Lap Shear Tests Research Articles

Depolymerised lignin oil: A promising building block towards thermoplasticity in polyurethanes

The use of lignin as building block in the preparation of lignin-based thermoplastics has been a great challenge for the scientific community. Indeed, both the heterogeneous branched structure and the high hydroxyl functionality of lignin favours crosslinking reactions leading to the formation of thermosetting chemical structures. Some attempts have been made to circumvent these limitations, although the approaches required labour-intensive and time-consuming modifications of lignin and used only a relatively low amount in the materials. To tackle this problem, the present work employs lignin hydrogenolysis oil (LHO) which contains a low hydroxyl functionality oligomeric fraction suitable for the synthesis of thermoplastic polyurethanes (TPUs) via a two-step polymerization process. A series of TPUs were synthesized to investigate the impact of lignin content as well as soft segment molar mass on the chemical and thermo-mechanical properties of the materials. The study demonstrates that the use of high lignin content (38–46 wt. %) and high molar mass of the polyol (polypropylene glycol, PPG, Mn=4 kg mol−1) enhanced the mechanical properties of the obtained TPUs compared to counterpart polymers synthesized with lower molar mass of PPG. Additionally, LHO-based TPUs were applied as hot-melt adhesives for wood and their bonding strengths were evaluated by single lap shear tests. The lap shear adhesiveness was found to increase with increasing LHO concentration and decreasing molar mass of PPG. The developed methodology could lead to the preparation of robust thermoplastic lignin-based polyurethanes with a wide range of desired properties.

Laser transmission welding of polycarbonate sheets using electrolytic iron powder absorber

This paper presents Laser Transmission Welding (LTW) of polycarbonate sheets using electrolytic iron powder as an absorber to obtain a clean and high-strength joint without any gap between the sheets. Surface temperature is measured to analyze the bubble morphology and relate them with the heat absorbed at the interface. The lap shear test is performed to evaluate the weld strength, and fracture modes of the welded joints. The results show that maximum weld strength is achieved with smaller bubbles. Scanning electron microscope (SEM) micrograph of the fractured surface shows micro-fibrils at the inter-bubble space, enhancing the weld strength. The iron particles present inside the bubble increase the size of the bubbles, and the presence of cleavage facets reveals the brittle failure of the joint. The weld joints are fractured mainly by interfacial and substrate fractures. The optimum process parameters are obtained using a genetic algorithm (GA), and the confirmation test shows an improvement of 36.32 % in weld strength compared with Taguchi parameters.

Mechanism of bonding during laser transmission welding using EIP absorber

ABSTRACT This paper aims to investigate the bonding mechanism during laser transmission welding of polycarbonate sheets using an electrolytic iron powder (EIP) absorber. The experiments are performed at different scan speeds and laser powers. The mechanical strength is determined by the lap shear test. The influence of line energy, interface temperature, and absorptivity on weld strength is discussed. The weld characteristics, bond morphology, and elemental distribution at the cross-section and fracture interface of the welded samples are analyzed. The results show that the maximum breaking strength of 1180 N is obtained at the 400 mm/min scan speed and 100 W laser power. The iron particles are observed mechanically interlocked at the lowest line energy with partial chemical bonding. However, the chain diffusion and chemical bonding have been increased with line energy. Thermal degradation and burning of the polycarbonate at the interface restrict the bonding and reduces the weld strength.

Effect of diffusion bonding time on microstructure and mechanical properties of dissimilar Ti6Al4V titanium alloy and AISI 304 austenitic stainless steel joints

Abstract The main objective of this investigation is to study the effect of diffusion bonding time on microstructure and mechanical properties of dissimilar Ti6Al4V titanium alloy and AISI 304 austenitic stainless steel joints. The dissimilar joints of Ti6Al4V titanium alloy and AISI 304 steel were developed using the different levels of bonding time (30, 45, 60, 75 and 90 min) in a vacuum chamber at a bonding temperature of 900 °C and compressive pressure of 14 MPa. The microstructure of joints was analyzed using optical microscopy (OM) and scanning electron microscopy (SEM). The elemental analysis of joint interface was studied using the SEM energy dispersive spectroscopy (EDS). The evolution of intermetallic compounds at the joint interface was analyzed using X-ray diffraction (XRD). The ram tensile tests and lap shear tests were performed to assess the bonding strength and lap shear strength of dissimilar joints. Results showed that the dissimilar joints of Ti6Al4V alloy–AISI 304 steel developed using the diffusion bonding time of 75 min showed higher lap shear strength of 151 MPa and bonding strength of 244 MPa due to the better coalescence of the joining surfaces and evolution of optimum width of diffusion region having minimum embrittlement effects.

