Adhesion Zone Research Articles

Numerical simulation of single-lap adhesive joint of composite laminates

A universal method is established to research the various possible damage modes of adhesive bond of laminated composites with or without z-pin reinforcements under tensile loads through numerical simulation. A Continuum Damage Mechanic model based on Hashin damage criterion as a user-defined subroutine is developed to simulate the damage of laminates and Z-pins. The Cohesive Zone Model is used to simulate the damage of adhesive damage, interlayer delamination, and Z-pin slipping-out phenomenon. The numerical simulation method is validated for simulating the various damage modes of the usual composite joints through comparing the simulated results and experiments. The research shows that different ply sequences induce different damage modes and ultimate failure loads of composite joints. The ultimate failure load of joint under tension is not affected obviously whether the joints are reinforced with or without z-pins. The reason is that the damage initiation usually locates at the two sides of adhesive zone and z-pins do not react on the reinforcement under tensile load of joint.

Novel development of dynamic behavior of carbon fiber reinforced polymer sandwich panels with stepwise graded adhesive layer

Purpose The purpose of this study is to focus on the developments of carbon fiber reinforced polymer (CFRP) panels with stepwise graded properties on adhesive layer. The various arranges of the graded properties of the adhesive layer have been checked according to experimental results of the literatures and based on applicability. Design/methodology/approach The finite element (FE) models and experimental modal tests of the manufactured CFRP sandwich panel specimens have been investigated. The core thickness, core density and orientation of the fiber direction of the sandwich panel face – sheets have been parametrically checked based on modal behavior. Two fully free and fully clamped boundary conditions (BC) have been checked in stepwise graded adhesive zone (SGAZ) cases and first five non-zero natural frequencies (NF) have been compared. Dynamic response of the SGAZ includes modal analysis and transient dynamic loading have been performed numerically with ABAQUS 6.12 well-known FE code. Findings The first non-zero NF of SGAZ Case 4 was 11.69 per cent higher than homogenous Case 2 and 7.06 per cent lower than Case 1 in fully free boundary conditions. A total of 26.38 per cent is the greatest discrepancy between fist five non-zero NFs of all cases with two BCs (Case 1 vs Case 2 in fully clamped BC). Maximum structural damping behavior and minimum stress picks have been studied during transient dynamic loading analysis of CFRP panel with SGAZ. SGAZ Case 3 (middle adhesive with lower modulus) has increased the maximum structural damping while reducing the minimum out of plain tip displacements during transient dynamic loading by 111.26 per cent in comparison with homogenous Case 2. Also, Case 3 has reduced the Mises stress picks on the adhesive region by 605.68 per cent. Practical implications Making a stepwise graded adhesive region (without any added mass) has been shown that it is a novel and useful way to achieve a wide range of stiffness on CFRP panels. Originality/value Development of the sandwich panels with various stiffness and damping properties.

The influence of binder mobility on the viral entry into a cell

AbstractThe current contribution deals with the simulation of the viral entry into a cell. There are two dominant mechanisms typical of this process: the endocytosis and the fusion with the cellular membrane. However, we only focus on the first scenario. To this end, we consider a virus as a substrate with a constant concentration of receptors on the surface. Opposite to this, the concentration of receptors of the host cell varies and these receptors are free to move over the membrane. When the contact with the cell surface has been achieved, the receptors start to diffuse to the contact (adhesion) zone. The membrane in this zone inflects and forms an envelope around the surface of the virus. This is the way the newly formed vesicle imports its cargo into the cell. In order to simulate the process described, we assume that the differential equation typical of the heat transport is suitable to simulate the diffusion of receptors. We also formulate two boundary conditions: First, we consider the balance of fluxes on the front of the adhesion zone. Here, it is supposed that the velocity is proportional to the gradient of the chemical potential. The second subsidiary condition is the energy balance equation depending on four different contributions: the energy of binding receptors, the free energy of the membrane, the energy due to the curvature of the membrane and the kinetic energy due to the motion of the front. The differential equation itself along with two boundary conditions forms a well‐posed problem which can be solved by applying a direct method, for example the finite difference method. The contribution also includes numerical examples showing the distribution of receptors over the membrane as well as the motion of the front of the adhesion surface. The influence of the mobility of receptors has been studied in particular. (© 2017 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)

