Adhesion Zone Research Articles

Adhesive joints for composite materials produced by additive manufacturing

Composite materials are joined in many occasions with adhesive joints due to the condition of the materials, the ease of repair, the loading conditions, the affectation by corrosion and chemical attacks. However, the efficiency of these bonding schemes is related to multiple factors, among them, the length and the width of the adhesion zone and the thickness of the adhesive. In this work, we analyze the factors associated with the surface contact of the substrates. We define a numerical model using the finite element method and study the parameters related to the physical condition, considering optimal results based on the data of the strength provided by the suppliers of adhesives.

Resistance element weld-bonding and resistance spot weld-bonding of Mg alloy/austenitic stainless steel

Mg alloy/austenitic stainless steel (ASS) joints were produced by resistance element weld-bonding (REWB) and resistance spot weld-bonding (RSWB) techniques. Both joints consisted of two zones, namely, the adhesive zone and weld zone. The weld zone of the REWB joints was formed through a metallurgical reaction between the rivet and ASS. The microstructure of the fusion zone consisted of austenite and intercrystalline delta ferrite. The weld zone of the RSWB joints was formed via welding-brazing mechanism (involving molten Mg alloy and solid ASS), and the nugget was formed in the Mg alloy. The nugget microstructure consisted of fine columnar dendritic structure. Digital image correlation (DIC) analysis was used to study the deformation behavior and strain evolution in the loading direction during lap-shear test. The REWB and RSWB joints experienced lower degree of out-of-plane displacement, sustained higher peak load, and exhibited higher strain to failure than their conventional counterparts. However, the REWB joints exhibited superior lap-shear performance, with high energy absorption and favorable failure mode (pull out failure in the ASS sheet). Upon the failure of the adhesive zone at peak load, the load was sustained by the weld, and the final failure occurred via pullout mode in the ASS. The RSWB joints failed in a sudden manner, mainly by cohesive failure in the adhesive zone and Mg alloy nugget/ASS interface failure in the weld zone.

Contact of faces of a rectilinear crack under complex loading and various contact conditions

The problem of partial contact of faces of a rectilinear crack in a uniform elastic plane under given tensile and shear stresses at infinity as well as two compressive concentrated forces applied near the crack is investigated. Three variants of problem statement are considered: smooth contact, sliding contact, and contact with slip and adhesion between the faces of the crack. Using Kolosov–Muskhelishvili complex potentials, the problem is reduced to a conjugation problem, and a solution of the last one is obtained in analytic form. Transcendental equations to determine the boundaries of contact area and adhesion zone are derived. Conditions are found for cases when the contact area of crack faces degenerates into a point or takes an entire crack. It is shown that an adhesion zone disappears and a mutual slip of crack faces occurs along an entire contact area, if a ratio of tangential and normal stresses given at infinity is larger than a certain value. The results of calculation of boundaries of contact area and adhesion zone, stress intensity factors, and distributions of normal and tangential contact stresses are presented.

Modern optimizing techniques of surgical treatment of proliferative diabetic retinopathy

Aim. To evaluate the clinical efficacy of microinvasive vitrectomy and three-dimensional digital imaging in patients with proliferative diabetic retinopathy.
 Methods. The clinical treatment results were studied in 62 patients (62 eyes) with proliferative diabetic retinopathy complicated by tractional retinal detachment who underwent vitreoretinal surgery with the use of microinvasive techniques and three-dimensional digital imaging. There were 38 (61%) women, 24 (39%) men, mean age 57±5.2 years. The duration of diabetes mellitus was 6 to 13 years (an average of 11.7 years). Of the 62 patients, 11 had insulin-dependent diabetes mellitus, and 51 had non-insulin-dependent diabetes.
 Results. Final anatomical result (the elimination of the zones of proliferation and adhesion of the retina) was reached in 59/62 (95.1%) of the eyes: in 54/62 (87%) eyes after the first intervention, in 8/62 eyes after additional surgical intervention. The maximum corrected visual acuity increased in 55/62 (88.7%) eyes from 0.01±0.12 to 0.22±0.11 (p <0.05); in 3/62 (4.8%) eyes remained the same; 4/62 (6.5%) eyes had visual impairment. Complications were diagnosed in 14 (22.6%) of the eyes: retinal tears (10), hemophthalmus (2), subchoroid hemorrhage (1), detachment of the choroid (1). Postoperative control of intraocular pressure demonstrated the following: 36 (58.1%) eyes had normal intraocular pressure (11–22 mm Hg), 20 (32.3%) — increased intraocular pressure (≥22 mm Hg), 6 (9.7%) — reduced intraocular pressure (≤10 mm Hg). In the postoperative period (up to 1 month after surgery) additional surgical interventions were performed on 8/62 (12.9%) eyes.
 Conclusion. In patients with proliferative diabetic retinopathy, the use of microinvasive vitreoretinal technologies and digital imaging system provide high anatomical (95.1% of patients) and functional results (88.7% of patients).