Mechanoluminescent Visualization of Crack Propagation for Joint Evaluation.

In this study, methods for the mechanoluminescent (ML) visualization of crack propagation and mechanical behavior to evaluate adhesive joints are demonstrated and explained. The first step involved sample preparation; an air spray was used to apply ML paint to the surface of the adhesive joint specimens. The performance of the ML sensor was described to examine the measurement conditions. The results of ML sensing during a double cantilever beam (DCB) test and a lap-shear (LS) test are demonstrated as these are the most frequently and widely used methods for evaluating adhesives. Originally, it was difficult to directly quantify the crack tip and strain/stress distribution and concentration because the crack tip was too small, and the effects of the strain could not be observed. The mechanoluminescence, crack propagation, and mechanical behavior during mechanical testing can be visualized via the ML pattern during the adhesive evaluation. This allows for the recognition of the precise position of the crack tips and other mechanical behaviors related to structural failure.

Adhesive and biodegradable polymer mixture composed of high -biosafety pharmaceutical excipients as non-setting periodontal dressing.

Periodontal dressing is a surgical dressing applied to oral wounds after periodontal surgery. Currently, all commercially available setting periodontal dressings are stiff, uncomfortable, with poor aesthetics, and need to be removed at the patient's follow-up visit, which may cause secondary damage. A periodontal dressing with soft texture, biodegradable properties, and that could balance both comfort and aesthetics is urgently desired. Hence, non-setting and degradable dressings were developed using sodium carboxymethyl cellulose, Eudragit S 100 and povidone K30, which were compared with the commercial degradable dressing Reso-pac®. The mucosal adhesion of the dressings was evaluated by lap shear tests, which indicated adequate adhesion. The in vitro swelling rates of the dressings were approximately half that of Reso-pac®, which led to less saliva adsorption and better dimensional stability. The dressings also exhibited satisfactory biocompatibility according to the results of CCK-8, Live/Dead staining, hemolysis, and subcutaneous implantation assays. Moreover, the dressing promoted the healing of full-thickness mucosal wounds in the palatal gingivae of SD rats and contributed to better therapeutic effect than Reso-pac®. Considering the multiple advantages and the pure pharmaceutical excipient formula, we anticipate that this dressing could be a promising product and may enter clinical practice in the near future.

Influence of Maleinized Polybutadiene on Adhesive Strength and Toughness of Epoxy Resins

This study explored the effect of maleinized polybutadiene (MPB) on the mechanical properties of epoxy resins. Diglycidyl ether of bisphenol-A, an epoxy resin, was modified by incorporating MPB having different molecular weights in order to improve the fracture toughness and peel strength. MPB was mixed with epoxy resin at several concentrations (5, 10, and 15 phr), with the epoxy resin as the major phase and MPB as the minor phase. A comparative study was performed to investigate the influence of MPB on epoxy resins based on their molecular weight difference. Lap shear test results showed that the shear strength of the MPB-modified epoxy resins was superior to that of the neat epoxy resin. At 10 wt% MPB loading, the modified epoxy resin exhibited an 87% enhancement in T-peel strength relative to that of the neat epoxy resin. Moreover, the fracture energy of the modified epoxy system increased proportionally with the amount of MPB in the epoxy matrix. These results indicate that MPB incorporation is a simple and effective method for designing multifunctional epoxy resins, thus facilitating their industrial application in various spheres.

Preparation and Properties of Polydopamine Coated Modified Calcium Alginate/Polyacrylamide Anti-adhesive Hydrogel

