Interfacial Cohesion Research Articles

Insight into interface cohesion and impurity-induced embrittlement in carbide dispersion strengthen tungsten from first principles

The fundamental understanding of interface properties is crucial in materials design and lifetime predictions. In this work, the stability, adhesion and impurity-induced embrittlement of interfaces between tungsten (W) and transition metal carbides (TMC = ZrC, TiC, TaC, HfC, MoC, and VC) have been investigated by first-principles calculations. For all the systems, the coherent W (100)-TMC(100) interfaces show better stability with lower interface energies than the semi-coherent W (110)-TMC(100) ones. The impurities hydrogen, helium, oxygen, and nitrogen tend to segregate to the coherent interfaces and act as strong embrittlers. Furthermore, the interface could provide a low-barrier channel to facilitate hydrogen and helium transport. The present work provides key mechanistic insights towards interpreting recent experimental studies of the interface structure and the hydrogen isotope retention in W–ZrC, W–TiC, and W–TaC materials under irradiation and guides the preparation of future W-based materials with good resistance to irradiation damage.

Shear resistance of MICP cementing material at the interface between calcareous sand and steel

MICP (Microbially Induced Carbonate Precipitation) technique was firstly adapted to treat the interface between calcareous sand and steel. The influences of cementing material and surface roughness on the interface shear resistance were investigated experimentally. Results show that biomaterial produced by MICP exists mainly in the form of spherical and block crystals, which bonding and coating sand particles. The peak shear resistances of the interface treated by MICP and Gypsum are similar, while the resistance mobilized at 5 mm displacement of interface treated by MICP is the highest. The surface roughness plays a significant role in enhancing the interface cohesion of MICP-treated sample. This work proves that MICP technique is feasible to improve the calcareous sand-steel interface resistance in an environment-friendly way.

Short-range order strengthening in boron-doped high-entropy alloys for cryogenic applications

Boron doping with an adequate concentration is highly desirable for alloy development because it profoundly improves the material's interface cohesion via interfacial segregation. However, scientific and applicable potentials of soluble boron that resides at the alloy internal grains are generally overlooked. Here we report a strategy for overcoming the typically low strengths of face-centered cubic high-entropy alloys (HEAs) through exploiting soluble boron instead of the interfacial boron. We find that soluble boron increases stress/strain field at the recrystallized HEA grain structure, leading to the generation of short-range order (SRO) in those deformation structure under load at 77 K. The highly increased degree of SRO at planar dislocation slip band that forms during straining, proved by electron microscopy and synchrotron X-ray diffraction, strengthens a typical non-equimolar Fe40Mn40Co10Cr10 (at%) HEA, particularly increasing yield strengths by ∼32%, to ∼1.1 GPa compared to those of boron-free reference materials with similar grain sizes. The advent of deformation-induced SRO domains causes severe lattice distortion (specifically, contraction), leading to the increased cryogenic yield strength of ∼210 MPa, but generating micro-voids at grain boundaries. This study on deformation-induced SRO via boron advances the fundamental understanding of SRO impacts on HEA grains and mechanical properties at cryogenic temperatures, which may pave a general pathway for developing a wide range of ultrastrong alloys for cryogenic applications.

Shear properties of the interface between ultra-high performance concrete and normal strength concrete

Many properties of ultra-high performance concrete (UHPC) are superior to those of normal strength concrete (NSC) - including high strength, toughness, and durability, which makes UHPC a promising repair material for damaged NSC structures. The good bonding and shear resistance of the UHPC-NSC interface may enhance the mechanical properties and ensure the impermeability of repaired concrete structures. Eight sets of interface shear push-out tests were conducted in this study. The shear properties of different UHPC-NSC interface treatments, including shallow chiseling, deep chiseling, interfacial adhesives, rebar exposing, grooving, drilling, and post-installed steel studs, were evaluated and discussed. The results demonstrated that the shear strength of the interface was improved by increasing the concrete strength and surface roughness degree. The ranking of the shear strength of interfacial treatments from the highest to the lowest is as follows: post-installed studs, rebar exposing, high roughness (deep chipping), grooving, low roughness (shallow chipping), and holes drilling. In terms of failure modes, the treatments of chipping, the interfacial adhesive, the exposure of rebar, and the drilling of holes demonstrated brittle interface shear failures, whereas the treatments of grooving and post-installed steel studs showed ductile interface shear failures. Finally, a comprehensive method was proposed to calculate the shear strength of the UHPC-NSC interface, taking several effects into account, including the interface cohesion, mechanical interlocking between concrete and rebars, the UHPC grooved joints, and the dowel action of UHPC. The calculated results were in good agreement with the experimental results, indicating that a reliable prediction of the shear strength of the UHPC-NSC interface could be achieved through the proposed model.

