Adhesion Zone Research Articles

Understanding adhesive sliding nanocontact mechanics in an exponentially graded coating–substrate structure

The objective of this study is to investigate the frictionally adhesive nanocontact characteristics between a sliding rigid cylinder and an exponentially graded coating–substrate structure. Adhesive forces are modeled using the Maugis–Dugdale adhesive theory, while the Steigmann–Ogden surface mechanical theory describes the surface effects of the graded coating. Within the contact region, normal and tangential tractions adhere to the extended Amontons’ friction law. The governing equations and boundary conditions of the nanocontact problem are reformulated into Fredholm integral equations, which are solved numerically using Gauss–Jacobi quadratures and a self-designed iterative algorithm. Validation against existing literature results demonstrates the accuracy and reliability of the proposed solution method and numerical algorithm. Extensive parametric studies are conducted to investigate the effects of various parameters, including surface material properties, coefficient of friction, Tabor’s parameter, inhomogeneity index of the exponentially graded coating, and external loads. Results reveal that sliding friction significantly influences adhesive nanocontact, affecting nanocontact boundaries, contact traction distribution, and adhesive region boundaries. Additionally, surface effects play a crucial role, leading to smaller nanocontact length and maximum pressure but larger adhesive zone. Furthermore, the interplay between sliding friction, surface effects, and adhesion is underscored, emphasizing the importance of considering these factors in the analysis of sliding nanocontact problems involving graded materials. Ultimately, this work provides a comprehensive solution framework for addressing such complex nanocontact scenarios, offering insights valuable to the field of materials science and engineering.

Acoustic emission analysis of seizure transition process between steel journals and aluminum alloy plain bearings

Seizure tests were conducted using a bearing tester to elucidate the mechanism of seizure occurring between aluminum alloy (Al-Sn-Si) plain bearings widely used in gasoline engines and steel journals. Differences in torque spikes that occurred before seizure and final seizure were determined by analyzing the sliding surfaces and cross sections and the acoustic emission signal. The results revealed that the occurrence of final seizure was affected by the melting out and depletion of tin in the bearing alloy, plastic deformation due to frictional heat, and expansion of the aluminum adhesion zone caused by these factors.

Manufacturing of composites with designed failure

Abstract The failure of polymer composites is a very complex process, which mainly occurs as a result of interactions between different types of damage in the material, often at random locations and without any particular signs. To increase the reliability of composites and enable their wider use in safety-critical components, it is crucial to make their failure processes more controllable and predictable, which could be achieved by the local modification of the interfacial adhesion. The aim of our research is to develop and investigate a method for designing the failure process of polymer composites in terms of the location and the mode of failure. We produced interfacially engineered composites containing a weakened adhesion zone by adding polycaprolactone (PCL) thermoplastic interlayer material, which was applied directly on the surface of the reinforcing material by fused filament fabrication (FFF). Then, material tests were carried out, and the failure mode and position were evaluated as a function of the geometry of the interlayer material.

Cooling Air Velocity on Iron Ore Pellet Performance Based on Experiments and Simulations

During the pellet cooling process, cooling air velocity is crucial for optimizing the cooling rate, evaluating the utilization rate of cooling heat energy, and improving pellet performance. As the simulated cooling air velocity increased, the gas temperature at the cooling endpoint decreased from 87 °C to 51 °C, and the solid temperature decreased from 149 °C to 103 °C. The total enthalpy of the recovered gas initially reduced and then increased while the heat recovery rate gradually increased. During the experiment, the inhomogeneity of pellet quality gradually increased with the rise in cooling air velocity. The effect of cooling air velocity on pellet properties is primarily reflected in the formation of cracks and low-melting liquid phases (FeO and fayalite). As the cooling air velocity increases, the softening onset temperature of the pellet decreases significantly. The melting zone decreases from 193 °C to 105 °C, and the permeability of the adhesive zone increases.

