scholarly journals A Design Strategy for Mushroom-Shaped Microfibrils With Optimized Dry Adhesion: Experiments and Finite Element Analyses

2020 ◽  
Vol 88 (3) ◽  
Author(s):  
Xuan Zhang ◽  
Yue Wang ◽  
René Hensel ◽  
Eduard Arzt
Keyword(s):  
Flat Glass ◽  
Interfacial Crack ◽  
Adhesive Force ◽  
Interfacial Stress ◽  
Design Parameters ◽  
Stress Distributions ◽  
Polymeric Surfaces ◽  
Interfacial Cracks ◽  
Dry Adhesion ◽  
Stalk Diameter

Abstract Enhanced dry adhesion of micropatterned polymeric surfaces has been frequently demonstrated. Among the design parameters, the cap geometry plays an important role to improve their performance. In this study, we combined experiments on single polyurethane mushroom-shaped fibrils (with a stalk diameter of 80 µm and height of 125 µm) against flat glass, with numerical simulations implementing a cohesive zone. We found that the geometry of the mushroom cap strongly affects the interfacial crack behavior and the pull-off stress. The experimental and numerical results suggest that optimal adhesion was accompanied by the appearance of both edge and interior interfacial cracks during separation. Finite elemental analyses revealed the evolution of the interfacial stress distributions as a function of the cap thickness and confirmed the distinct detachment mechanisms. Furthermore, the effect of the stalk diameter and the Young's modulus on the adhesive force was established, resulting in an optimal design for mushroom-shaped fibrils.

Technique to Measure Adhesive Forces Between Electrospun Nanofibers

2009 ◽  
Vol 1240 ◽  
Author(s):  
Qiang Shi ◽  
Kai-Tak Wan ◽  
Shing-Chung Wong ◽  
Pei Chen ◽  
Todd A. Blackledge
Keyword(s):  
Unit Area ◽  
Fiber Diameter ◽  
Electrospun Nanofibers ◽  
Amorphous Region ◽  
Adhesive Force ◽  
Degree Of Crystallinity ◽  
Scanning Calorimetry ◽  
Ultrafine Fibers ◽  
Dry Adhesion ◽  
Adhesive Forces

AbstractDue to the difficulty in handling nanofibers, little is reported and understood on the dry adhesion between electrospun nanofibers. In this study, we develop a technique to measure the dry adhesive forces between electrospun nanofibers. Of critical importance is the ability to mimic naturally occurring dry adhesion such as that between gecko's and spider's foot hairs and untreated surfaces. The adhesion test was performed on two poly(e-caprolactone) electrospun ultrafine fibers using a nanoforce tensile tester. It was found that the adhesive force per unit area increased with decreasing fiber diameter. The degree of crystallinity, order parameters of macromolecules in the amorphous region and crystallite orientation of the spun fibers were determined by the differential scanning calorimetry (DSC) and wide angle X-ray diffraction (WAXD). The high measured adhesion between single PCL fibers in comparison to other reported values was attributed to crystal orientation due to electrospinning and the increase of adhesive force per unit area with decreasing fiber diameter.

scholarly journals Finite-Element Simulation of Residual Stresses During the Processing of Lumped Burnable Absorber Fuel

2021 ◽  
Vol 9 ◽  
Author(s):  
Qusai Mistarihi ◽  
Ho Jin Ryu
Keyword(s):  
Finite Element ◽  
Threshold Stress ◽  
Initial Density ◽  
Interfacial Stress ◽  
Spherical Particles ◽  
Stabilized Zirconia ◽  
Interfacial Cracks ◽  
Element Simulation ◽  
Shielding Factor ◽  
Burnable Absorber

