Surface Roughness Of Adherends Research Articles

Effect of microstructural roughness on the performance and fracture mechanism of multi-type single lap joints

Surface roughness of adherends is a crucial factor in determining the performance and failure mechanism of adhesive joints. However, the research dedicated to the examination of fracture mechanism for adhesive joints influenced by surface roughness at microscale is limited. This work conducts systematic experimental and numerical investigations into the effect of microstructural roughness on the performance and fracture mechanism of multi-type adhesive single lap joints (SLJ). The adherend materials are aluminium alloy (Al) and polyphthalamide (PPA), ground into three roughness grades for the fabrication of SLJs using an epoxy adhesive. The mechanical properties of the adhesive, adherends and SLJs derived from experimental studies are utilized to calibrate the microparameters in Discrete Element Method (DEM) models for a numerical analysis. The newly developed DEM models demonstrate efficacy in predicting the performance and capturing the failure modes of multi-type SLJs realistically with distinct microroughness profiles. Finally, the influencing mechanisms of microstructural roughness on the performance of multi-type SLJs are investigated, including the microscale interfacial bonds and mechanical interlockings. The effects of microstructural roughness on the microscale failure mechanisms of multi-type SLJs are also explored and discussed, including the crack initiation, coalescence, and propagation within the adhesive and interface.

Adherend surface roughness effect on the mechanical response of silicone-based adhesive joints

The present contribution focuses on the effect of adherend surface roughness on the strength of adhesive joints, which are particularly cost-effective and extensively applied in a wide range of industrial applications. However, the reliability of such solutions is a critical concern for the integrity of commercial products. To gain a deeper understanding on the effect of roughness, an extensive experimental campaign is proposed, where thermoplastic substrates are produced with a specified roughness, whose characterization has been performed using a confocal profilometer. Elastic strips are then bonded onto such substrates using Silicone adhesive while controlling the adhesive thickness. Peeling tests are finally carried out and the effects of joint parameters such as surface roughness, adhesive thickness, and loading rate are discussed in detail. Eventually, it is demonstrated that the surface roughness can increase the adhesion energy of joints depending on the value of a ratio between the adhesive thickness and the root mean square elevation of roughness.

Analyzing effects of surface roughness, voids, and particle–matrix interfacial bonding on the failure response of a heterogeneous adhesive

An automated computational framework is introduced to link the microstructure to the micromechanical behavior of a heterogeneous adhesive composed of an epoxy matrix and embedded silica particles. A new reconstruction algorithm is employed to synthesize 3D periodic microstructural models of this materials system based on morphological and statistical data extracted from micro-computed tomography images. A non-iterative mesh generation algorithm is implemented in parallel to transform resulting virtual microstructures into finite element (FE) models. The continuum ductile and cohesive damage models used for simulating the adhesive’s failure response are calibrated with experimental data and the statistical representative volume element (SRVE) is identified. We have then carried out several high-fidelity FE simulations to investigate the effects of pre-existing voids in the adhesive layer, surface roughness of adherends, and the bonding strength along particles–matrix interfaces on the failure response of the adhesive subject to tensile, compressive, and shear loads.

Experimental study on different adherend surface roughness on the adhesive bond strength

In this study, an investigation on adherend surface roughness on adhesive bond strength was performed. The adherend materials used were mild steel and aluminium AA6063, whereas the adhesive used was an epoxy resin (Araldite® 2015). Surface of adherend materials were treated by the mechanical abrasion process using an emery paper of different grade to get different level of roughness. Single strap joints were tested at room temperature under tensile loading in Universal Testing machine. Results showed that optimum surface roughness values were found in the different range with respect to the adhered material joints.

Milling as a method of surface pre-treatment of steel for adhesive bonding

The paper analyses the impact of mechanical milling pre-treatment parameters on adhesive joint strength. Comparison of surface roughness of adherends after milling and its effect on adhesive joint strength is analysed in strength tests. The tests were performed on C45 structural steel specimens, which were subjected to machining at different parameters, with two types of milling cutters. Adherends were degreased prior to adhesive joining. Two types of end mills used in tests were NFPaφ20 high-speed steel cutter and R390-020B20-11L indexable milling cutter. The machining was carried out at three cutting speeds: 0.05, 0.15 and 0.30 mm/tooth. Adherends were joined with an adhesive composition of Epidian 57 epoxy resin and Z-1 curing agent.