Lap-Shear Performance of Weld-Bonded Mg Alloy and Austenitic Stainless Steel in Three-Sheet Stack-Up

With the growing interest in utilizing Mg and austenitic stainless steel (ASS) in the automotive sector, joining them together in three-sheet configuration is inevitable. However, achieving this task presents considerable challenges due to the large differences in their physical, metallurgical and mechanical properties. To overcome these challenges, the feasibility of using weld-bonding to join Mg alloy/ASS/ASS was investigated. The nugget formation, interface characteristics, microstructure and mechanical properties of the joints were investigated. The results show that the connection between the Mg alloy and upper ASS was achieved through the combined effect of the cured adhesive and weld-brazing in the weld zone. On the other hand, a metallurgical bond was formed at the ASS/ASS interface. The Mg nugget microstructure exhibited fine columar grains composed predominantly of primary α-Mg grains along with a eutectic mixture of α-Mg and β-Mg17Al12. The nugget formed at the ASS/ASS interface consisted largely of columnar grains of austenite, with some equiaxed dendritic grains formed at the centerline of the joint. The weld-bonded joints exhibited an average peak load and energy absorption of about 8.5 kN and 17 J, respectively (the conventional RSW joints failed with minimal or no load application). The failure mode of the joints changed with increasing welding current from interfacial failure via the Mg nugget/upper ASS interface to partial interfacial failure (part of the Mg nugget was pulled out of the Mg sheet). Both failure modes were accompanied by cohesive failure in the adhesive zone.

Investigation on the joining process and strength of laser circle welding between Al5052 and CFRP dissimilar materials

Laser welding is an effective approach to joining metal and composite. In the present research, laser circle welding was proposed to join the Al5052 sheet and PA6-CFRP as the first try. A process window was suggested according to the welding results and joint appearance. Single lap shear test was employed to evaluate the mechanical performance of welded joints under different welding conditions. The cross-section and fracture surface were subjected to multi-scale characterizations to subdivide the joining zone and understand the joining process. The result showed that 10 sets in 18 groups of welding parameters can achieve successful bonding. The welding results can be classified into four categories: non-connected, aging-failing, effective-joining and burn-through. The joining zone of laser circle welding was divided into three subregions. The adhesive zone (AZ) presented an interfacial fracture while the local failing passed through plastics basement in cohesive (CZ). The overheating of CFRP generated decomposed zone (DZ). The signal peak of O-C=O bond disappeared in the entire joining zone on CFRP sheet and the intensity of carbide was significant in DZ. The laser circle welded joint presented brittle and ductile fracture modes, which were related to the joining zone component. The joining strength can reach about 656 ± 22 N, 2135 ± 331 N and 3223 ± 257 N under one-circle, double-circle and three-circle scanning, respectively. Increased scanning numbers can decrease the required laser power and improve joining strength by extending heating time, while it also increased the risk of burn-through.

Investigation of the Fracture Behaviour of Al-CFRP Cross-Lap Joint Fabricated by Coaxial One-Side Resistance Spot Welding.

In the present research, coaxial one-side resistance spot welding was performed to join Al5052 and CFRP sheets with different welding currents. The mechanical performance of the cross-lap joint was clarified experimentally. The cross-section of the welded joint and the fracture surfaces was subjected to multi-scale characterization. The fracture behaviours and mechanisms of cross-lap joints are discussed in detail. The results showed that the thermal degradation of CFRP was detected on the cross-section under a 6000 A welding current and the O element was enriched in the decomposed area. The joining zone could be divided into four subregions according to their morphology, which were defined, from outside to inside, as the squeezed zone, the adhesion zone, the cohesion zone and the decomposed zone. After welding, the O-C=O bond disappeared on the CFRP surface while the O=C-N bond was detected on the Al5052 surface. The cross-lap joints demonstrated brittle and ductile fracture behaviours in a cross-tension test, which included two sub-modes: brittle-transition mode and ductile-degradation mode. The transformation of failure modes had a relationship with the heat input and corresponding joining zone composition. The maximum cross-tension load was about 1279 ± 40 N with a welding current of 5600 A.