The pretarsus of the honeybee

Although the honeybee (Apis mellifera L.) is a well-studied species, the functional morphology of its pretarsal structure is still not fully understood. We conducted an in-depth scanning electron microscopic study on these complex structures to contribute to the comprehension of the pretarsal structure-function relationships. As a result, this study has provided valuable information on the ultrastructure of the pretarsus, and in particular on the spines of the unguitractor surface and the small spines and scalloped surface of the claws with longitudinal grooves. Special attention was given to the adhesive contact zone of the arolium with its highly specialized fibrillary cuticle texture. Remarkably, several of the observed pretarsal structures, such as the pyramidal structures on the unguitractor and the thin hairs on both the grooved claws, and the hairs of the manubrium have not been previously described. All observed structures in this study were characterized with respect to their possible physiological and mechanical roles.

Endoocular OCT assisted epimacular surgery with preliminary vitreoretinal adhesions mapping

SummaryMembranectomy is critical and one difficult stages of macular surgery. The difficulty is caused by heterogeneity of the adhesion of epiretinal tissue to the retina, and if it is large, traumas of the retina appear that are the main cause of loss of visual fields in the central area. Also, that in the overwhelming majority of cases (more than 50%), the onset of membranectomy is accompanied by a trauma of the retina, which occurs when the epiretinal tissue is first captured with forceps. Selective surgery, in which the map of adhesion of epiretinal tissue to the retina is created with the help of OCT at the preoperative stage and membranectomy is carried out only in areas of low adhesion, significantly reduces the probability of traumas of the retina.In the process of vitrectomy and membranectomy, the redistribution of mechanical stress occurs in the epiretinal tissue. Because of this, the topology of the adhesion map changes. Dislocations of the boundaries of high adhesion zones in the process of membranectomy can reach 1.5 mm and with the probability greater than 0.7 are greater than 0.5 mm.Uses endoOCT allows to control these changes in process of surgery, allowing it is essential to increase its efficiency.

Study on impact damage mechanisms and TAI capacity for the composite scarf repair of the primary load-bearing level

As composite material plays a leading role in aircraft, composite bonding repair has been extensively applied. Among composite bonding repairs, the scarf bonding repair is widely adopted and has high repair efficiency especially in primary load-bearing structures. However, the impact damage tolerance and impact damage mechanisms were not considered for repaired structure integrity design yet. This paper experimentally and numerically studied the scarfed bonding repair of the advanced CFRP, which may suffer a low velocity impact load in service. At the central location of adhesive zone, impact energy and response regularity were studied to reveal the competition failure mechanism for inner kinds of materials. In the impact procedure, double force peaks phenomenon and four typical phases were found. Tension after impact (TAI) capacities were also tested to explain the impact damage effects on residual strength. The adhesive damage has strong influence over tension after impact capability. The most easily broken location in the bonded zone is the feathered tip on the back of impact point. The critical impact energy 23J exists for this size of specimen. When the impact energy is higher than the critical 23J, except for the composites damage, the adhesive damage can be observed at the second force dropping. The scarfed adhesive damage occurred at the scarf feathered tip of back side.

The degradation mechanism of Inconel 690TT induced by fretting wear in air

The research of degradation mechanisms of Inconel 690TT during fretting wear in air indicated that degradation mechanisms varied with the fretting regimes. In gross slip regime, the major degradation mechanisms were deformation, oxidation and delamination cracks in the worn subsurface. Delamination cracks in wear debris layer were inclined to nucleate at tribology transformed structure/wear debris layer interface as well as worn surface, accelerating the detachment of material. In partial slip regime, the major degradation mechanisms were deformed asperities at adhesion zone of worn center, oxidation at worn edge and fatigue cracks at the junction of adhesion/oxidation zone in the mode of transgranular and intergranular.

