-Mg system induced by high-density defects at the steel/Mg composite interface

Due to positive mixing heat between Fe and Mg, it is difficult to diffuse for Fe-Mg at the interface of steel/Mg laminated composites, resulting in the inability to achieve high-strength metallurgical bonding. In this paper, 20#steel/Mg laminated composites were prepared by large deformation rolling and subsequent diffusion heat treatment process. The interfacial bonding strength was improved by constructing high-density crystal defects at the interface to promote element diffusion. The mechanisms of interface morphology evolution and element diffusion were analyzed by finite element simulation and theoretical calculation. The results show after diffusion heat treatment, the bond strength of the large deformation rolled interface was increased from 14 MPa to 30 MPa. Fe-Mg transition layer with about 80 nm thickness as well as high-density vacancies, dislocations and grain boundaries were formed in the large deformation rolled interface region. During diffusion heat treatment, Mg elements diffused into grain interior and grain boundary regions of 20#steel under the effect of heat-force coupling, and the thickness of Fe-Mg transition layer increased to 150 nm, forming an Fe-based supersaturated solid solution. The interface with high-density defects constituted a non-equilibrium interface. The 20#steel internal energy in the non-equilibrium interface is able to overcome positive mixing heat of immiscible Fe-Mg system and provide the driving force for Mg elements diffusion. Promoting elemental diffusion by constructing high-density defects can be a new concept to achieve metallurgical bonding at the interface of immiscible metal laminated composites.

Development of Cyclic Interface Shear Test Device and Testing Procedure to Measure the Response of Cohesive Soil-Structure Interface

Abstract Cyclic loading acting on foundations supporting renewable energy systems affects the soil-structure interface properties and shear resistance. The cyclic shear stress and cyclic displacement applied to the cohesive soil-structure interface may cause volume changes and pore pressure build up in the surrounding soil. This article focuses on the development of a new testing device named the cyclic interface shear test (CIST). The CIST is a fully automated device developed to directly measure the response of cohesive soil-structure interface for foundations subjected to long-term cyclic axial loading. This article describes the newly developed testing device, including the design of the shear head and the three-dimensional (3D) printed interface elements, as well as the control system and data acquisition system. Furthermore, the article presents the sample preparation for clayey soil and the recommended testing procedure for conducting static or cyclic interface shear tests, or both. The developed CIST device is capable of applying one-way, two-way, or combined one- and two-way cycles. Furthermore, the CIST is capable of applying different amplitudes, a range of loading frequencies, and a large number of cycles. To demonstrate the capabilities of the CIST device and to finalize the testing procedure, a series of preliminary CISTs and a static baseline test on cohesive soil-3D printed interface were performed.

Numerical aspects of phase field models for low-temperature fracture in asphalt mixtures

Unlike the cohesive interface element model, the phase field model (PFM) is a newly developed computational model which provides a unified approach to predicting crack nucleation, propagation, coalescence and branching without any ad-hoc criterion. Over the years, several variants of the phase field model are presented. This paper aims to investigate the suitability of different phase field models and determine the optimal characteristic functions/model parameters for low-temperature fracture in asphalt mixtures. The analysis results of the phase field method (which belongs to a class of diffuse damage models) are also compared with the interface element model (which belongs to a class of discrete damage models). The models are compared by examining the governing equations and performing numerical simulations on single-edge notch specimens. Furthermore, various aspects of cohesive zone model (CZM) based PFM are discussed including the type of softening laws and damage growth under uniform/non-uniform stress states. It is concluded that brittle phase field models are not fully capable to predict fracture in asphalt mixtures even at low temperatures.

A New Immersed Finite Element Method for Two-Phase Stokes Problems Having Discontinuous Pressure

Abstract In this paper, we develop a new immersed finite element method (IFEM) for two-phase incompressible Stokes flows. We allow the interface to cut the finite elements. On the noninterface element, the standard Crouzeix–Raviart element and the P 0 {P_{0}} element pair is used. On the interface element, the basis functions developed for scalar interface problems (Kwak et al., An analysis of a broken P 1 {P_{1}} -nonconforming finite element method for interface problems, SIAM J. Numer. Anal. (2010)) are modified in such a way that the coupling between the velocity and pressure variable is different. There are two kinds of basis functions. The first kind of basis satisfies the Laplace–Young condition under the assumption of the continuity of the pressure variable. In the second kind, the velocity is of bubble type and is coupled with the discontinuous pressure, still satisfying the Laplace–Young condition. We remark that in the second kind the pressure variable has two degrees of freedom on each interface element. Therefore, our methods can handle the discontinuous pressure case. Numerical results including the case of the discontinuous pressure variable are provided. We see optimal convergence orders for all examples.