Registry Kinetics of Myosin Motor Stacks Driven by Mechanical Force-Induced Actin Turnover

Actin filaments associated with myosin motors constitute the cytoskeletal force-generating machinery for many types of adherent cells. These actomyosin units are structurally ordered in muscle cells and, in particular, may be spatially registered across neighboring actin bundles. Such registry or stacking of myosin filaments have been recently observed in ordered actin bundles of even fibroblasts with super-resolution microscopy techniques. We introduce here a model for the dynamics of stacking arising from long-range mechanical interactions between actomyosin units through mutual contractile deformations of the intervening cytoskeletal network. The dynamics of registry involve two key processes: 1) polymerization and depolymerization of actin filaments and 2) remodeling of cross-linker-rich actin adhesion zones, both of which are, in principle, mechanosensitive. By calculating the elastic forces that drive registry and their effect on actin polymerization rates, we estimate a characteristic timescale of tens of minutes for registry to be established, in agreement with experimentally observed timescales for individual kinetic processes involved in myosin stack formation, which we track and quantify. This model elucidates the role of actin turnover dynamics in myosin stacking and explains the loss of stacks seen when actin assembly or disassembly and cross-linking is experimentally disrupted in fibroblasts.

Partial closure of the periodic system of variable width bridged slits in an isotropic medium under compression

The problem of compression of an isotropic medium by a periodic system of variable width slits comparable with elastic deformations is considered. The slit faces are under internal pressure. It is considered that the slits have end zones wherein material's tractions act. It is accepted that interaction of the slit's surface under applied loads may reduce the formation of contact zones of their surfaces. The formation of several contact areas of faces of each slit is studied. Therewith, it is considered that on some parts of a contact area there happens stick of the faces, on the remaining part there may happen slippage. The problem of equilibrium of a periodic system of slits with partially contacting faces under compressing load is reduced to the problem of linear conjugation of analytic functions. Determination of unknown parameters characterizing partial closing of a periodic system of variable width slits is reduced to the solution of the system of singular integro-differential equations. The contact stresses, the tractions in bonds between the slit faces in the end zones, the sizes of the contact areas, the adhesion and end zones are studied.

Contact Problem for a Rigid Punch and an Elastic Half Space as an Inverse Problem

We solve a contact problem of indentation of a punch into an elastic half space with regard for the friction and in the presence of the zones of adhesion, sliding, and separation. The applied approach is based on the statement of the problem in the form of the inverse problem in which the Coulomb law of friction is used as an additional condition in the regions with friction. In the formulation of the inverse problem, we take into account the presence of the zones of adhesion whose sizes are unknown. The correctness of the solution of the inverse problem is analyzed. The proposed approach, in combination with the procedure of discretization, enables us to determine the zones of microsliding alternating with the zones of adhesion and separation.

Effects of orbital septum fat redistribution on multiple malformation of upper eyelid after blepharoplasty

Objective The multiple malformation of upper eyelid, including the excessive width of fold line, sunken and/or multiple folded upper eyelid are the common complications after blepharoplasty. The aim of this study was to investigate the clinical effect of orbital septum fat redistribution on correcting these deformities. Methods From September 2015 to September 2017, 38 patients with multiple malformations of upper eyelid were treated. The incision of upper eyelid and the excessive skin was designed and resected. After completely relieving the scar adhesion zones, we set the lateral orbital septum fat free and transposed it to the inner side of orbital septum or superior border of tarsus with suturing fixation. Then we routinely completed the double eyelid operation. Results Thirty-eight patients with multiple malformations of upper eyelid were treated successfully. The patients were followed up for 6 months to one year, and the results were totally satisfactory. The operation was not performed again. Conclusions The orbital septum fat redistribution can successfully correct the multiple malformation of upper eyelid. It should become a regular procedure in blepharoplasty. Key words: Double eyelid reconstruction; Sunken upper eyelid; Excessive width of fold line; Multiple folded upper eyelids; Orbital septal fat replacement