The influence of Y-TZP surface treatment on topography and ceramic/resin cement interfacial fracture toughness

ObjectiveConsider the efficacy of glass infiltration etching (SIE) treatment as a procedure to modify the zirconia surface resulting in higher interfacial fracture toughness. MethodsY-TZP was subjected to 5 different surface treatments conditions consisting of no treatment (G1), SIE followed by hydrofluoric acid treatment (G2), heat treated at 750°C (G3), hydrofluoric acid treated (G4) and airborne-particle abrasion with alumina particles (G5). The effect of surface treatment on roughness was evaluated by Atomic Force Microscopy providing three different parameters: Ra, Rsk and surface area variation. The ceramic/resin cement interface was analyzed by Fracture Mechanics KI test with failure mode determined by fractographic analysis. Weibull’s analysis was also performed to evaluate the structural integrity of the adhesion zone. ResultsG2 and G4 specimens showed very similar, and high Ra values but different surface area variation (33% for G2 and 13% for G4) and they presented the highest fracture toughness (KIC). Weibull’s analysis showed G2 (SIE) tendency to exhibit higher KIC values than the other groups but with more data scatter and a higher early failure probability than G4 specimens. SignificanceSelective glass infiltration etching surface treatment was effective in modifying the zirconia surface roughness, increasing the bonding area and hence the mechanical imbrications at the zirconia/resin cement interface resulting in higher fracture toughness (KIC) values with higher KIC values obtained when failure probability above 20% was expected (Weibull’s distribution) among all the experimental groups.

The method of constructing the diagrams of tangential stresses in the contact zone of an axle wheel with soil

The process of interaction of the driving wheels of mobile energy resources with soil is considered. A computational and experimental method is proposed for plotting the shear stresses in the contact zone of the skid wheel with a supporting surface, based on the use of normal stresses obtained for specific ground conditions. The character of the interaction of the driving wheel of the tractor with various types of supporting base has been studied in detail: a dirt road, stubble, a field prepared for sowing. It is revealed that, contrary to the generally accepted ideas, the slipping wheel has practically no adhesion zone in the contact spot. After touching the tiller of the supporting surface, it immediately begins to shift backward. Therefore, when calculating the shear stresses in the contact spot of the skid wheel with the support, it is more correct to assume that the shift of the elementary points increases as they move away from the entrance to the contact zone and depends on the amount of slippage. When rolling the drive wheel, even with a slight slippage on the deformable surface, there is practically no bonding zone at the point of contact between the two contacting bodies (the tire and the ground). On the surface of the soil, normal stresses reach their maximum, gradually decreasing with increasing depths of its layers. With a slight slipping (up to 10 %), the maximum tangential stresses occur at the back of the contact spot - in the zone of the largest shear deformations of the soil. As the traction load increases, the tangential contact stresses are shifted to the center of the contact patch - to the zone where the deformations of the soil did not exceed the optimum level characteristic for each specific soil type. Thus, the elongation of the tire contact patch is effectively up to a certain level limited by the limiting values of shear deformation of the soil above which the tangential stresses cease to grow and even begin to decline for most types of cohesive soils. It was found that an excessive increase in shear deformation of the soil at slippage leads to a decrease in the efficiency of the wheeled propulsor.