Film and hydrogel materials are mainly used as anti-adhesion barriers to prevent intrauterine adhesions (IUA) after surgery, but the efficacy of materials currently used in clinical practice is still not satisfactory due to insufficient adhesion and rapid degradation. Calcium alginate/polyacrylamide (CA/PAM) double-network hydrogel has excellent mechanical properties and biocompatibility, which is suitable for anti- adhesion materials, but the adhesion is insufficient and easy to shift. In this paper, polydopamine (PDA) coating was used to modify the CA/PAM hydrogel, and PDA@CA/PAM hydrogel was prepared to improve its adhesion properties. The SEM images show that the PDA coating is successfully applied, and that the hydrogel has a good three-dimensional porous network structure. The mechanical property test showed that the hydrogel had excellent tensile and compressibility, which allowed it to enter the target location smoothly and withstand certain pressure. The lap-shear test demonstrated that the modification of PDA coating significantly improved the tissue adhesion properties of CA/PAM hydrogels. The swelling and degradation properties indicated that the hydrogel could absorb the wound exudate and keep it on the wound for a certain period of time. The introduction of PDA coating also improved the hydrophilicity of the hydrogel. Cytotoxicity tests and hemolysis experiments showed that the cell activity of hydrogel was above 80%, and the hemolysis rate was below 5%. Moreover, PDA@CA/PAM hydrogel showed higher cell compatibility and blood compatibility than that of CA/PAM.

Ultrasonic Welding of Additively Manufactured PEEK and Carbon-Fiber-Reinforced PEEK with Integrated Energy Directors

The thermoplastic polymer polyether ether ketone (PEEK) offers thermal and mechanical properties comparable to thermosetting polymers, while also being thermally re-processable and recyclable as well as compatible with fused filament fabrication (FFF). In this study, the feasibility of joining additively manufactured PEEK in pure and short carbon-fiber-reinforced form (CF-PEEK) is investigated. Coupon-level samples for both materials were fabricated using FFF with tailored integrated welding surfaces in the form of two different energy director (ED) shapes and joined through ultrasonic polymer welding. Using an energy-driven joining process, the two materials were systematically investigated with different welding parameters, such as welding force, oscillation amplitude and welding power, against the resulting weld quality. The strengths of the welded bonds were characterized using lap-shear tests and benchmarked against the monotonic properties of single 3D-printed samples, yielding ultimate lap-shear forces of 2.17kN and 1.97kN and tensile strengths of 3.24MPa and 3.79MPa for PEEK and CF-PEEK, respectively. The weld surfaces were microscopically imaged to characterize the failure behaviors of joints welded using different welding parameters. Samples welded with optimized welding parameters exhibited failures outside the welded region, indicating a higher weld-strength compared to that of the bulk. This study lays the foundation for using ultrasonic welding as a glue-free method to join 3D-printed high-performance thermoplastics to manufacture large load-bearing, as well as non-load-bearing, structures, while minimizing the time and cost limitations of FFF as a fabrication process.

The Mechanical Behavior and Enhancement Mechanism of Short Carbon Fiber Reinforced AFS Interface

The aluminum foam sandwich (AFS), which perfectly combines the excellent merits of an aluminum foam core and face sheet materials, has extensive and reliable applications in many fields, such as aerospace, military equipment, transportation, and so on. Adhesive bonding is one of the most widely used methods to produce AFS due to its general applicability, simple process, and low cost, however, the bonding interface is known as the weak link and may cause a serious accident. To overcome the shortcomings of a bonded AFS interface, short carbon fiber as a reinforcement phase was introduced to epoxy resin to reinforce the interface adhesion strength of AFS. Single lap shear tests and three-point bending tests were conducted to study the mechanical behavior of the reinforced interface and AFS, respectively. The failure mechanism was studied through a macro- and microanalysis. The result showed that after the reinforcement of carbon fiber, the tangential shear strength of the interface increased by 73.65%. The effective displacement of AFS prepared by the reinforced epoxy resin is 125.95% more than the AFS prepared by the unreinforced epoxy resin. The flexure behavior of the reinforced AFS can be compared with AFS made through a metallurgical method. Three categories of reinforcement mechanisms were discovered: (a) the pull off and pull mechanism: when the modified carbon fiber performed as the bridge, the bonding strength improved because of the pull off and pull out of fibers; (b) adhesion effect: the carbon fiber gathered in the hole edge resulted in epoxy resins being gathered in there too, which increased the effective bonding area of the interface; (c) mechanical self-locking effect: the carbon fiber enhanced the adhesive filling performance of aluminum foam holes, which improved the mechanical self-locking effect of the bonding interface.