When does nanotube grafting on fibers benefit the strength and toughness of composites?

The answer to this question is revealed by our dual scale models, which say that the composite is the strongest and the toughest not when nanotubes themselves absorb energy but when they serve a supporting role in facilitating matrix to do the energy absorption instead. Toughening by means of only nanotube debonding/pull-out is not the most optimal strategy. The model concurrently considers five energy absorbing mechanisms acting at different scales. These mechanisms are nanotube debonding from the matrix, nanotube breakage, nanotube detachment from the (microscopic) fiber, fiber debonding and finally microdamage in the matrix. Our virtual experiments show that the benefit of CNT grafting largely depends on the tensile strength of CNTs and their interfacial cohesion with the matrix. A map of failure modes is constructed in the parametric space of these two CNT properties to help establish a window of properties beneficial for the strength and toughness improvement. The maximal enhancement is obtained when matrix is allowed to absorb energy through micro-scale damage and CNT debonding at the nano-scale has only partial contribution to it. Recommendations for the CNT tensile strength and CNT/matrix interfacial strength, necessary for creation of strong and tough hierarchical composites, are formulated.

Influence of functionalized core-shell structure on the thermodynamic and shape memory properties of nanocomposites.

Filler/matrix interfacial cohesion exerts a straightforward effect on stress transfer at the interface in composite structures, thereby significantly affecting their integrated mechanical properties. Thus, controlling the interface interaction of polymers/fillers is essential for the fabrication of high-performance polymer composites. In this work, a functionalized core-shell structured hybrid was prepared via charge attraction and applied as a novel filler in the trans-1,4-polyisoprene matrix to improve the interfacial interaction of the filler/matrix. A series of tests on the micro- and macroscale was performed to investigate its thermal, mechanical and shape memory performances. The obtained results show that while guaranteeing the shape memory properties of the composites, the utilization of the core-shell structured hybrid not only improved the heat resistant performance, but also contributed to better mechanical properties. This provides solid evidence for the potential of the innovative method presented herein, which may shed some light on the improvement of the interface design strategy and the development of composites with high performances.

Dynamic slant shear bond behavior between new and old concrete

Quasi-static slant shear bond behavior of new-to-old concrete interfaces has been extensively studied. However, the interfaces might be subjected to dynamic loading during their service life. Therefore, this paper presents an experimental investigation to assess dynamic slant shear bond behavior between new and old concrete. The split Hopkinson pressure bar (SHPB) was employed to apply dynamic compressive loads to slant shear specimens. Quasi-static slant shear tests were also conducted for the purpose of comparison. Test results show that the strain rate has significant effects on failure modes, bond strength, absorption energy and interfacial cohesion and friction angles of specimens. The energy absorption capacity of a specimen in the quasi-static test can be regarded as the threshold in the SHPB test, beyond which the specimen is damaged. Failure modes and bond strength of specimens are influenced by the slant angle but not by the surface roughness and the age of interfaces.

Metal-crosslinked ɛ-poly-L-lysine tissue adhesives with high adhesive performance: Inspiration from mussel adhesive environment

Strong glue of mussels has long been considered as an ideal model to design synthetic bio-adhesives but the adhesive strength of metal-crosslinked mussel-inspired glues is not often satisfactory. Herein, inspired by the adhesive environment of mussels, we obtained metal-crosslinked ε-poly-L-lysine adhesives with high adhesive performance by introducing the elements of suitable adhesive environment (SAE) into the adhesives. The elements of SAE were clarified as weak alkaline conditions (pH ∼ 7.4) and low Fe3+ contents. The adhesive strength (∼105 kPa) of the metal-crosslinked adhesives endowed with the elements of SAE (PL-Cat/Fe-SAE) was about 8 times higher than that of fibrin glues. The high adhesive strength was found to originate from distinctive interfacial adhesion and cohesion strength of PL-Cat/Fe-SAE. PL-Cat/Fe-SAE showed strong interfacial adhesion capacity and nearly comparable cohesion strength to those PL-Cat/Fe adhesives with higher Fe3+ contents. The nearly comparable cohesion strength of PL-Cat/Fe-SAE was then found to be due to more amount of stable tris-complex existed in PL-Cat/Fe-SAE. In addition, PL-Cat/Fe-SAE was able to efficiently close the full thickness skin incisions. The study highlighted the importance of introducing SAE elements into the design of tissue adhesives and provided a facile and efficient strategy for constructing tissue adhesives with high adhesive performance.