Tough and tunable adhesion of hydrogels: experiments and models

As polymer networks infiltrated with water, hydrogels are major constituents of animal and plant bodies and have diverse engineering applications. While natural hydrogels can robustly adhere to other biological materials, such as bonding of tendons and cartilage on bones and adhesive plaques of mussels, it is challenging to achieve such tough adhesions between synthetic hydrogels and engineering materials. Recent experiments show that chemically anchoring long-chain polymer networks of tough synthetic hydrogels on solid surfaces create adhesions tougher than their natural counterparts, but the underlying mechanism has not been well understood. It is also challenging to tune systematically the adhesion of hydrogels on solids. Here, we provide a quantitative understanding of the mechanism for tough adhesions of hydrogels on solid materials via a combination of experiments, theory, and numerical simulations. Using a coupled cohesive-zone and Mullins-effect model validated by experiments, we reveal the interplays of intrinsic work of adhesion, interfacial strength, and energy dissipation in bulk hydrogels in order to achieve tough adhesions. We further show that hydrogel adhesion can be systematically tuned by tailoring the hydrogel geometry and silanization time of solid substrates, corresponding to the control of energy dissipation zone and intrinsic work of adhesion, respectively. The current work further provides a theoretical foundation for rational design of future biocompatible and underwater adhesives.

Microstructure evolution of Al–Sr master alloy during continuous extrusion

The microstructure evolution of Al–Sr master alloy during continuous extrusion was investigated using X-ray diffractometer, scanning electron microscope and transmission electron microscope. Results indicate that the continuous extrusion process could change the Al4Sr particles of the alloy significantly in size and morphology. The as-cast needle-like Al4Sr particles are broken into small blocks in upsetting zone and crushed heavily in adhesion zone. Plenty of dislocations get tangled up in right-angle bending zone. Al4Sr particles grow in the extending zone. Finally, Al4Sr particles in products are approximately 28 μm in length. Al2Sr particles precipitate during the process. Compared with products by horizontal extrusion, Al4Sr particles by continuous extrusion are finer and distribute more evenly.

Strong adhesion by regulatory T cells induces dendritic cell cytoskeletal polarization and contact-dependent lethargy.

Dendritic cells are targeted by regulatory T (T reg) cells, in a manner that operates as an indirect mode of T cell suppression. In this study, using a combination of single-cell force spectroscopy and structured illumination microscopy, we analyze individual T reg cell-DC interaction events and show that T reg cells exhibit strong intrinsic adhesiveness to DCs. This increased DC adhesion reduces the ability of contacted DCs to engage other antigen-specific cells. We show that this unusually strong LFA-1-dependent adhesiveness of T reg cells is caused in part by their low calpain activities, which normally release integrin-cytoskeleton linkage, and thereby reduce adhesion. Super resolution imaging reveals that such T reg cell adhesion causes sequestration of Fascin-1, an actin-bundling protein essential for immunological synapse formation, and skews Fascin-1-dependent actin polarization in DCs toward the T reg cell adhesion zone. Although it is reversible upon T reg cell disengagement, this sequestration of essential cytoskeletal components causes a lethargic state of DCs, leading to reduced T cell priming. Our results reveal a dynamic cytoskeletal component underlying T reg cell-mediated DC suppression in a contact-dependent manner.

A contact problem for a plane weakened by a periodic system of variable width slots

We consider a problem on compression of an elastic isotropic plane with a periodic system of slots of variable width comparable with elastic deformations. The case of appearance of several contact sections of slot faces contact is studied. Therewith it is considered that on some part of the contact area there arises adhesion of faces, on the remaining part the slippage may happen. The problem on equilibrium of periodical system of slots with partially contacting faces under the action of compressive load is reduced to the problem of linear conjugation of analytic functions. Contact stresses, sizes of contact sections and adhesion zones are determined.

Low-speed bending impact behavior of adhesively bonded single-lap joints

This study addresses the low-speed impact behavior of adhesively bonded single-lap joints. An explicit dynamic finite element analysis was conducted in order to determine the damage initiation and propagation in the adhesive layers of adhesive single-lap joints under a bending impact load. A cohesive zone model was implemented to predict probable failure initiation and propagation along adhesive–adherend interfaces whereas an elasto-plastic material model was used for the adhesive zone between upper and lower adhesive interfaces as well as the adherends. The effect of the plastic deformation ability of adherend material on the damage mechanism of the adhesive layer was also studied for two aluminum materials Al 2024-T3 and Al 5754-0 having different strength and plastic deformation ability. The effects of impact energy (3 and 11 J) and the overlap length (25 and 40 mm) were also investigated. The predicted contact force-time, contact force-central displacement variations, the damage initiation and propagation mechanism were verified with experimental ones. The SEM and macroscope photographs of the adhesive fracture surfaces were similar to those of the explicit dynamic finite element analysis.