Experimental and numerical investigation of the high-velocity impact resistance of fiber metal laminates and Al 6061-T6 by using electromagnetic launcher

Fiber metal laminates (FMLs) are composites that have better mechanical properties (e.g. specific stiffness, strength, and impact resistance) than metallic materials. FMLs can be use in automobile and aviation industries as performance-enhancing or weight-lightening materials. To use FMLs in industries, a numerical analysis process should be established to reduce experimental cost and time. To establish such a process, the properties of adhesive zone materials in FMLs at delamination conditions should be determined. In this study, FMLs were produced, and the properties of the adhesive zone materials were determined from the strain energy release rate. Based on these properties, numerical analysis was performed through LS-DYNA for metallic Al 6061-T6 and by ABAQUS for FMLs. The Johnson-Cook strength and damage model, which can represent the strain rate effect, were used as the material model. The adhesive film was expressed by strain energy release rate, and self-reinforce polypropylene had FLD without cohesive zone model (CZM). Furthermore, the impact resistances of FMLs and Al 6061-T6 were investigated and compared at high velocities by developing an electromagnetic launcher. The impact resistance of the FMLs was investigated using impact test and numerical analysis, showed that FMLs had better impact resistance than metallic materials at high velocities. This numerical analysis also provided an impact prediction method at highvelocity impact phenomenon without CZM.

The Effect of Platelet-Rich Plasma on Morphogenesis and Expression of Chondrogenic Marker Genes by Chondrocyte-Like Cells of the Rat Nucleus Pulposus in Vitro

The aim of the study was to investigate the effect of 3, 10, and 20% of platelet-rich rat plasma (PRP) on the morphological characteristics of chondrocyte-like cells of the rat nucleus pulposus (NP) and the expression of chondrogenic genes ACAN, COLII, GPC3, MGP, PTN, ANXA3, and VIM in vitro. A dose-dependent increase of NP cell viability was observed in cultures supplemented with 3, 10, and 20% PRP. Platelets showed tropicity to blast-like cells in culture and formed adhesion zones. Differentiation of blast-like cells was observed and dividing cells were identified on day 14 of cultivation with 20% PRP. PRP prevented the decrease of chondrogenic gene expression in a dose-dependent manner, with 20% PRP being the most efficient. Expression of the majority of chondrogenic genes studied was observed in these cultures: the expression of COLII increased 2.9 times (P = 0.002); that of VIM, 2.1 times (P = 0.0003); that of ANXA3, 2.3 times (P = 0.0003); that of GPC3, 1.4 times (P = 0.0011); that of PTN, 1.6 times (P = 0.0017); and that of ACAN, 1.2 times (P = 0.0606).

Durability of composite assemblies under extreme conditions: Thermomechanical damage prediction of a double-lap bonded composite assembly subject to impact and high temperature

The objective of this study is to simulate and predict the thermomechanical damage of composite material assemblies subjected to impact load while in a high temperature environment. Three-dimensional models were developed for a glass-fiber reinforced vinyl ester double-lap bonded composite assembly subject to combined mechanical and high thermal loads. Both thermal and mechanical models were implemented in the finite element analysis software Abaqus, using sequential heat transfer and dynamic implicit simulations. The thermal model is customized to properly simulate the thermal behavior of composites and generate accurate results while the mechanical model uses the existing functions of Abaqus. For a double-lap composite assembly, thermomechanical failure is predicted in the adhesive zone, at the adherent/adhesive interface, as the adhesive deteriorates at the early stages of exposure. The adherent also deteriorates but at a slower rate. Furthermore, stress concentration is observed at the edges of the stress distribution along the adhesive length, while the average stress along the length decreases gradually as a function of the fire exposure time. The conducted simulations made it possible to predict the stress distribution field variation as a function of time in the double-lap bonded assembly under a combined thermal-impact load. This would serve as a valuable tool for composite structure designers in sizing bonded composite assemblies for their structural projects, as the specifications for certain structures impose a time of evacuation of the structure during a shock and triggering of a fire.