Prediction of fatigue crack behaviour of carbon fibre reinforced asphalt using fracture testing and modelling of the adhesive zone CZM

ABSTRACT Mechanical behaviour and fatigue failure characteristic of asphalt mixtures is complex under cyclic loading conditions and require better recognition due to the importance of these infrastructures. Fatigue tests are usually time-consuming, expensive, and require experience. These challenges increase when the mixtures contain a variety of additives that complicate the recognition of material behaviour. In this study, carbon fibres were investigated as additives with high tensile strength. After failure tests on SCB samples(5 different percentages of fibres and 5 different lengths), 1.5% fibres and 15 mm length were used as optimum values for other experiments for 3 fracture models (I,II, and mixed I&II modes). Monotonic and cyclic failure tests of mixtures containing carbon fibres are presented by Abaqus modelling to predict fatigue behaviour of these materials. For this purpose, the Cohesion Zone Model (CZM) was selected for modelling and the failure parameters obtained from the experiments were validated by the results of the modelling. Comparison of experimental and modelling results in the study of mulmouthle outputs indicates that the predicted and measured fatigue behaviour have good conformity. Achieving such models reduces the need for expensive and time-consuming experiments and provides a useful tool for examining other effective parameters.

Vesicle condensation induced by synapsin: condensate size, geometry, and vesicle shape deformations

We study the formation of vesicle condensates induced by the protein synapsin, as a cell-free model system mimicking vesicle pool formation in the synapse. The system can be considered as an example of liquid–liquid phase separation (LLPS) in biomolecular fluids, where one phase is a complex fluid itself consisting of vesicles and a protein network. We address the pertinent question why the LLPS is self-limiting and stops at a certain size, i.e., why macroscopic phase separation is prevented. Using fluorescence light microscopy, we observe different morphologies of the condensates (aggregates) depending on the protein-to-lipid ratio. Cryogenic electron microscopy then allows us to resolve individual vesicle positions and shapes in a condensate and notably the size and geometry of adhesion zones between vesicles. We hypothesize that the membrane tension induced by already formed adhesion zones then in turn limits the capability of vesicles to bind additional vesicles, resulting in a finite condensate size. In a simple numerical toy model we show that this effect can be accounted for by redistribution of effective binding particles on the vesicle surface, accounting for the synapsin-induced adhesion zone.Graphic abstract

Research on wheel-rail dynamic interaction of high-speed railway under low adhesion condition

Due to the inherent openness of the wheel-rail system, the wheel-rail interface is subject to the influence of a third medium, resulting in a low adhesion state. This study investigates the dynamic interaction between the wheel and rail under low adhesion conditions through the development of a numerical model employing anti-skid control strategies and infinite long track simulation technology. The model's validity is established by comparing its calculations with data from both the multi-body dynamics software UM and field tests. The numerical simulations uncover that the implementation of rail side lubrication significantly reduces longitudinal creep forces, thereby diminishing the wheelset's steering capabilities. Furthermore, it induces a notable increase in lateral wheel-rail interaction, consequently lowering safety indicators in vehicle operations. Rail side lubrication is found to substantially reduce rail side wear, resulting in an approximate 60% decrease in the maximum wear depth. Comprehensive friction control on the rail surface concurrently mitigates rail side and top surface wear. In instances of local low adhesion on both sides, the wheelset experiences pronounced stick-slip vibrations, leading to a deterioration in the longitudinal dynamic performance between the wheel and rail. Unilateral low adhesion situations prompt noticeable yawing and shaking motions within the low adhesion zone, resulting in evident lateral impact phenomena. Upon re-entering the normal adhesion zone from the low adhesion zone, the rail wear index experiences a significant peak, which means that the rails in this area are prone to severe local wear or fatigue.