Trans-scale elastic–plastic damage analysis of 3D tubular braided composites with void defects

Three-dimensional (3D) tubular braided composites exhibit irreversible plastic deformation and nonlinear behavior due to the void defects and plastic effects of the matrix. Therefore, this paper establishes an elastic–plastic damage constitutive model of 3D tubular braided composites with defects, which is coupled with plastic effects and damage accumulation. Firstly, 3D tubular braided composite models with defects are established by sequential trans-scale analysis method to transfer the mechanical properties of the component materials. Then, according to the brittleness of the fiber or yarn and the plasticity of the matrix, the elastic and elastic–plastic damage model of the fiber and the matrix are established, respectively. On this basis, an interface element is established to characterize the mechanical properties of the interface with the tractor-separation constitutive model. Finally, the finite element results of the axial compression properties of 3D tubular braided composites coupled with the porosity and plasticity of the matrix, the longitudinal shear nonlinearity of the yarn and the bilinear constitutive relationship of the interface are in good agreement with the experimental results.

Microstructure evolution, diffusion behavior, and mechanical properties of a Cu/AlCoCrFeNi2.1 composite under pulsed magnetic field

A Cu/AlCoCrFeNi2.1 composite was fabricated via solid-liquid method. In order to acquire the good interface bonding, the pulsed magnetic field (PMF) treatment was applied during the preparation of the Cu/AlCoCrFeNi2.1 composite. The effects of different processes and parameters, including pulse frequency on the interface microstructure, element distribution, diffusion thickness, and mechanical properties of the composite were investigated. The results demonstrated that PMF treatment effectively decreased the diffusion layer thickness of the composite, and improved mechanical properties of the Cu side. The diffusion thickness of the composite reduced from 31.22 μm to 6.20 μm after applying PMF. The action mechanism of PMF during preparation was revealed. The ultimate tensile strength, yield strength, and elongation of the Cu/AlCoCrFeNi2.1 composite via PMF were 192.6 MPa, 121.7 MPa, and 43.8%, respectively, which were higher than that of the composite without PMF. The maximum shear strengths of the composites with and without PFM were 120.2 MP and 137.4 MPa, respectively. When the pulse frequency was 2 Hz, the macro-segregation was eliminated to form the high-quality interface. This work paves a way for the performance improvement and complex parts preparation of layer composite by using PMF.

Coupled hydromechanical analysis of sparsely fractured crystalline rocks

This paper addresses the issue of evolution and coalescence of localized damage zones in sparsely fractured crystalline rocks. The approach incorporates a constitutive law with embedded discontinuity, which is phrased in terms of both the hydraulic and mechanical response. The formulation takes into account the hydromechanical interaction in regions intercepted by discontinuities. An internal length scale parameter is employed in the definition of equivalent hydraulic conductivity and the tangential stiffness operators, and the onset of newly developed macrocracks is detected by the bifurcation analysis. An enhanced mixed u-p finite element formulation is derived which considers the effect of progressive evolution of the fracture aperture in the weak statements of balance equations. Fully implicit temporal discretization is employed, and the finite element formulation is stabilized by invoking the Polynomial-Pressure-Projection (PPP) technique. A coupled FE analysis is conducted examining the response of Luc du Bonnet granite, with pre-existing fracture network, subjected to plane strain compression that triggers the crack propagation and coalescence. The approach is first verified on some benchmark problems that involve the presence of a dominant fracture. The results of simulations are compared with those obtained using a very fine mesh incorporating interface elements. Later, a series of coupled analyses are carried out examining the hydromechanical response in the presence of multiple fractures.