UO2–Gd2O3 fuel is mostly used as a burnable absorber fuel in the form of a homogenous mixture of Gd2O3 and UO2. More effective reactivity control can be achieved by lumping Gd2O3 within the UO2 because this enhances the spatial self-shielding factor of the burnable absorber fuel. The fabrication of lumped burnable absorber fuel containing lumped Gd2O3 spherical particles or compacts has been experimentally demonstrated using yttrium-stabilized zirconia (YSZ) as a UO2 fuel surrogate. Interfacial cracks or gaps forming under the interfacial stress that develops during the fabrication of the fuel can be eliminated by controlling the initial density of the lumped Gd2O3. In this study, this interfacial stress during the fabrication process was simulated using finite element methods. The effect of the size, shape, and initial density of the lumped Gd2O3 on the distribution and magnitude of the interfacial stress was investigated. The addition of Gd2O3 spherical particles resulted in a lower and more uniform interfacial stress distribution than the addition of cylindrical Gd2O3 compacts. The interfacial stress was increased with increasing Gd2O3 size and initial density. The calculated interfacial stress was compared with experimental results to estimate the threshold stress for crack development in a lumped burnable absorber fuel.

Effect of Thermal Residual Stresses on Polymer/Metal Interfacial Adhesion

1999 ◽  
Author(s):  
Qizhou Yao ◽  
Jianmin Qu
Keyword(s):  
Residual Stress ◽  
Residual Stresses ◽  
Coefficient Of Thermal Expansion ◽  
Interfacial Crack ◽  
Thermal Residual Stress ◽  
Element Analysis ◽  
Thermal Residual Stresses ◽  
Interfacial Cracks ◽  
Cte Mismatch ◽  
Elastic Mismatch

Abstract In this study, the apparent fracture toughness of the interfaces of several epoxy-based polymeric adhesives and metal (aluminum) substrate is experimentally measured. Double layer specimens with initial interfacial cracks are made for four-point bending tests. Thermal residual stresses exist on the interface due to the coefficient of thermal expansion (CTE) mismatch between the underfill and aluminum. Silica fillers are used to modify the CTE of the epoxy-based adhesives so that various levels of interface thermal residual stresses are achieved. Finite element analysis is also performed to quantify the effects of CTE mismatch as well as the elastic mismatch across the interface. It is found that the apparent interfacial toughness is significantly affected by the thermal residual stress, while the effect of elastic mismatch is negligible. In general thermal residual stress undermines the resistance to an interfacial crack. In some cases the residual stress is sufficient to result in adhesive and/or cohesive failure.

A two-term stress function approach to evaluate stress distributions in bonded joints of different geometries

2002 ◽  
Vol 37 (5) ◽  
pp. 385-398 ◽  
Author(s):  
P Lazzarin ◽  
M Quaresimin ◽  
P Ferro
Keyword(s):  
Elastic Properties ◽  
Stress Function ◽  
Function Approach ◽  
Design Parameters ◽  
Bonded Joints ◽  
Stress Distributions ◽  
Singular Stress ◽  
Generalized Stress Intensity Factors ◽  
Singular Stress Field ◽  
Singular Stress Fields

The paper presents a method for the evaluation of the singular stress fields in bonded joints of different geometries. The stress distributions are represented by a two-term stress expansion, under the hypothesis that both the first and the second terms are in the variable separable form. The method is based on the stress function approach, where the formulation is completed analytically and the resulting set of ordinary differential equations is solved numerically. The capability of the formulation to account for the actual elastic properties of the substrates allows an accurate description of the singular stress field to be obtained even in the case of joints made of materials with comparable elastic properties. The influence of adhesive joint design parameters such as the type of joint, geometry and material properties on the generalized stress intensity factors will also be presented and discussed.

Interfacial stresses in reinforced concrete cantilever members strengthened with fibre-reinforced polymer laminates

2019 ◽  
Vol 23 (2) ◽  
pp. 277-288 ◽  
Author(s):  
Xue-jun He ◽  
Chao-Yang Zhou ◽  
Yi Wang
Keyword(s):  
Reinforced Concrete ◽  
Interfacial Stress ◽  
Design Parameters ◽  
Stress Concentrations ◽  
Concentrated Load ◽  
Interfacial Stresses ◽  
Simply Supported ◽  
Reinforced Polymer ◽  
Fibre Reinforced Polymer ◽  
Polymer Laminates