Study on the fretting wear performance and mechanism of GH4169 superalloy after various laser shock peening treatments

GH4169 nickel-based superalloy is often used in aero engines, it always suffer from complicated fretting wear behaviors in the service. To improve the fretting wear performance, laser shock peening (LSP) technology was selected in this paper, the fretting wear properties, and mechanism of GH4169 superalloy following treatments with high-energy LSP (HE-LSP), low-energy LSP (LE-LSP), and femtosecond LSP (FS-LSP) were studied. Under 7 N load, the wear rate of HE-LSP and FS-LSP decreases by 58.6 % and 26.2 % respectively, while the wear rate of LE-LSP increases by 25.9 %. Under 12 N load, the wear rate of HE-LSP and FS-LSP decreases by 42.9 % and 12.7 % respectively, while the wear rate of LE-LSP increases by 104.8 %. The wear rate of GH4169 superalloy decreases due to the interaction of surface hardening layer and debris accumulation layer. The increase in wear rate is due to the non-uniform ablative holes on the sample surface and microcracks in the matrix. After receiving the LSP treatment, GH4169’s wear mechanism shifted from adhesive wear to abrasive wear. LSP treatments can prevent the formation of adhesive zone because of the formation of a hardened layer and debris, and the increasing in tangential stiffness of the material. The HE-LSP technology has the best effect on the wear resistance of GH4169, followed by the FS-LSP treatment, while the LE-LSP treatment reduces the wear resistance of GH4169.

Influence of unilateral low adhesion on transient wheel-rail rolling contact and wheel damages

A time-domain finite element model is developed to study the transient rolling contact of a driving wheelset over a curved track with Low Adhesion Zones (LAZs) shorter than 1.0 m. LAZs on one rail, i.e., unilateral LAZs occurring more likely, is treated for a speed up to 500 km/h. Structural vibrations of wheelset are analyzed to explain the transient contact forces, creepages and the resulting irregular wear. LAZs on high rails are found more detrimental than those on low rails. The results explain the occurrence of flats and rolling contact fatigue in bad weather, although significant wheel idling is absent.

Understanding Platysma Muscle Contraction Pattern and Its Relationship to Platysmal Banding: A Real-Time Ultrasound Study.

Addressing neck contouring with surgical and nonsurgical aesthetic procedures includes understanding the origin of platysmal banding. A theory was postulated to explain this phenomenon by isometric vs isotonic muscular contraction patterns. However, no scientific proof had been provided to date for its correctness. The aim of this study was to confirm the correctness of the platysmal banding theory based on isometric vs isotonic muscular contractions. Eighty platysma muscles from 40 volunteers (15 males and 25 females) were investigated (mean age 41.8; SD 15.2 years; mean BMI of 22.2; SD 2.3 kg/m2). Real-time ultrasound imaging was utilized to measure the increase in local muscle thickness inside and outside of a platysmal band as well as platysma mobility. Within a platysmal band, the local thickness of the muscle increases during muscular contractions by 0.33 mm (37.9%; P < .001). Outside of a platysmal band the thickness of the platysma muscle decreased by 0.13 mm (20.3%; P < .001). It was identified that within a platysmal band no gliding was detectable, whereas outside of a band an average muscle gliding of 2.76 mm was observed. The results confirm the correctness of the isometric vs isotonic platysma muscle contraction pattern theory: isotonic muscle contraction (gliding without increase in tension and therefore in muscle thickness) vs isometric muscle contraction (no gliding but increase in tension and therefore in muscle thickness). These 2 types of contraction patterns occur within the platysma simultaneously and are an indicator for zones of adhesion in the neck to guide surgical and nonsurgical aesthetic procedures.

Visual Observation of Abdominal Adhesion Progression Based on an Optimized Mouse Model of Postoperative Abdominal Adhesions

Background: There is no clear description of the evolution of the progression of abdominal adhesions over time. Method: The optimized model was selected using different adhesion scoring systems. Then, this model was used to observe the progression of abdominal adhesions. Visualized observation of abdominal adhesion evolution was performed by laparoscopy and computed tomography. The inflammatory cell infiltration and collagen fibers in adhesion tissues at different times were evaluated by hematoxylin-eosin and picrosirius red staining. RNA sequencing was used to predict potential key targets of abdominal adhesions at different times. Results: The abdominal adhesion model showed the highest reproducibility when it was established using a circular tool and an electric brush. Based on this model, we found that the inflammatory response was activated early in the process of adhesion formation, peaking on day 3 and then gradually decreasing until stabilization on day 7. Collagen and fibronectin formed on day 1 and gradually increased until remaining stable on day 7. In addition, the characteristic changes in the adhesion zone from initial congestion, edema and fragile tissue to later dense and stable tissue could be vividly observed in live mice by laparoscopy and artificial pneumoperitoneum CT. The RNA sequencing results revealed that Hck on day 1, Ndufs3 and Ndufs8 on day 3 and Aif1 on day 7 might play key roles in abdominal adhesion formation. Conclusion: The construction of a standard process for describing the evolution of abdominal adhesions based on an optimized mouse model will help to facilitate subsequent adhesion-related studies.