A numerical model for basic creep of concrete with aging and damage on beams

This work presents a methodology to model the basic creep of concrete, considering aging and damage. Continuum elements with viscoelastic material represent the basic creep with aging using the solidification theory; interface elements with a cohesive zone model describe damage behavior through a linear softening law. Given the challenges of obtaining a unique set of parameters from experimental tests, a calibration process based on decoupling the physical phenomena is adopted. In addition, an inverse analysis is used when characterization tests are not available, allowing an indirect model calibration. Afterward, numerical results are compared with experimental data from bending creep tests. These results show that the proposed methodology can accurately represent concrete creep behavior at different load levels and specimen sizes besides predicting the beams’ residual capacity observed in tests with high load levels.

Effects of Simulation Games on students’ Computational Thinking and Game Experience for Programming Courses in Primary School

There is substantial evidence that incorporating interactive environments for game-based instruction has a significant potential to support the development of computational thinking and programming skills in primary education students. However, it is not clear whether a simulation game (SG) with different user interface elements, created via three-dimensional (3D) virtual worlds and visual programming environments to project various problem-solving exercises in a simulated reality, can significantly influence students to think and practice "computationally" their solution plans into code. The current study aims to identify any possible added value of each instructional approach by measuring students’ game experience and learning performance. This quasi-experimental study involved ninety participants (n = 90) aged between 10 and 11 years that consisted of two comparison conditions. The experimental group (n = 45) received training using OpenSimulator in combination with Scratch4SL, whereas the control group (n = 45) was trained using Scratch. The findings indicate considerable differences in students’ game experience and satisfaction, but no statistically significant difference in their learning performance and knowledge gain was identified. This study provides several design implications for user interface and game elements to inform educational practitioners and instructors about the benefits that each approach can offer students for better knowledge acquisition and deeper disciplinary understanding.

NONLINEAR LATERAL RESPONSE OF PILE GROUP IN CLAY USING THE MODIFIED CAM CLAY SOIL MODEL

Lateral pile response of the 3 × 3 square pile group has been investigated in terms of lateral displacement and maximum bending moment using three-dimensional finite element analysis. Soil is represented using 8-node isoparametric elements. Piles and pile cap are modelled using 20-node isoparametric elements. The 16-node isoparametric interface elements are used to establish the continuity between the pile and surrounding soil. Soil is represented by the modified Cam clay criterion. The entire code has been developed in FORTRAN 90. The parametric study has been performed to investigate the effect of yield criteria, soil modulus, pile spacing, pile diameter and pile length-to-diameter ratio on the response of the 3 × 3 pile group embedded in clay. A considerable effect of these parameters is observed. It is found that the maximum bending moment in the middle row of the pile group is higher than the front and rear rows for all cases considered in the study. The pile displacement and bending moments in the pile group reduce with an increase in soil modulus, pile spacing and pile diameter. As pile slenderness is increased, it causes an increase in displacement of the pile and a decrease in the maximum bending moment. The modified Cam clay model predicts greater displacements as compared to the Mohr-Coulomb model highlighting the impact of p0 on the yield surface. From the results obtained, the ultimate loads are predicted at a displacement of 5 mm, 10 % of diameter and 20% of diameter.

Sensitivity modelling with objective damage assessment of unreinforced masonry façades undergoing different subsidence settlement patterns

This study aims to investigate the damage response of unreinforced masonry (URM) façades resting on strip foundations and subjected to ground settlements via numerical models. The models depict the non-linear constitutive behaviour of both the masonry, via smeared cracking, and of the soil-foundation interaction, via nonlinear interface elements. The influence of building features, such as the masonry material, the length over height (L/H) ratio of the geometry, the wall thickness, the number and size of openings and different types of strip foundations (i.e. reinforced concrete and unreinforced) is examined. A sensitivity study additionally investigates the influence of the interface stiffness and its constitutive model. A Gaussian curve is used to replicate the shape of the ground settlements; These simulate the loss of support underneath the foundation due to urban subsidence. Eight settlement shapes are applied in the FE models, including both symmetric and asymmetric profiles, while the angular distortion is used to measure their intensity. A new aspect is that the extent of the induced damage to the façade is assessed objectively using a damage parameter that represents the number, length and width of cracks in a single scalar value. The method distinguishes between the applied settlement profile at the bottom of the interface and the retrieved settlement profile measured on the façade. The analyses indicate that for a value of the angular distortion equal to 2 ‰ (or 1/500), computed from the resulting deformations of the façades, 60% of the models exhibit serviceability damage associated with cracks of about 5 mm width. Accordingly, the limit values available in the literature are observed to be too optimistic and not conservative in relation to the analyses presented in this study. A key outcome is that facades with an L/H smaller or equal to 1 do not exhibit cracks wider than 1 mm. Façades on reinforced concrete foundations were observed to be less susceptible to settlement damage, compared to unreinforced ones.