Commentary on: Zones of Adhesion of the Abdomen: Implications for Abdominoplasty.

The author of “Zones of Adhesion of the Abdomen: Implications for Abdominoplasty” has used an innovative method to evaluate skin mobility of the anterior and posterior abdomen in patients and cadavers.1 Skin mobility, according to the author, will depend on many factors, such as skin elasticity, subcutaneous tissue thickness, and deep tissue attachment. Although innovative, this method used to evaluate skin mobilization in patients could be improved. The author has used hand traction exerted over the skin to evaluate skin mobility. To use a dynamometer2 attached to a skin staple enables the examiner to obtain similar traction to mobilize each site, which could decrease possible measurement errors. The dynamometer could be tractioned in each direction, and a similar round figure could then be created. Another weak point of the method is the use of headless frozen cadavers. Although the author mentioned that he used fresh cadavers, it is at some point described that the cadavers were frozen. With frozen cadavers, skin mobility is limited, especially considering that only two subjects were used. The use of fresh cadavers would be better; however, even in this case, tissues are not as mobile as they are in live human beings. The idea of moving the abdominal skin is of interest for plastic surgeons. With knowledge of the less mobile areas, selective undermining of these areas could be performed, with more skin advancement and consequently less undermining. A good balance of undermining and traction is paramount to avoid ischemic complications. In the more recently described techniques, such as lipoabdominoplasty, undermining is limited and any localized undermining that could lead to more extensive skin advancement is important. It is also interesting to see how massive weight loss patients present …

Zones of Adhesion of the Abdomen: Implications for Abdominoplasty.

The elucidation of the superficial fascial system (SFS) by Lockwood in 1991 has been the cornerstone of our understanding of abdominal excisional dynamics for the last 25 years. The SFS can be used for closure and, appropriately mobilized, for tension transmission in abdominoplasty, and lower body lifts. The pattern of SFS adhesion to muscle fascia and the zones of adhesion was also described but there are inconsistencies between the description and clinical experience. This study was performed to better describe the pattern of subcutaneous tissue adhesion to the trunk. Twenty pre-abdominoplasty patients were studied. A series of points were marked around the trunk and the skin moved in four opposing directions. The excursions were measured and the median plotted on a diagram. Two fresh cadavers were also dissected, removing all subcutaneous tissue circumferentially from the trunk muscle fascia and marking the strength of the adhesion with a colored pin. Three grades of adhesion were mapped. In the current study, maximal laxity was shown in the mid-lower abdomen and the anterior and lateral chest. Laxity was limited in the anterior and posterior midlines, over the lower back, and the lateral upper thigh. The cadaver dissection mapped adhesion which correlated with the skin laxity diagram. The detailed skin adhesion map better explains features of surface anatomy. Incorporating this understanding a tension vector of abdominoplasty closure obliquely inwards is proposed to maximally harvest the laxity of the anterior and lateral chest and to create further lowering and narrowing of the waist.

Adhesion patterning by a novel air-lock technique enables localization and in-situ real-time imaging of reprogramming events in one-to-one electrofused hybrids.