Aesthetic Units and Zones of Adherence, Relevance to Planning Incisions in Body Contouring Surgery.

Aesthetic units (AUs) and zones of adherence (ZAs) have been previously noted in the face and torso. A systematic classification of common AUs and ZAs has not been previously described for the torso and extremities. Contour and scars are equally important in obtaining the best result. Therefore, the six principles to consider in body contouring surgery (BCS) are that the resulting scar be anchored at a zone of adhesion; at the interface of AUs; concealed within flexion or extension skin creases, or placed according to conventional usage and experience; positioned on the medial aspect of a limb; hidden when nude, topless, or in a variety of clothing such as one-piece and two-piece swimsuits, crop tops, short sleeves, etc; and positioned to avoid a contracture across a flexion joint crease or a dehiscence across the extension aspect of a joint. Images of male and female massive weight loss (MWL) patients with a history of MWL were reviewed and analyzed. AUs and Zas are described and codified. An algorithm is provided to aid in planning incisions for BCS. With the increase in BCS after MWL, a classification of AUs and ZAs is considered useful in planning surgery and optimizing the aesthetic result.

Indentation of geometrically exact adhesive beams

We investigate the indentation of thin adhesive beams by a rigid frictionless circular punch in two-dimensions through computations and experiments. A non-linear geometrically exact (GE) beam formulation that allows for arbitrarily large displacements and rotations is employed for the thin beam. The Karush–Kuhn–Tucker condition for unilateral contact is adapted to model adhesive interaction in a nonlinear finite element (FE) framework. In this, contact is enforced through a penalty method and adhesion is incorporated through two different cohesive zone models (CZMs), viz. exponential and bilinear. The indentation of the adhesive GE beam is then studied in terms of the variations of the applied force, the pressure distribution, the cross-sectional rotation and the sizes of the contact area and the adhesive zone for different indentation extents, adhesive strengths, punch radii, beam thicknesses and end supports. We find that the system is largely agnostic to the CZM utilized, as well as the type of end supports unless the contact area spans the beam. At the same time, thinner beams tend to initiate contact with a punch more easily, and are harder to detach. We then demonstrate that thin beams may undergo large rotations even if the indentation is small, which necessitates a nonlinear beam theory. Under such conditions approximating a circular punch by a parabolic one used typically when indentations are small introduces errors. Finally, we conduct experiments on clamped adhesive beams made of two different types of PDMS (polydimethylsiloxane) and various thicknesses, and find a good match with our computations.

Numerical and experimental study of the viscosity and mechanical parameters effect on tow feeding quality during automated fiber placement

For automated fiber placement (AFP), it is crucial to research the contact characteristics between tow and roller during the tow feeding process. However, it has not been widely explored. In this paper, a theoretical model of contact characteristics for the tow feeding process is established by analyzing the distribution of normal stress, tangential stress, adhesion zone, and slip zone, respectively. The model proposed a numerical algorithm for calculating the contact characteristic. Then the contact characteristic of the tow feeding system can be acquired and validated by the experiment and finite element method. The model that provides theoretical support for AFP optimization. Furthermore, proper pressure (P = 0.6Mpa) and tension (T = 3 N) for towpreg feeding under experimental conditions were obtained.