Damage propagation analysis of CFRP laminate by quasi-3D XFEM using hexahedral elements

A quasi-three-dimensional extend finite element method (XFEM) is applied to damage propagation analyses of carbon fiber reinforced plastics (CFRPs) laminate. An eight-node quadrilateral interface element and an eight-node hexahedral continuum element enriched with only the Heaviside function are used to model delamination and matrix cracks, respectively. Zig-zag enhanced cohesive zone model or the zig-zag cohesive zone model is introduced to a delamination and a matrix crack. The implicit static method is then used to solve system equations considering material nonlinearity. The Weibull damage criterion is used to predict fiber breakage when necessary. The results of damage propagation analyses were compared with experimental results obtained using open-hole tension tests, quasi-static indentation tests, and compression-after-impact tests. It was shown that the quasi-three-dimensional XFEM is an effective method for damage propagation analysis of CFRP laminates.

New Ways for Patients to Make Sense of Their Electronic Health Record Data Using the Discovery Web Application: Think-Aloud Evaluation Study.

In the United States, patients can access their electronic health record (EHR) data through patient portals. However, current patient portals are mainly focused on a single provider, with very limited data sharing capabilities and put low emphasis on independent sensemaking of the EHR data. This makes it very challenging for patients to switch between different portals and aggregate the data to obtain a complete picture of their medical history and to make sense of it. Owing to this fragmentation, patients are exposed to numerous inconveniences such as medical errors, repeated tests, and limited self-advocacy. To overcome the limitations of EHR patient portals, we designed and developed Discovery-a web-based application that aggregates EHR data from multiple providers and present them to the patient for efficient exploration and sensemaking. To learn how well Discovery meets the patients' sensemaking needs and what features should such applications include, we conducted an evaluation study. We conducted a remote study with 14 participants. In a 60-minute session and relying on the think-aloud protocol, participants were asked to complete a variety of sensemaking tasks and provide feedback upon completion. The audio materials were transcribed for analysis and the video recordings of the users' interactions with Discovery were annotated to provide additional context. These combined textual data were thematically analyzed to surface themes that reflect how participants used Discovery's features, what sensemaking of their EHR data really entails, and what features are desirable to support that process better. We found that Discovery provided much needed features and could be used in a variety of everyday scenarios, especially for preparing and during clinical visits and also for raising awareness, reflection, and planning. According to the study participants, Discovery provided a robust set of features for supporting independent exploration and sensemaking of their EHR data: summary and quick overview of the data, finding prevalence, periodicity, co-occurrence, and pre-post of medical events, as well as comparing medical record types and subtypes across providers. In addition, we extracted important design implications from the user feedback on data exploration with multiple views and nonstandard user interface elements. Patient-centered sensemaking tools should have a core set of features that can be learned quickly and support common use cases for a variety of users. The patients should be able to detect time-oriented patterns of medical events and get enough context and explanation on demand in a single exploration view that feels warm and familiar and relies on patient-friendly language. However, this view should have enough plasticity to adjust to the patient's information needs as the sensemaking unfolds. Future designs should include the physicians in the patient's sensemaking process and improve the communication in clinical visits and via messaging.

A validation study of a fixed‐based, medium fidelity driving simulator for human–machine interfaces visual distraction testing

AbstractStudies comparing results captured in a simulator with those on road are important to validate the approach but are scarce in the context of secondary task distraction due to the potential ramifications of diverting attention away from safe driving. The authors compare distraction‐related data from two studies exploring human–machine interfaces (HMI) design: one conducted in a static, medium‐fidelity driving simulator with a vehicle enclosure and immersive visual environment, and one conducted on road. In both, 19 drivers undertook an identical selection of touchscreen, point‐and‐select tasks. The magnitude of visual distraction (defined as off‐road glances directed towards the touchscreen) differed between the road and the simulator, with drivers making more and longer off‐road glances when interacting with the interface on road. However, the ordering of effects in response to changes to the complexity of interface design was the same. For example, the number and duration of off‐road glances increased with increasing number of interface elements, and smaller targets attracted longer off‐road glances, in both the road and simulator studies. The work demonstrates good relative validity for the use of medium‐fidelity driving simulators for HMI‐visual distraction testing, supporting their application in this context, and adds to the literature regarding the visual demand characteristics of in‐vehicle interfaces.