Fibre-reinforced polymers have been increasingly used to strengthen reinforced concrete structures. However, premature brittle debonding failures may occur at the ends of externally bonded fibre-reinforced polymer laminates due to interfacial stress concentrations caused by stiffness imbalances. Although many studies exist on fibre-reinforced polymer-strengthened simply supported beams and slabs, the interfacial stress distributions in fibre-reinforced polymer-strengthened cantilever members are very different from those in simply supported members. Based on the assumptions of linear elasticity, deformation compatibility and static equilibrium conditions, the interfacial stresses in fibre-reinforced polymer-strengthened reinforced concrete cantilever members under arbitrary linear distributed loads were analysed. In particular, closed-form solutions were obtained to calculate the interfacial stresses under either a uniformly distributed load or a single concentrated load located at the overhanging end of the cantilever member. Existing test results on cantilever slabs strengthened by carbon fibre–reinforced polymer sheets were used to verify the model. According to the parametric analysis, the maximum interfacial stresses can be reduced by decreasing the fibre-reinforced polymer thickness, increasing the fibre-reinforced polymer bonding length and increasing the adhesive layer thickness, and by using less rigid fibre-reinforced polymer laminates with high tensile strengths. These results are useful for engineers seeking to optimize strengthening design parameters and implement reliable debonding prevention measures.

Strength and Fracture Characteristics of SUS304/AL-Alloy Scarf Adhesive Joint with Various Adhesive Thicknesses

2011 ◽  
Vol 462-463 ◽  
pp. 768-773 ◽  
Author(s):  
Mohd Afendi ◽  
Tokuo Teramoto ◽  
Akihiro Matsuda
Keyword(s):  
Fracture Toughness ◽  
Stress Singularity ◽  
Interfacial Crack ◽  
Uniaxial Tensile ◽  
Al Alloy ◽  
Stress Distributions ◽  
Mode Mixity ◽  
Adhesively Bonded ◽  
Fracture Characteristics ◽  
Scarf Joints

In this study, strength and fracture toughness of epoxy adhesively bonded scarf joints of dissimilar adherends, namely SUS304 stainless steel and YH75 aluminium alloy are examined on several scarf angles and various bond thicknesses under uniaxial tensile loading. Scarf angles, θ = 45°, 60° and 75° are employed. The bond thickness, t between dissimilar metals is controlled to be ranged between 0.1 mm to 1.2 mm. Finite element (FE) analysis is also executed to investigate the stress distributions in the scarf joints by ANSYS 11 code. From analytical solutions, stress singularity exists most pronouncedly at the steel/adhesive interface corner of joints having 45° to 75° scarf angle. This is not only in agreement with the FE analyses results but also confirmed by fracture surfaces observation wherein the fracture has always been initiated at this point. The strength of scarf joints increases as the bond thickness decreases. Interface corner toughness, Hc approach can be applied when predicting the failure stress of scarf joints. Besides, for scarf joints with an interfacial crack, the fracture toughness, Jc values are independent of bond thickness and less sensitive to adherends. Moreover, Jc increases as mode mixity increases.

Tooth contact analysis of a curvilinear gear set with modified pinion tooth geometry

2011 ◽  
Vol 225 (4) ◽  
pp. 975-986 ◽  
Author(s):  
Y-C Chen ◽  
M-L Gu
Keyword(s):  
Finite Element ◽  
Transmission Error ◽  
Contact Analysis ◽  
Design Parameters ◽  
Stress Distributions ◽  
Tooth Contact Analysis ◽  
Tooth Contact ◽  
Numerical Examples ◽  
Bearing Contact ◽  
Parallel Axis

This article investigated the contact behaviours of a modified curvilinear gear set for parallel-axis transmission, which exhibits a pre-designed parabolic transmission error (TE) and localized bearing contact. The proposed gear set is composed of a modified pinion with curvilinear teeth and an involute gear with curvilinear teeth. Tooth contact analysis enabled the authors to explore the influences of assembly errors and design parameters on TEs and contact ellipses of this gear set. It is observed that TEs were continuous and the contact ellipses were localized in the middle of the tooth flanks, even under assembly errors. Finite-element contact analysis was performed to study stress distributions under different design parameters. In addition, numerical examples are presented to demonstrate the contact characteristics of the modified curvilinear gear set.