Effect of primer and sealant in refill friction stir spot welded joints on strength and fatigue behaviour of aluminium alloys

The refill friction stir spot welding (RFSSW) is one of the promising friction stir welding (FSW) methods consisting in the joint creation by plunging and retracting the rotating tool into the overlapped sheets without an exit hole after welding.This work aims to fulfil a knowledge gap related to use of aluminium semi-products in a final configuration state (including anodizing, primer and sealant application) for RFSSW process by means of the lap-shear and cross-tension mechanical test, fatigue performance, metallographic and fractographic analyses, and digital image correlation (DIC) technique. Sheet semi-products of thicknesses from 2 to 3 mm made of AA7050-T7451 and AA2024-T3 aluminium alloys in bare and/or anodised condition were used for the lap-joint specimens manufacturing and five various material joint combinations were analysed.The effect on static strength for the joint configurations with primer and sealant was studied and compared with the bare materials’ RFSSW joints. Fatigue tests showed that the primed configurations exhibited a higher scatter of the results and a different slope of fatigue curve with a higher fatigue limit value as compared with the bare material’s joints exhibiting a higher ultimate static strength.

Applicability of ultrasonic welding to Ag-stabilized REBCO CC joints and evaluation of their electromechanical properties

Manufacturing a single long-length rare-earth barium copper oxide (REBCO) coated conductor (CC) tape with uniform critical current (I c) is still a challenge; therefore, joining between multiple-length CC tapes is needed in the production of longer CC tapes for superconducting cables, coils, and magnets. Various joining techniques have been developed to achieve acceptably low joint resistance (R j) with no I c degradation and good electromechanical properties. The authors established ultrasonic welding (UW) and hybrid welding (HW) methods for joining Cu-stabilized CC tapes with different configurations. However, these methods have yet to be applied to Ag-stabilized CC tapes to produce compact joints and longer tapes during in-line production. This study used the UW and HW methods to fabricate Ag-stabilized CC joints to have low R j without I c degradation through a direct connection at the overlapped Ag layers between both CC tapes. Two CC tape samples with different thicknesses of ∼2 µm and ∼6 µm Ag stabilizers were supplied to produce UW and HW Ag-stabilized CC joints. These were compared with soldered CC joints fabricated by a mechanically controlled soldering method. In the case of UW, the design of experiment using the Taguchi method was used to systematically determine the optimized weld parameter combination that yields a lower R j without any I c degradation. This study is a systematic attempt to evaluate the applicability of UW for solid-state joining between thin Ag layers, unlike the conventional joining of thick Cu stabilizers. Moreover, the electromechanical properties of differently processed Ag-stabilized REBCO CC joints were evaluated using both lap-shear and double-bending tests. As a result, the optimum UW parameter combinations were obtained to achieve Ag-stabilized CC joints. However, some variations were probably due to the differences in the production batch and thickness of the Ag layers. The UW Ag-stabilized CC joints showed superior joint characteristics and electromechanical properties compared to soldered CC joints. Good solid-state bonding of the Ag layers was observed through microscopic observation of the cross-section at the joint region of the UW CC joint. The joint characteristics and electromechanical properties of the UW Ag-stabilized CC joints can be further improved using the HW method.

Experimental investigation on debonding behavior of Fe-SMA-to-steel joints

This work is the first systematic study on the static behavior of adhesively-bonded Fe-SMA-to-steel joints in applications adopting iron-based Shape Memory Alloys (SMAs). In order to provide a better understanding on the mechanical behavior of the adhesively bonded joint, an experimental campaign was established, involving 24 lap-shear tests in a displacement-controlled loading regime. The test series includes two types of Fe-SMAs (non-prestrained and prestrained), three types of adhesives (SikaDur 30, Araldite 2015, and SikaPower 1277), and three different thickness values (0.5, 1, and 2 mm) for the adhesive. A digital image correlation (DIC) technique was employed to measure the full-field displacement and strain, which were then used to infer the shear behavior. The mechanical behavior was analyzed on the basis of the experimentally derived load–displacement curves, the shear stress profiles along the bond line, and the bond–slip curves; three stages were observed during the loading process of a bonded joint: (i) a linear stage, (ii) a damage accumulation stage, and (iii) a debonding propagation stage. The test results indicate that a more ductile adhesive or a thicker adhesive layer possess a higher fracture energy, leading to a greater bond capacity. The results were also compared against those from lap-shear tests on carbon fiber reinforced polymer (CFRP) bonded joints. It is found that an Fe-SMA bond and a CFRP bond behave similarly when a linear adhesive is utilized; a nonlinear adhesive, however, results in significant mechanical differences between the two bonded joints, which merit individual analysis.