Preparation, Microstructure, and Interface Quality of Cr3C2-NiCr Cladding Layer on the Surface of Q235 Steel

In this study, a Cr3C2-NiCr cermet cladding layer was prepared on the surface of Q235 steel via a high-speed laser cladding method. The effects of laser power, scanning speed, and overlap rate on the microstructure, cladding quality, and interfacial elements diffusion of Cr3C2-NiCr/Q235 steel were studied. The results show that there was an obvious transition layer at the interface of the Cr3C2-NiCr cladding layer and Q235 steel, indicating that the Cr3C2-NiCr cladding layer had an adequate metallurgical bond with the matrix. Fe, Cr, and Ni were diffused distinctly between the cladding layer and the matrix. The height and width of the Cr3C2-NiCr cladding layer increased, while the dilution rate decreased with the increase in the laser power. The maximum thickness of the transition layer was about 50 μm for the 6 mm/s sample, the weld heat affected zone was smaller, and it was shown that the productivity can be effectively improved. The sample with a 40% overlap rate exhibited the best flatness. The optimal laser power, scanning speed, and overlap rate of the Cr3C2-NiCr/Q235 steel were 1500 W, 6 mm/s, and 40%, respectively.

Quasi in-situ observation of Ni-plated solder from various fracture mechanism using EBSD

In this study, Electron Backscattered Diffraction (EBSD) was used to investigate the blocking effect of novel electroplated Ni in order to inhibit the growth of IMC layers in high density packaging technology. The diffusion of interfacial elements was analyzed as the main cause for compound growth after high temperature storage. The grain orientation tends to be consistent and the grain size increased with increasing time. And the blocking effect of Ni was calculated from the atomic diffusion level. Moreover, the mechanical properties showed an increasing and then decreasing change with time. In nanopush ball experiments, we observed three fracture modes. The fracture type shifted from Type I to Type II to Type III due to the increase of IMC thickness and the generation of Cu6Sn5.

Study on Deformation Characteristics of Surrounding Rock of Roadway with Coal–Rock Interface

Surrounding rock of roadway with a coal–rock interface is a common form in coal mines. In order to determine deformation characteristics and obtain the control principle of roadways with a coal–rock interface, the interface between the roof and coal seam was added to simulate the weak cohesion between the stratum. In this model, the interface shear stiffness was considered to be one of the key factors affecting horizontal inward movement of the roadway sidewalls. The deformation of the roadway with or without coal–rock interface under different burial depths was analyzed. Then, the shear stiffness of the interface element was changed to study the influence of shear stiffness on roadway deformation. At the same time, the characteristics of discontinuous deformation caused by the coal–rock interface at different positions in the roadway were studied. The results show that the roadway sidewall appeared to bulge in the middle and there is no dislocation and a small deformation in the contact position of the roadway sidewall with the roof and the floor when there is no interface between the stratum of the roadway. When there is an interface, the sidewall of the roadway is extruded as a whole, the slip and dislocation between the coal sidewall and the roof were obvious, and the maximum deformation of the sidewall is 1.68 times that of the roadway without an interface. When the shear stiffness of the interface is low, the deformation and the range of the plastic zone of roadway are large, with a large deformation at the upper part of the roadway sidewall, and a small deformation at the lower part of the roadway sidewall. The deformation of sidewall at the interface position decreases gradually with the increase of the interface shear stiffness, approaching the shape without the interface. When the coal–rock interface is at the sidewall of the roadway, the deformation of the rock and coal body at the interface is discontinuous, with slip and dislocation. The greater the proportion of rock height in the roadway sidewall, the greater the rock deformation. On the contrary, the coal deformation increases. It is more reasonable to simulate the deformation of roadways by adding a coal–rock interface, and the results are closer to the actual situation.