Contact Problem of a Periodic System of Variable Width Slits with Partially Interacting Edges in the Presence of End Zones of Plastic Deformation

A problem of compression of an isotropic medium with a periodic system of variable width slits compared with elastic displacements is under consideration. The edges of the slits are under the action of internal pressure. It is assumed that the ends of the slits have zones of plastic deformation. The presence of several zones of contact of the edges of each slit is studied in the assumption that one of the section may have slippage. The problem of equilibrium of the periodic system of slits with partially contacting edges under the action of a compressive load reduces to the problem of linear coupling of analytical functions. Contact stresses and the sizes of contact zones, adhesion zones, and end zones of plastic deformations are determined.

Higher order Hermite enriched contact finite elements for adhesive contact problems

It is known that during the simulation of the adhesive contact problems highly nonlinear responses of interaction forces occur within the very narrow adhesive zone. It leads to the loss of quadratic-rate of convergence during Newton-Raphson iterations and unstable computational behaviour. In case of standard finite element formulation, a very fine mesh resolution is needed for the stable computations, but a significant computational cost is associated. For minimising the cost without the loss of accuracy of the solution, contact surface enrichment approaches have been presented. These approaches utilise the higher-order Lagrangian polynomial functions for the enrichment of contact finite elements. In the present work, based on the incorporation of fifth- and seventh-order Hermite interpolation functions two new enriched contact finite elements are formulated. The performance of proposed enriched contact finite elements is demonstrated through the simulation of peeling of an initially flat deformable strip from a rigid substrate. A stable solution is obtained at a relatively coarser mesh than the fully Lagrangian discretised finite element mesh. It is shown that the proposed higher order Hermite enriched contact finite elements attain better performance when compared with earlier introduced enriched elements.

Restoration of cellular integrity following “ballistic” pronuclear exchange during Tetrahymena conjugation

During sexual reproduction or conjugation, ciliates form a specialized cell adhesion zone for the purpose of exchanging gametic pronuclei. Hundreds of individual membrane fusion events transform the adhesion zone into a perforated membrane curtain, the mating junction. Pronuclei from each mating partner are propelled through this fenestrated membrane junction by a web of short, cris-crossing microtubules. Pronuclear passage results in the formation of two breaches in the membrane junction. Following pronuclear exchange and karyogamy (fertilization), cells seal these twin membrane breaches thereby re-establishing cellular independence. This would seem like a straightforward problem: simply grow membrane in from the edges of each breach in a fashion similar to how animal cells “grow” their cytokinetic furrows or how plant cells construct a cell wall during mitosis. Serial section electron microscopy and 3-D electron tomography reveal that the actual mechanism is less straightforward. Each of the two membrane breaches transforms into a bowed membrane assembly platform. The resulting membrane protrusions continue to grow into the cytoplasm of the mating partner, traverse the cytoplasm in anti-parallel directions and make contact with the plasma membrane that flanks the mating junction. This investigation reveals the details of a novel, developmentally-induced mechanism of membrane disruption and restoration associated with pronuclear exchange and fertilization in the ciliate, Tetrahymena thermophila.

Development of dynamic behavior of the novel compositeT-joints: Numerical and experimental

In this paper dynamic behavior (modal analysis and dynamic transient response) of a novel sandwich T-joint is numerically and experimentally investigated. An epoxy adhesive is selected for bonding purpose and making the step wise graded behavior of adhesive region. The effect of the step graded behavior of the adhesive zone on dynamic behavior of a sandwich T-joint is numerically studied. Finite element analysis (FEA) of the T-joints with carbon fiber reinforced polymer (CFRP) face-sheets is performed by ABAQUS 6.12-1 FEM code software. Modal analysis and dynamic half-sine transient response of the sandwich T-joint are presented in this paper. Two verification processes employed to verify the dynamic modeling of the manufactured sandwich panels and T-joint modeling. It has been shown that the step wise graded adhesive zone cases have changed the second natural frequency by about 5%. Also, it has been shown that the different arranges in the step wise graded adhesive zone significantly affect the maximum stresses due to transient dynamic loading by 1112% decrease in maximum peel stress and 691.9% decrease in maximum shear stress on the adhesive region.