scholarly journals Stress Intensity Factor for Interface Cracks in Bimaterials Using Complex Variable Meshless Manifold Method

2014 ◽  
Vol 2014 ◽  
pp. 1-8 ◽  
Author(s):  
Hongfen Gao ◽  
Gaofeng Wei
Keyword(s):  
Stress Intensity Factor ◽  
Stress Intensity ◽  
Intensity Factor ◽  
Complex Variable ◽  
Interfacial Crack ◽  
Dissimilar Materials ◽  
Complex Stress ◽  
Interface Cracks ◽  
Interfacial Cracks ◽  
Crack Problems

This paper describes the application of the complex variable meshless manifold method (CVMMM) to stress intensity factor analyses of structures containing interface cracks between dissimilar materials. A discontinuous function and the near-tip asymptotic displacement functions are added to the CVMMM approximation using the framework of complex variable moving least-squares (CVMLS) approximation. This enables the domain to be modeled by CVMMM without explicitly meshing the crack surfaces. The enriched crack-tip functions are chosen as those that span the asymptotic displacement fields for an interfacial crack. The complex stress intensity factors for bimaterial interfacial cracks were numerically evaluated using the method. Good agreement between the numerical results and the reference solutions for benchmark interfacial crack problems is realized.

scholarly journals Mechanics Of Interfacial Crack Propagation In Microscratching

1996 ◽  
Vol 436 ◽  
Author(s):  
Maarten P. de Boer ◽  
John C. Nelson ◽  
William W. Gerberich
Keyword(s):  
Thin Film ◽  
Mechanical Properties ◽  
Grain Boundary ◽  
Interfacial Crack ◽  
Strain Energy Release ◽  
Linear Elastic ◽  
Interfacial Cracks ◽  
Bending Strain ◽  
Diamond Indenter ◽  
Boundary Fracture

AbstractA new probing technique has been developed to test thin film mechanical properties. In the Microwedge Scratch Test (MWST), a wedge shaped diamond indenter tip is drawn along a fine line, while simultaneously being driven into the line. We compare microwedge scratching of Zone 1 and Zone T thin film specimens of sputtered W on SiO2. Symptomatic of its poor mechanical properties, the Zone 1 film displays three separate crack systems. Because of its superior grain boundary strength, the Zone T film displayed only one of these - an interfacial crack system. Using bimaterial linear elastic fracture mechanics, governing equations are developed for propagating interfacial cracks, including expressions for strain energy release rate, bending strain, and mode mixity. Grain boundary fracture strength information may be deduced from the Zone 1 films, while adhesion may be inferred from the Zone T films.

Collinear and Periodic Electrode-Ceramic Interfacial Cracks in Piezoelectric Bimaterials

2004 ◽  
Vol 71 (4) ◽  
pp. 486-492 ◽  
Author(s):  
Christoph Ha¨usler ◽  
Cun-Fa Gao ◽  
Herbert Balke
Keyword(s):  
Mixed Boundary ◽  
Piezoelectric Materials ◽  
Crack Problem ◽  
Interfacial Crack ◽  
Mixed Boundary Conditions ◽  
Interfacial Cracks ◽  
Field Intensity Factors ◽  
Work Done ◽  
Electric Loads ◽  
Relevant Work

Field singularities of collinear and collinear periodic interface cracks between an electrode and a piezoelectric matrix are studied in terms of the Stroh formalism for mixed boundary conditions. In contrast to the relevant work done previously on this subject, the problem is solved based on the assumption that the upper and lower planes embedding the electrode consist of two arbitrary piezoelectric materials, and the cracks are assumed to be permeable. The problem is reduced to an interfacial crack problem equivalent to that in purely elastic media. Explicit expressions are presented for the complex potentials and field intensity factors. All the field variables exhibit oscillatory singularities, and their intensities are dependent on the material properties and the applied mechanical loads, but not on the applied electric loads.

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