Although fusion of somatic cells with embryonic stem (ES) cells has been shown to induce reprogramming, single-cell level details of the transitory phenotypic changes that occur during fusion-based reprogramming are still lacking. Our group previously reported on the technique of one-to-one electrofusion via micro-slits in a microfluidic platform. In this study, we focused on developing a novel air-lock patterning technique for creating localized adhesion zones around the micro-slits for cell localization and real-time imaging of post fusion events with a single-cell resolution. Mouse embryonic fibroblasts (MEF) were fused individually with mouse ES cells using a polydimethylsiloxane (PDMS) fusion chip consisting of two feeder channels with a separating wall containing an array of micro-slits (slit width ∼3 μm) at a regular spacing. ES cells and MEFs were introduced separately into the channels, juxtaposed on the micro-slits by dielectrophoresis and fused one-to-one by a pulse voltage. To localize fused cells for on-chip culture and time-lapse microscopy, we implemented a two-step approach of air-lock bovine serum albumin patterning and Matrigel coating to create localized adhesion areas around the micro-slits. As a result of time-lapse imaging, we could determine that cell division occurs within 24 h after fusion, much earlier than the 2–3 days reported by earlier studies. Remarkably, Oct4-GFP (Green Fluorescent Protein) was confirmed after 25 h of fusion and thereafter stably expressed by daughter cells of fused cells. Thus, integrated into our high-yield electrofusion platform, the technique of air-lock assisted adhesion patterning enables a single-cell level tracking of fused cells to highlight cell-level dynamics during fusion-based reprogramming.

Force Bistability in Adhesion Switch

The lateral junctions of epithelial cells must display mechanical stability to form barriers, but also significant plasticity to allow for reorganization during development and repair. In this issue, Biswas et al. (1) extend the use of fluid supported-lipid bilayers (SLBs) to reconstitute function of the key adhesion molecule that initiates lateral junctions of epithelial cells, E-cadherin, and to further study the requirements for mechanical forces in activating the cytoplasmic complex that links E-cadherin to the cytoskeleton (1).

Internal Stresses in PVD Coated Tool Composites

AbstractThe aim of work is the investigation of the internal stresses in PVD coated metal matrix composites (MMC). Sintered MMC substrate is composed of the matrix with the chemical composition corresponding to the high-speed steel, reinforced with the TiC type hard carbide phase. Functionally graded composition of MMC providing of high ductility characteristic of steel in the core zone as well as high hardness characteristic of cemented carbides in the surface zone. Internal stresses were determined with use of finite element method in ANSYS environment. The reason of undertaking the work is necessity of develop the research of internal stresses, occurring in the coating, as well as in the adhesion zone of coating and substrate, which makes it possible to draw valuable conclusions concerning engineering process of the advisable structure and chemical composition of coatings. The investigations were carried out on cutting tool’s models containing defined zones differing in chemical composition.Modelled materials were characteristic of chemical composition corresponding to the high-speed steel at the core, reinforced with the TiC type hard carbide phase with the growing fraction of these phases in the outward direction from the core to the surface, additionally coated with (Ti,Al)N or Ti(C,N) functionally graded PVD coatings.Results of determined internal stresses were compared with the results calculated using experimental X-ray sin2ψ method. It was demonstrated, that the presented model meets the initial criteria, which gives ground to the assumption about its utility for determining the stresses in coatings as well as in functionally graded sintered materials. The results of computer simulations correlate with the experimental results.

Research on torsional friction behavior and fluid load support of PVA/HA composite hydrogel

Hydrogels have been extensively studied for use as synthetic articular cartilage. This study aimed to investigate (1) the torsional friction contact state and the transformation mechanism of PVA/HA composite hydrogel against CoCrMo femoral head and (2) effects of load and torsional angle on torsional friction behavior. The finite element method was used to study fluid load support of PVA/HA composite hydrogel. Results show fluid loss increases gradually of PVA/HA composite hydrogel with torsional friction time, leading to fluid load support decreases. The contact state changes from full slip state to stick–slip mixed state. As the load increases, friction coefficient and adhesion zone increase gradually. As the torsional angle increases, friction coefficient and slip trend of the contact interface increase, resulting in the increase of the slip zone and the reduction of the adhesion zone. Fluid loss increases of PVA/HA composite hydrogel as the load and the torsional angle increase, which causes the decrease of fluid load support and the increase of friction coefficient.