Probing the local piezoelectric behavior in stretched barium titanate/poly(vinylidene fluoride) nanocomposites

The nanoscale piezoelectric and ferroelectric behavior of barium titanate/poly(vinylidene fluoride) (BT/PVDF) nanocomposite films has been investigated by means of atomic force microscopy (AFM). An uniaxial stretching step was first carried out to promote the polar β crystal phase of the PVDF matrix, as confirmed by infrared spectroscopy and piezoelectric force microscopy (PFM) analysis. Fragmentation of the original polymer crystalline structure upon drawing, as evidenced by the presence of nanometric crystalline blocks did not damage the composite film, thanks to the strong interfacial cohesion between ceramic and polymer brought by nitrodopamine functionalization of the BT inclusions. By scanning the composite surface using PFM, highly piezo-active regions were evidenced and attributed to the BT nanoparticles that could not be identified on the AFM topography images. The precise manipulation of the ferroelectric polarization states in these individual BT grains embedded into the PVDF matrix has been successfully achieved, confirmed by the local electromechanical deformation simultaneously detected. Reversible switching of the out-of-plane polarization orientation spatially confined into the particles was evidenced. The ability of the contact PFM tool to both directly visualize individual piezoelectric nanofillers dispersed into a polymer matrix and monitor the polarization states is demonstrated, thus highlighting the versatility of PFM for the advanced characterization of electroactive nanocomposites.

Interfacial Interaction between Suolunite Crystal and Silica Binding Peptide for Novel Bioinspired Cement.

Cement and concrete have been important construction materials throughout human history. There is an urgent need to explore novel and untraditional cementitious materials to enhance the durability of building materials and structures in response to increased infrastructure demand worldwide. We report an exploratory study on a biocomposite cement based on a large-scale computational study using density functional theory. An explicitly solvated mixture of a mineral calcium silicate hydrate (C-S-H) crystal suolunite (Ca2Si2O5(OH)2·H2O) and a silicon binding peptide with amino acid sequence PRO-PRO-PRO-TRP-LEU-PRO-TYR-MET-PRO-PRO-TRP-SER is constructed using ab initio molecular dynamics (AIMD). Detailed analysis on the interface structure, interatomic bonding, mechanical properties, and solvent effect of this model reveals a complex interplay of different types of covalent and ionic bonding, including ubiquitous hydrogen bonding which plays a crucial role in their properties. The use of the total bond order density (TBOD), a single quantum mechanical metric, for assessing the interfacial cohesion for this composite biocement is proposed. We find that the solvated model has a slightly larger TBOD than the dried one. These results could lead to a systematic search and rational design for different types of bioinspired and hybrid functional materials with other inorganic minerals and organic peptides.

Interfacial characteristics and cohesion mechanisms of linear friction welded dissimilar titanium alloys: Ti–5Al–2Sn–2Zr–4Mo–4Cr (Ti17) and Ti–6Al–2Sn–4Zr–2Mo (Ti6242)

A detailed microstructural examination endeavoring to understand the interfacial phenomena yielding to cohesion in solid-state assembling processes was performed. This study focuses on the transition zone of a dissimilar titanium alloy joint obtained by Linear Friction Welding (LFW) the β-metastable Ti17 to the near-α Ti6242. The transition zone delimitating both alloys is characterized by a sharp microstructure change from acicular HCP (Hexagonal Close-Packed) α′ martensitic laths in the Ti6242 to equiaxed BCC β (Body-Centered Cubic) subgrains in the Ti17; these α′ plates were shown to precipitate within prior-β subgrains remarkably more rotated than the ones formed in the Ti17. Both α′ and β microstructures were found to be intermingled within transitional subgrains demarcating a limited gradient from one chemical composition to the other. These peculiar interfacial grains revealed that the cohesive mechanisms between the rubbing surfaces occurred in the single-phase β domain under severe strain and high-temperature conditions. During the hot deformation process, the mutual migration of the crystalline interfaces from one material to another assisted by a continuous dynamic recrystallization process was identified as the main adhesive mechanism at the junction zone. The latter led to successful cohesion between the rubbing surfaces. Once the reciprocating motion stopped, fast cooling caused both materials to experience either a βlean→α′ or βlean→βmetastable transformation in the interfacial zone depending on their local chemical composition. The limited process time and the subsequent hindered chemical homogenization at the transition zone led to retaining the so-called intermingled α’/βm subgrains constituting the border between both Ti-alloys.