Automated analysis of microstructural effects on the failure response of heterogeneous adhesives

Adhesive bonding enables the joining of thin and dissimilar materials, which is one of the main requirements for manufacturing lightweight structures in the automotive and aerospace industries. However, due to the small thickness and complex microstructure of the adhesive layer, which is often reinforced with embedded heterogeneities to improve its mechanical behavior, simulating the damage process in the adhesive can be a challenging task. In this work, we implement a computational cohesive model to quantify the effects of microstructural features such as particles volume fraction, pre-existing flaws, and surface roughness of adherends on the failure response of a heterogeneous adhesive with embedded glass particles. The hierarchical interface-enriched finite element method (HIFEM) is implemented as the main computational engine for simulating the initiation and propagation of damage in the adhesive layer. This mesh-independent method allows for using finite element meshes that are completely independent of the problem morphology, which considerably facilitates conducting multiple damage simulations for adhesive models with different microstructural features. We also introduce a new virtual prototyping algorithm and integrate that with the HIFEM to enable the automated construction of realistic models of the adhesive microstructure based on digital data.

Synthesis and Characterization of a Novel High-Temperature Structural Adhesive Based on MDA-BAPP-BTDA Co-Polyimide

A series of polyimide(PI) adhesives were synthesized from 2,2'-Bis [4-(4-aminophenoxy)phenyl] propane(BAPP), 4,4'-Diaminodiphenylmethane (MDA) and 3,3',4,4'-Benzophenonetetracarboxylic acid dianhydride (BTDA) via a two-step process. PI adhesives with different BAPP content were characterized in regard to their structure, thermal stability, mechanical properties and adhesive performance. Results showed that these PIs had excellent thermal stability, whose glass transition temperature (Tg) were around 300°C. While, superior dynamic mechanical behavior was observed, and the maximum loss factor declined with the increase of BAPP content. Single-lap shear strength of over 15.58 MPa at room temperature was obtained, and it remained high even at the temperature of 350°C. Factors that could affect bonding strength of these PI adhesives such as molar ratio of the diamine monomers, surface roughness of adherends and curing processes were investigated.

The effect of mode ratio and bond interface on the fatigue behavior of a highly-toughened epoxy

The fatigue threshold and the cyclic crack growth of a highly-toughened epoxy adhesive were studied under mode I and several mixed-mode loading cases and compared with the quasi-static critical fracture energies. Four different adhesive systems were examined using steel and aluminum substrates having different surface roughness, and surface treatment. The effect of increasing the amount of mode II (increasing the phase angle) on the fatigue threshold strain energy release rate and the cyclic crack growth rate was found to be insignificant at low phase angles. However, a significant increase in the fatigue threshold and decrease in the cyclic crack growth rate was observed at higher phase angles. These trends were similar to that seen in adhesive joint fracture. Adherend surface roughness and surface preparation affected the fatigue behavior significantly, particularly at low crack speeds and high phase angles. The fatigue properties were essentially the same for both steel and aluminum adherends provided that the crack paths were cohesive. A general observation was that the fatigue crack path moved progressively closer to the more highly strained adherend under mixed-mode loading as the applied strain energy release rate and hence the crack speed, decreased. This caused mixed-mode cracks to be nearly interfacial in the threshold region.

Effect of Adhesive Thickness on Joint Strength: A Molecular Dynamics Perspective

Recent studies suggest that adhesion in thin joints depends on several factors including temperature, interface toughness, strain rate, surface roughness of adherends, bondline thickness of adhesives, and many others. Influence of thickness on joint properties is surprising but experimentally well documented without reasonable explanations. In this study, we attempt to address the mechanical behavior of polymer adhesives by molecular dynamics (MD) simulation. We show that interfacial strength of the joints in tensile, shear, or combined loading significantly depends on the coupling strength between adhesives and adherends. Failure of joints is always at the interface when coupling strength is weaker. With stronger interfaces, cohesive failure occurs by cavitation or by bulk shear depending on the loading condition. When joints are loaded in tension, it requires an exceedingly stronger interface to realize pure shear failure, otherwise failure is through interface slip. Under a mixed mode condition, interface slip is difficult to avoid. As long as failure is not at the interface alone, the yield strength of joints improves significantly with the reduction of thickness. Increase in bulk density and change in polymer configurations with the reduction of adhesive thickness are believed to be the two key factors in improving mechanical behavior of adhesives.