The effect of fiber length and structure on joint strength in bonded joints with fiber-reinforced composite adhesive

Today, composite materials are frequently used as materials in engineering due to their light weight and strength. Studies on the use of composite materials and the adhesively bonded joints used to bond these materials are of importance. In general, studies on the bonding method with adhesives are concerned with the strength of the joint. In this study, fiber fabric was reinforced to the bonding area in order to increase the strength of the bonding connections used in the aviation and automotive fields. DP460 structural adhesive as adhesive and AA2024-T3 aluminum alloy used in aviation field as bonded material were used to produce a single-lap joint bonded with adhesive. In addition, carbon fiber, glass fiber and aramid fiber fabric were used as reinforcing elements in the adhesive zone. Furthermore, to examine the effects of fiber fabric length in the overlap area at joint-failure load, four different length fiber fabric such as 100%, 80%, 40% and 20% of the overlap length were added. As a result, when the experimental failure loads were examined, the composite adhesive obtained by adding fibrous fabric has been found to increase the load failure of the joint between about 16% and 90%. However, increase rate in the failure load changes depending on the length fiber fabric and the type of fiber fabric. Moreover, in the geometries of single-lap joints produced in this study, the best fiber fabric type, in terms of the failure load of the joint, was carbon fiber fabric.

Comparative study on MQL milling and hole making processes for laser beam powder bed fusion (L-PBF) of Ti-6Al-4V titanium alloy

In this experiment, the laser powder bed fusion (L-PBF) formed prefabricated hole specimens were machined at a certain cutting speed by changing the feed rate and using the dry cutting and micro lubrication (MQL) assisted cutting process with the aim of improving the surface accuracy and quality of additively manufactured titanium alloy holes. The machining method of milling was used to compare and analyze the surface quality, cutting force, tool wear, and chip shape of the specimens under different machining processes. The results have shown that the actual dimensions of the original holes formed by L-PBF are generally smaller than the theoretical ones, mainly due to the collapsed areas and powder adhesion zones. The best machining quality of the hole structure was obtained with the feed rate of 20 mm/min and the MQL-assisted process. The burr was relatively minimal, with an average dimensional error of only 77 μm. The overall cutting forces are high and fluctuate during dry cutting. The MQL-assisted cutting process can significantly reduce the cutting forces compared with the dry cutting conditions, especially the radial cutting forces, during machining. At a feed rate of 10 mm/min, the overall maximum radial cutting force is reduced by 72 %, and the overall average axial cutting force is reduced by 35 %. At a feed rate of 30 mm/min, the overall maximum axial cutting force is reduced by 37 %. The tool wear was severe, and many chips adhered to the tool under dry-cutting conditions. The tool wear was significantly reduced under the MQL process, presumably because the atomized lubricant formed an oil film on the tool, powder, and substrate, significantly reducing friction and chip adhesion. In addition, under the oil film, the residual metal powder is like the ball in a ball bearing, significantly reducing the friction between the tool and the substrate.

Wheel wear prediction for high speed railway vehicles during acceleration

Wheel wear prediction for high-speed railway vehicles during the acceleration process is of great importance for the improvement of operating characteristics and the development of friction management strategy near the railway station, especially in complex climatic environments. This work analyzes and predicts the wheel wear evolution of high-speed motor cars during acceleration. Firstly, detailed dynamic models of the high-speed motor car are developed, in which a comprehensive gear transmission system is also adopted to capture the accurate dynamic responses of the motor car. Secondly, the length of the simulated track interval with different friction coefficients is set according to the Gaussian distribution function to consider the influence of the friction coefficient. Moreover, a Proportional-Integral(PI) creep controller is also introduced to meet the challenge due to varying wheel-rail contact conditions, and a wheel wear prediction model based on the aforementioned submodels is established to obtain the wheel wear evolution. Finally, simulation results of dynamic responses from the vehicle dynamic model and wheel wear prediction procedure are compared with the measured field data. The results show that the time-varying meshing stiffness from the gear transmission system will aggravate the interaction between wheel and rail and deteriorate the wheel wear. When the high-speed motor car passes through a poor adhesion zone in the acceleration, it is easier to trigger the creep controller at the low-speed period while it will not occur at the high-speed period.