Tendon Adhesions: A Novel Method of Objectively Measuring Adhesions by Assessing Tendon Glide Through a Soft Tissue Envelope in a Rat Model.

To develop a rat model of extra-synovial tendon adhesions that will enable accurate testing of scar barriers and adhesion inhibiting treatments to facilitate future research. Thirty-six 6-month-old male Sprague-Dawley rats were randomized to one of the 3 groups of 12. In Group A, the middle one-third portion of the left Achilles tendon was excised. In Group B, the tendon and soft tissue bed was abraded with steel wool. In Group C, a silk suture was sewn along the tendon. The right hind limbs served as controls. At 4 weeks, biomechanical testing was performed on the bilateral hind limbs. The Achilles tendon was cut at the gastrocnemius-tendon junction proximal to the "adhesion zone" (or analogous level in the control limb). The calcaneal insertion of the Achilles was attached to a tensiometer. The force needed to pull the tendon out of its soft tissue envelope at a fixed rate was measured. Three rats were excluded because of complications during data collection. Pair-wise comparison testing was performed, comparing the mean peak force to pull the Achilles tendon from its soft tissue envelope in 33 control limbs and the contralateral limb from each group. The average peak force for the cut tendon group (A) was 20.1 N, 18.8 N in the steel wool group (B), and 21.1 N in the suture group (C). The average peak force in the control limbs was 15.6 N. There was a significant difference noted in peak forces between the control limbs and each experimental group. A consistent and statistically increased force was necessary to pull a rodent Achilles tendon from an adhesion-induced tissue bed compared with controls. No statistical difference was detected between experimental groups. Our study demonstrates an objective method of biomechanical tendon adhesion assessment in a rat model.

Membrane-Mediated Cooperativity of Proteins.

Besides direct protein-protein interactions, indirect interactions mediated by membranes play an important role for the assembly and cooperative function of proteins in membrane shaping and adhesion. The intricate shapes of biological membranes are generated by proteins that locally induce membrane curvature. Indirect curvature-mediated interactions between these proteins arise because the proteins jointly affect the bending energy of the membranes. These curvature-mediated interactions are attractive for crescent-shaped proteins and are a driving force in the assembly of the proteins during membrane tubulation. Membrane adhesion results from the binding of receptor and ligand proteins that are anchored in the apposing membranes. The binding of these proteins strongly depends on nanoscale shape fluctuations of the membranes, leading to a fluctuation-mediated binding cooperativity. A length mismatch between receptor-ligand complexes in membrane adhesion zones causes repulsive curvature-mediated interactions that are a driving force for the length-based segregation of proteins during membrane adhesion.

Indentation of adhesive beams

We investigate the contact of a rigid cylindrical punch with an adhesive beam mounted on flexible end supports. Adhesion is modelled through an adhesive zone model. The resulting Fredholm integral equation of the first kind is solved by a Galerkin projection method in terms of Chebyshev polynomials. Results are reported for several combinations of adhesive strengths, beam thickness, and support flexibilities characterized through torsional and vertical translational spring stiffnesses. Special attention is paid to the important extreme cases of clamped and simply supported beams. The popular Johnson–Kendall–Roberts (JKR) model for adhesion is obtained as a limit of the adhesive zone model. Finally, we compare our predictions with preliminary experiments and also demonstrate the utility of our approach in modeling complex structural adhesives.

Microstructure Evolution of Copper Strip during Continuous Extrusion and Rolling Forming

During the continuous extrusion and rolling forming process, the microstructure evolution of copper strip was investigated by the optical microscope and transmission electron microscope. The results indicated that the grains in the centre of as-cast rod billet were squashed in the clamping zone and were elongated in the rigid mobile zone. The fibrous structure formed in the upsetting zone. In the adhesion zone, the dynamic recrystallization occurred and the shear band was found. In the right-angle bending zone, the fibrous structure, recrystallized grains and shear bands existed together. The full dynamic recrystallization occurred in the extending extrusion zone. After continuous extrusion forming, the size of the grains of copper strip was larger than that in the extending extrusion zone. After rolling, the grains in copper strip were evidently stretched along the rolling direction, which resulted in the formation of stable direction. With the increase of rolling reduction, the grains were squashed gradually. When the rolling reduction increased from 2 to 6 mm, the tensile strength increased from 250 to 400 MPa, and the elongation decreased from 48% to 13%.

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.