First-principles study of bubble formation and cohesion properties of hydrogen at Fe/W interfaces

First-principles study is used to comparatively investigate the mechanism of bubble formation of hydrogen at Fe/W interfaces and the effects of H on interface cohesion. It is found that hydrogen at interfacial sites has a negative binding energy, which is quite different from W and Fe bulks with interstitial hydrogen. The hydrogen solubility of the interface is bigger than W and Fe bulks with the increasing temperature, predicting that the Fe/W interface can more easily trap hydrogen and rapidly form bubbles. In addition, we also reveal the sites of hydrogen have an important role on cohesion properties of Fe/W interface, and that the obvious increase of interface strength and stability have been found in the locations of hydrogen relatively far away the center between Fe and W interface layers. The derived results are discussed extensively through comparing with available observations in the literature, and could give a deep understanding of hydrogen at Fe/W interfaces.

Strong and Ductile in Situ Titanium Matrix Composites Reinforced by Titanium Boride Whiskers

A facile industrial processing route with low production costs was developed to produce in situ TiBw/Ti matrix composites with a network reinforcement distribution. The formation mechanism, microstructure and mechanical properties are characterized. In contrast to traditional homogeneous TiBw/Ti counterparts with uniform reinforcement distribution, the present material exhibited a comparable ultimate strength, a good fracture toughness of 33.7 ± 0.3 MPa·m1/2, and a significantly elevated tensile ductility increasing by 58% at room temperature. Superior elongation to fracture as large as 67% at 700 °C demonstrated the potential for the follow-up thermo-mechanical processing or forming. Therefore our work may provide inspirations of fabricating cost-effective high-performance metallic structural materials through the tailoring of interfacial cohesion and reinforcement distribution.

Effect of Scanning Speed with UV Laser Cleaning on Adhesive Bonding Tensile Properties of CFRP

The surfaces of the carbon fiber resin matrix reinforced polymer (CFRP) are completely cleaned and partially cleaned by controlling the ultraviolet laser (UV) scanning speed. Residual resin and surface energy of laser cleaning samples are analyzed and correlated to the adhesive bonding tensile properties. The results show that the main damage form of CFRP bonding joints obtained by UV laser complete cleaning and partial cleaning are mixed failure, in which the interface failure and cohesion damage play an important role in the tensile properties of the two kinds of joints, respectively. The surface of the samples after UV laser partial cleaning has been proved to have obvious infrared absorption peaks. Residual resin on the surface of partial cleaning samples is beneficial to improve the tensile properties of bonded samples. The CFRP surface energy by UV laser partial cleaning is 83.35 mJ/m2, which is far higher than that of the original surface. Nevertheless, the CFRP surface energy after UV laser complete cleaning is 56.67 mJ/m2, which is lower than that of UV laser partial cleaning. To a certain extent, the magnitude of the surface energy reflects the bonding property of CFRP. Therefore, the strength of the CFRP adhesive joint after partial cleaning is stronger than that of CFRP joints after complete cleaning.

Adhesives to empower a manipulator inspired by the chameleon tongue

Existing grasping technologies have persistent challenges with unstructured objects and environments, highlighting an increasing demand for methods that conform to various application scenarios. Inspired by the chameleon tongue, a soft-contact grasping manipulator empowered by a class of adhesive gels has been demonstrated. The adhesives enable the manipulator to rapidly and strongly adhere to diverse substrates with varied surfaces, shapes and sizes, also to release objects under mild conditions. The robustness of such adhesive gels was highlighted with the remarkable recyclability, broad temperature tolerance and long-term stability. Furthermore, a general approach was developed to reconcile the contradiction of simultaneously enhancing their interfacial adhesion and cohesion strength that exists in conventional glues. We anticipate that this work will offer a strategy of developing adhesive materials and pave the way towards new applications of soft materials in the emerging fields of soft robotic devices and smart manufacturing.