On the feasibility of joining additively-manufactured 316L stainless steel and poly-ether-ether-ketone by ultrasonic energy

• The joining of additively manufactured metal-polymer parts via U-Joining was proven. • Through-the-thickness reinforcements improved the joint mechanical performance. • Ultimate lap-shear forces up to 3.2 ± 0.2 kN were achieved by the produced joints. • Polymer penetrated metal surface cavities, improving micromechanical interlocking. • Fractography analyses showed a mixture of cohesive and adhesive failure. Ultrasonic Joining (U-Joining) process is a friction-based joining technique capable of producing through-the-thickness reinforced (TTR) hybrid joints between surface-structured metals and unreinforced or fiber-reinforced thermoplastics. Previously, the process feasibility has been demonstrated to join injection-molded Ti-6Al-4V and extruded unreinforced and laminated glass-fiber-reinforced polyetherimide structures, resulting in joints with improved out-of-plane strength and fatigue performance. However, there is an unexplored field concerning the joinability of additively manufactured (AM) metal and polymer parts via U-Joining. AM allows the production of structures with complex designs, but joining AM parts can represent a challenge as defects might appear along the process, such as delamination. In this work, the feasibility of joining laser powder bed fusion (LPBF) 316L stainless steel and fused filament fabricated (FFF) poly-ether-ether-ketone (PEEK) via U-Joining is demonstrated. Optical and scanning electron microscopy showed that TTRs were fully inserted into the polymer and that molten PEEK could flow around and penetrate metal surface cavities, thereby improving the macro- and micromechanical interlocking between the parts. Finally, quasi-static lap shear tests were performed, showing an improvement in the ultimate lap shear force up to 2.8 times (from 1.1 ± 0.2 kN to 3.2 ± 0.2 kN) and the displacement at break up to 2.1 times (from 0.7 ± 0.1 mm to 1.45 ± 0.2 mm) when compared to unreinforced (flat pinless) reference joints produced with the same energy input.

Study on the SPCC and CFRTP Hybrid Joint Performance Produced with Additional Nylon-6 Interlayer by Ultrasonic Plastic Welding

Due to the high degree of dissimilarity in physicochemical properties between metal and carbon fiber, it presents a tremendous challenge to join them directly. In this paper, cold rolled steel (SPCC) and carbon fiber reinforced thermoplastic (CFRTP) chopped sheet hybrid joints were produced with the addition of Nylon 6 (PA6) thermoplastic film as an intermediate layer by the ultrasonic plastic welding method. The effect of ultrasonic welding energy and preheating temperature on the hybrid joint microstructure and mechanical behavior was well investigated. The suitable joining parameters could obtain a strong joint by adding the PA6 film as an intermediate layer between the SPCC and bare carbon fibers. Microstructural analysis revealed that the interface joining condition between the PA6 film and the SPCC component is the primary reason for the joint strength. The crevices generated at the interface were eliminated when the preheating temperature arrived at 200 °C, and the joint strength thus significantly increased. The lap shear test results under quasi-static loading showed that the welding energy and preheating temperature synergistically affect the joint performances. At 240 °C, the joint strength value reached the maximum. Through the analysis of the microstructure morphology, mechanical performance, and the failure mechanism of the joint, the optimized joining process window for ultrasonic plastic welding of SPCC-CFRTP by adding an intermediate layer, was obtained.

Surface degradation assisted welding for vitrimer composites

Composites employing vitrimer (referred to as dynamic covalent network polymer) matrix can be directly welded thanks to bond re-association. Strong welding of vitrimer composite is anticipated to fabricate complex composite structures but remains challenging. Here, surface degradation is introduced to assist in welding carbon-fabric-reinforced epoxy vitrimer composites. The composites are immersed in ethylene glycol for a controlled degradation time before welding. We call it controlled surface degradation. The chemical and physical properties of the degraded surface are measured to reveal the effects of degradation on welding. The welding strengths with various welding pressure and time are studied by single lap-shear tests. Comparing with previously direct welding, the presented surface degradation assisted welding highly increases the welding strength, while significantly lowers the welding pressure.

Promoting Silk Fibroin Adhesion to Stainless Steel Surfaces by Interface Tailoring.