A Modified Apparatus for Testing the Probe Tack of Pressure-Sensitive Adhesive Materials

A modified probe-tack test is described in which a special device is capable of detecting the first contact between the probe and a pressure-sensitive adhesive (PSA) and to determine this contact as the initial dwell time. In tests using viscoelastic PSA materials (hydrogels), this modified device gives results which differ significantly from those obtained with conventional probe-tack testers. In particular, when tack values are plotted against dwell time, the modified tester reveals a regime of sigmoid low-energy tack and then a transition to the normal power-law high-energy tack. This transition behavior was studied as a function of crosshead velocity, compression pressure, adhesive rheology and adherend surface roughness. The practical implication is that far more information can be obtained from this modified device than from conventional probe-tack testers. The modified machine and methodology should prove particularly valuable as an experimental tool and for quality-control tests in the manufacture of PSA products, particularly soft and tacky viscoelastic substances.

Study of the effect of substrate roughness on adhesive joints by SEM image analysis

The effect of adherend surface roughness on epoxy bonded aluminium joints has been studied. Several epoxy adhesives were tested to evaluate the influence of adhesive nature on the roughness effect. The aluminium pre-treatments applied were abrasion and impression processes, generating different texture levels. The abrasion with grinding papers of different grain sizes provides surfaces with high density of low summits. In contrast, the surfaces subjected to impression process present low density of very deep valleys. The roughness measurements were made by image analysis of micrographs obtained by Environmental Scanning Electron Microscopy (ESEM). In addition to the average roughness, other surface descriptors were determined to characterise completely the surfaces, allowing to evaluate the influence on the adhesive strength of different texture variables, such as the height, shape and density of the peaks and valleys which constitute the roughness profile. An optimum value of surface roughness was found for the joint strength measured by the lap shear tensile test. An increase of adherend roughness causes an increase of effective area but, at the same time, decreases the ability for adhesive penetration. It has also been shown that the joint strength depends on the main characteristics of the adherend surface, such as the density and depth of the protuberances. Finally, it has been found that the roughness effect seems be influenced by the adhesive nature. Different epoxy adhesives with similar mechanical properties present different joint strengths due to their different penetration abilities.

Testing the rolling tack of pressure-sensitive adhesive materials. Part II: Effect of adherend surface roughness

A novel method and custom-made apparatus for testing the rolling tack of pressure-sensitive adhesives (PSAs) and related materials were developed to measure bonding and debonding processes. The combined effects of adherend (probe) surface roughness, longitudinal load, and dwell time on bond-formation performance of five different tacky materials chosen from various application areas were studied. These materials included synthetic PSAs (acrylic tape and the hydrocolloid dressing, Granuflex®), water-remoistenable adhesive (CENTRAL®), edible wheat flour dough, and a static cling vinyl (PENSTIC®). Tack-rolling velocity curves were analyzed to study bonding and debondong processes. Each of the tested materials showed different tack behavior in response to varying probe roughness, external load, and velocity (dwell time). Surface wetting and mechanical interlocking were proposed as the mechanisms governing tack in most tested PSAs. Acrylic PSA tested on a smooth probe over a velocity range of 0.12-2.12 m/s showed higher tack values than on a rough one. A significant reduction in tack was due to restricted bond formation. Similarly, tack of Granuflex® to a smooth model skin surface showed higher values than to a rough skin surface. CENTRAL® showed typical cohesive failure when tested on silicone-coated paper. Interfacial failure and short-term bonding accounted for good tack performance on porous paper. Dough tested with aluminum probes showed cohesive failure similar to that of CENTRAL® at velocities higher than 0.2 m/s where the tack was independent of probe surface roughness. PENSTIC® adhered only to smooth glass where the tack values tended to decrease with increased velocity. Bonding and debonding processes of the various tacky materials were clearly affected by adherend surface roughness, longitudinal load, and dwell time, and could be successfully analyzed using our novel proposed method and apparatus.

The effects of surface roughness and bond thickness on the fatigue life of adhesively bonded tubular single lap joints

Since the surface roughness of adherends greatly affects the strength of adhesively bonded joints, the effect of surface roughness on the fatigue life of adhesively bonded tubular single lap joints was investigated analytically and experimentally by a fatigue torsion test. The stiffness of the interfacial layer between the adherends and the adhesive was modelled as a normal statistical distribution function of the surface roughness of the adherends. From the investigation, it was found that the optimum surface roughness of the adherends for the fatigue strength of tubular single lap joints was dependent on the bond thickness and applied load.

Thermoplastic bonding to metals via injection molding for macro‐composite manufacture

AbstractIn this work, we explore a new method of in‐situ joining of polymers to metals in injection molding to allow direct bonding between thermoplastic and metal parts. Such a method can integrate several downstream steps in product manufacture, allow optimal design of products and joints, and avoid adhesive application, assembly, and associated difficlties. A variety of process parameters and their effects upon the interface tensile strengths were examined. A full factorial experiment was conducted involving four of the critical process parameters identified. The effects upon tensile strength at break of the following process parameters were studied: (1) adherend surface temperature, (2) screw linear velocity, (3) bondline thickness, and (4) pack and hold pressure. The fracture surfaces and the thermoplastic metal interfaces were analyzed. The bonds fabricated with higher adherend surface temperatures have increased mean tensile strength and less adhesive failure. This increase in mean bond tensile strength and less adhesive failure was due to increased polymer penetration of the adherend surface roughness, at the micrometer level, as shown in the analysis of the polymer‐metal interface by a scanning electron microscope (SEM).