The construction and verification of toughening model and formula of binary poly(lactic acid)-based TPV with co-continuous structure

Co-continuous morphologies have attracted substantial attention recently as it possesses a significant toughening effect. However, these investigations of toughening poly (lactic acid) (PLA) with co-continuous structure have been limited to simply qualitative explanation. The “reinforced concrete”-like structure is obviously different from the classic “sea-island” structure. Therefore, considering these toughening elements of the rubber content, interfacial cohesion strength and the strength of rubber, and referring to relevant theory models of reinforced concrete, we have established an original theoretical toughening model, at least semi-quantitatively, of the binary PLA-based thermoplastic vulcanizates (TPVs) with co-continuous structure based on PLA/natural rubber (NR) TPVs. Moreover, we reveal that the calibration model is suitable for PLA/nitrile butadiene rubber (NBR) and PLA/epoxidized natural rubber (ENR) systems, with a perfectly Adj. R-Square of 0.97 and 0.94, respectively. It should be mentioned that natural properties of NBR and ENR are significantly distinguished from NR. This study opens up a viable way to quantitatively understand the toughening mechanism with co-continuous structure.

Ab Initio Study of the Combined Effects of Alloying Elements and H on Grain Boundary Cohesion in Ferritic Steels

Hydrogen enhanced decohesion is expected to play a major role in ferritic steels, especially at grain boundaries. Here, we address the effects of some common alloying elements C, V, Cr, and Mn on the H segregation behaviour and the decohesion mechanism at a Σ 5 ( 310 ) [ 001 ] 36.9 ∘ grain boundary in bcc Fe using spin polarized density functional theory calculations. We find that V, Cr, and Mn enhance grain boundary cohesion. Furthermore, all elements have an influence on the segregation energies of the interstitial elements as well as on these elements’ impact on grain boundary cohesion. V slightly promotes segregation of the cohesion enhancing element C. However, none of the elements increase the cohesion enhancing effect of C and reduce the detrimental effect of H on interfacial cohesion at the same time. At an interface which is co-segregated with C, H, and a substitutional element, C and H show only weak interaction, and the highest work of separation is obtained when the substitute is Mn.

Effects of Interface Bonding on the Residual Stresses in Cold-Sprayed Al-6061: A Numerical Investigation

A contact model that accounts for interfacial cohesion and thermal conduction is developed to investigate the influence of bonding on the final residual stresses build-up in cold spray. The residual stress evolution in the cold-sprayed Al-6061 coating on an Al-6061 substrate is investigated via three-dimensional single-particle and multi-particle impact simulations. It is shown that the interface bonding mainly affects the local residual stress distribution near the interfaces. The residual stresses are largely due to the kinetic peening and bonding effects. The thermal cooling has negligible influence. In general, this work finds that peening introduces compressive stress, while bonding causes relaxation. The balance between the peening and the bonding effects, which depends strongly on the local bonding environment, determines the final residual stress in the system. This work suggests that the interface bonding should be considered as one of the essential factors in numerical modeling of the residual stresses evolution in cold spray.

Improvements in Interface Cohesion Evaluation Method for DSM Clustering Analysis

Design Structure Matrix clustering analysis requires reliable evaluation results of interface cohesion among interfacing elements to produce an effective result. However, the existing cohesion evaluation methods such as the Pimmler and Eppinger’s or Sharman’s can provide biased subjective evaluation results depending on the characteristics of the individual evaluator. In this study, we propose a new quantitative evaluation method for the interface cohesion based on the amount of information being exchanged among the interfacing elements. The study shows the comparison results for interface cohesion evaluation between those of the existing methods and the new method to demonstrate the merits of the proposed method.

A practical fracability evaluation for tight sandstone reservoir with natural interface

Hydraulic fracturing has been widely applied to enhance the conductivity in tight sandstone reservoirs, i.e. reservoirs with low porosity and permeability. The interaction between a hydraulic fracture (HF) and a natural fracture (NF), including crossing, arresting and opening (tensile or dilation), are crucial for controlling the fracability of a reservoir. Previous studies have elucidated that shear dilation is the main mechanism for enhancing the permeability of an unconventional reservoir. Moreover, the brittleness index (BI) is considered another critical parameter that controls the fracability of candidates. However, the fracability of candidates with respect to both shear dilation and BI have not been fully investigated. We performed a practical fracability evaluation by integrating the shear dilation mechanism and BI quantification. We obtained the mechanical parameters from mechanical tests conducted on synthetic tight sandstone samples, and we manufactured specimens with different friction coefficients and shear strengths. Next, we performed scaled hydraulic fracturing experiments on 15 identical 10 cm cubic samples using a true tri-axial stress cell, and the interaction mechanisms between HFs and NFs were investigated. We also evaluated the brittleness of each specimen based on a previous BI model and our own novel BI model. We found that a weak interface cohesion with an interaction (between HF and NF) angle of 60° exhibited a shear dilation (or reactivation) mechanism and a higher BI. We thus conclude that such conditions are more favourable for reservoir stimulation (i.e. hydraulic fracturing) in the field.