Bonding dissimilar materials has been a persistent challenge for decades. This paper presents a method to modify a stainless steel surface (316 L), routinely used in medical applications to enable the significant adhesion of a biopolymer (silk fibroin). The metallic surface was first covalently grafting with polyacrylamide, to enable a hydrogen bonding compatible surface. The polymerisation was initiated via the irreversible electrochemical reduction of a 4-nitrobenzene diazonium salt (20 mM), in the presence of an acrylamide monomer (1 M) at progressively faster scan rates (0.01 V/s to 1 V/s). Examination of the modified samples by FT-IR was consistent with successful surface modification, via observations of the acrylamide carbonyl (1600-1650 cm-1 ) was observed, with more intense peaks correlating to slower scan rates. Similar observations were made with respect to increasing surface polarity, assessed by water contact angle. Reductions of >60° were observed for the grafted surfaces, relative to the unmodified control materials, indicating a surface able to undergo significant hydrogen bonding. The adhesion of silk to the metallic surface was quantified using a lap shear test, effectively using silk fibroin as an adhesive. Adhesion improvements of 5-7-fold, from 4.1 MPa to 29.3 MPa per gram of silk fibroin, were observed for the treated samples, highlighting the beneficial effect of this surface treatment. The methods developed in this work can be transferred to any metallic (or conductive) surface and can be tailored to complement any desired interface.

Evaluation of the cracked lap shear test for mixed-mode fracture toughness estimation of adhesive joints

Cohesive zone models are a widely used method in adhesive joint strength predictions, but it requires the knowledge of fracture toughness of the adhesive in the different loading modes, together with the mixed-mode behaviour. The cracked lap shear test is a simple but seldom studied mixed-mode test and, as such, a deeper knowledge about its accuracy and of the available data reduction methods is required. This work consists of the experimental and numerical analysis of the cracked lap shear test to estimate the mixed-mode fracture toughness of two structural adhesives. The experimental work consisted of testing cracked lap shear specimens with the different adhesives. Numerically, cohesive zone model were used to predict the behaviour of bonded joints under mixed mode, while assessing the validity of the available data reduction methods to estimate fracture toughness. While the experimental analysis showed that the Brussat’s method led to offset results compared to the other methods, the cohesive zone model analysis confirmed the inadequacy of the Brussat's method, and the suitability of the Grady and Kinloch's models for mixed-mode fracture analysis.

Insights into the micromechanical response of adhesive joint with stochastic surface micro-roughness

Micro-roughness at adhesion surface yields significant influences on the structural behaviour of adhesive joints. Investigations into the micromechanical mechanism are extremely limited. This works developed a novel particle-based model of joints with stochastic microstructural features of roughness, which can capture refined multi-scale responses as first of this kind. Aluminium adherends with mechanical surface treatments were firstly scanned using 3D laser scanning microscope. The statistical features and reconstruction method of micro-roughness profiles were determined. Single lap shear tests on joints made of epoxy adhesive (Loctite EA 9497) and treated aluminium adherends were performed to provide testing data and observations on failure modes. The refined numerical models were subsequently developed to examine the influences of the actual micro-roughness on the micromechanical behaviors and failure mechanism. The mechanical interlocking, mitigation on crack propagation due to the irregular roughness were investigated. It is followed by introducing the reconstructed roughness of various magnitudes and further numerically examining the micromechanical responses by key stochastic parameters such as root mean square roughness and correlation length. The results indicate that the mechanical interlocking contribute more to enhancing the joint strength than the increase of adhesion area by micro-roughness. A rougher surface in either horizontal or vertical directions does not exhibit a consistent improvement of joint strength, which also depends on the threshold of roughness and the surface skewness triggering the transition of failure modes.

Surface roughness – the key for roll bonding aluminium

In this study, the commercially pure aluminium is roll bonded at ambient temperatures. The effect of surface roughness and roll speed on the bond strength is evaluated by using the lap shear test. It is observed that the bond strength increased considerably with increasing surface roughness. The deformation caused owing to scratch brushing changed the surface roughness profile, which is the salient reason for the bond strength variation. Continuous striations with peaks and valleys of small-scale heights are observed at lower roughness values. Increasing roughness has reformed them into discrete profile asperities with sharp tips, influencing localised junction formation. On the other hand, the roll velocity has shown hardly any effect on the roll bonding of aluminium. With thorough investigation, it was conclusively explained that the effective change in the bond strength was not appreciable with varying the roll speed, provided the roll bonding takes place at optimised surface roughness conditions.