接着継手の被着体表面粗さ形状が接着強度に及ぼす影響

The influence of adherend surface roughness on the failure at adhesive-adherend interface is analyzed experimentally for the adhesive joints of two types. Anisotropy of roughness undulation at adhesive-adherend interface produces the mechanical intertwining effect, and contributes to increase of shearing strength of adhesive bonding. The adherend surface roughness Ry' that minimizes the adhesive bonding strength is observed for simple lap joints. When the adherend surface roughness Ry is larger than Ry', it is general view that the larger the adherend surface roughness Ry is, the higher the bonding strength becomes. In the domain Ry < Ry' conversely, the strength of adhesive bonding extremely increases for small decrease of roughness. Randomly scratched adherend surface with minimum Ry shows high strength of adhesive bonding. Moreover, experimental analysis is carried out about strength characteristics of butt joints acted normal load for adhesive layer.

Torque Transmission Capabilities of Bonded Polygonal Lap Joints for Carbon Fiber Epoxy Composites

Abstract Although carbon fiber epoxy composite materials have excellent properties for structures, the joint in composite materials often reduces the efficiency of the composite structure because the joint is often the weakest area in the composite structure. In this paper, the effects of the adhesive thickness and the adherend surface roughness on the static and fatigue strengths of adhesively-bonded tubular polygonal lap joints have been investigated by experimental methods. The dependencies of the static and fatigue strengths on the stacking sequences of the composite adherends were observed. From the experimental investigations, it was found that the fatigue strength of the circular adhesively-bounded joints was quite dependent on the surface roughness of the adherends and that polygonal adhesively-bonded joints had better fatigue strength characteristics than circular adhesively-bonded joints.

Optimal tubular adhesive-bonded lap joint of the carbon fiber epoxy composite shaft

The effects of adhesive thickness and adherend surface roughness on the fatigue strength of the tubular adhesive-bonded single lap joint were experimentally investigated using small fatigue test specimens (φ21 mm) whose adherends were made of S45C carbon steel. From the fatigue experiments, it was found that the optimal arithmetic surface roughness of the adherends was about 2 μm and the optimal adhesive thickness was about 0·15 mm. Also, the manufacturing method of the adhesive-bonded tubular single lap joint was discussed for the reliable and optimal joint quality. Using the optimal adhesive thickness and the optimal adherend roughness, the prototype torsional adhesive joints for the power transmission shafts (φ66 mm) of an automotive or a small helicopter were manufactured and statically tested under torque. The tests were performed on the single lap joint, the single lap joint with scarf, the double lap joint, and the double lap joint with scarf. The one part of the adherend of the joint was made of high strength carbon fiber epoxy composite material and the other part of the adherend was made of S45C carbon steel. The stresses of joints were analyzed by the finite element method. In applying the finite element method to the composite adherends, the smeared laminate properties were used. From the experiments, it was found that the double lap joint was the best among the joints in terms of torque capacity as well as manufacturing cost.

Surface roughness effects on the stress analysis of adhesive joints

A finite element program was used to perform a parametric analysis of stresses generated by adherend surface roughness in lap and butt joints. Roughness asperities were idealized as having tip radius of curvature R1, height H1, and slopes A1. Failure criteria (maximum stress, yield, and fracture) were related to the geometric parameters by functions of the form: σ = σ o + cR rH hA a The specific material properties used for the analysis were those of tooth enamel and an orthodontic cement. Qualitatively however, these results are applicable to all structural adhesives.

Effect of bond angle on mixed-mode adhesive fracture

A maximum in mixed-mode adhesive fracture energy has been observed at bond angles of 45° using scarf-joint test specimens. It is shown here that by reducing the adherend surface roughness from 1.2μm CLA roughness (milled surfaces) to 0.08μm CLA roughness (polished surfaces) the fracture energy becomes a linear function of bond angle (no maximum at 45°) and there is an overall crease in fracture energy at all bond angles. These results are discussed in terms of crack initiation being “focused” into the interfacial region and a pinning of crack-tip shear displacements by the surface roughness of the milled adherends which does not occur for the polished adherends.