In this study a representative sandwich panel is investigated statically in two different configurations under similar bending loads. In one configuration serrations are introduced in the honeycomb core while the other one has un-modified core. Three-point bend test (TPBT) has been performed on both configurations through Finite Element Analysis (FEA) technique using ANSYS Workbench considering American Society for Testing and Materials (ASTM) standards. In both configurations the same aluminium honeycomb core is modelled having an adhesive layer in between adjacent foils to simulate actual scenario instead of relying on the block properties. Honeycomb core offers highest strength in its thickness (T) direction or the z-direction by virtue of its shape. Any distortion in the shape of the honeycomb adversely affects its strength. During bending the honeycomb core witnesses multidirectional forces consequently leading to distortion or crumpling. The serrations in the structure allow bending of the honeycomb core with minimal loss of strength by limiting the deformation to a specific region consequently preserving the shape as well as the strength of the honeycomb core. The results of both samples are compared with respect to deflection, strain and reaction force. It proves that serrated core is more favourable to be used in bent or curved sandwich panels.

The demands of modern materials are highly challenging as well as partially contradictory. For example, materials should be strong like steels but chemically inert like soft low-surface energy polymers. These conflicts can be overcome by effectively combining disparate materials in composites that allow fusing of the traditional material classes like ceramics, polymers, and metals. Such combinations require sufficient adhesion between the individual materials. If adhesion is based on mechanical interlocking, the chemistry and chemical compatibility of the individual materials play a negligible role for the adhesion, but the mechanical properties of the materials are exclusively important. This work focusses on a technologically relevant example of a micro-mechanical interlocking surface structure on grade 304 stainless steel (SST) by nanoscale sculpturing. Using a low aggressive/low toxic seawater-like and diluted HNO3-based electrolyte, the resulting structure is free from preferential grain-boundary etching. The sculptured surface is super hydrophilic with undercuts suitable for mechanical interlocking with polymers. In single-lap shear tests, different two-component adhesives failed cohesively on structured SST while showing more than a doubling of the ultimate shear strength compared to the state-of-the-art grit-blasted SST composites which only showed adhesive failure.

Advanced lightweight materials, including high-strength steels, aluminum, magnesium, plastics, and reinforced polymer composites, are increasingly used in industry. Combinations of mixed materials are becoming commonplace in the design of structures. Adhesives can be used to join a wide range and combinations of materials. However, joining of materials depends on their specific characteristics. The choice of adherend material is one particular and important parameter that influences adhesively bonded joint performance, and its effect should be taken into consideration in the design of adhesive joints. This article overviews experimental and modeling investigations on the influence of adherend properties on the strength of adhesively bonded joints.

Environment can impact the wear behavior of metals and alloys substantially. The tribological properties of Al0.6CoCrFeNi high-entropy alloys (HEAs) were investigated in ambient air, deionized water, simulated acid rain, and simulated seawater conditions at frequencies of 2–5 Hz. The as-cast alloy was composed of simple face-centered cubic and body-centered cubic phases. The wear rate of the as-cast HEA in the ambient air condition was significantly higher than that in the liquid environment. The wear resistance in seawater was superior to that in ambient air, deionized water, and acid rain. Both the friction coefficient and wear rate in seawater were the lowest due to the formation of oxidation film, lubrication, and corrosion action in solution. The dominant wear mechanism in the ambient air condition and deionized water was abrasive wear, delamination wear, and oxidative wear. By contrast, the wear mechanism in acid rain and seawater was mainly corrosion wear, adhesive wear, abrasive wear, and oxidative wear.

We present a specimen preparation procedure for atom-probe tomography using SemGlu from Kleindiek Nanotechnik, an adhesive that hardens under electron beam irradiation. The SemGlu adhesive is used in place of focused-ion-beam-induced deposition of organo-metallic Pt, W, or C to form a bond between the sample and the substrate during the specimen preparation procedure. We demonstrate the utility of this adhesive-based specimen preparation technique with a correlated atom-probe tomography-scanning transmission electron microscopy study of the iron-nickel alloy kamacite (ferrite, ɑ-iron) in the Bristol iron meteorite and two steel specimens.

Chip-package interaction (CPI) and the related thermomechanical stress in microchips increase the risk of failure in on-chip interconnect stacks, caused by delamination along Cu/dielectrics interfaces (adhesive failure) and fracture in dielectrics (cohesive failure). High-resolution transmission X-ray microscopy (TXM) is a unique technique to image crack propagation in on-chip interconnect stacks. The visualization of crack evolution in Cu/low-k Backend-of-Line (BEoL) structures is demonstrated using an experimental setup which combines high-resolution X-ray imaging with mechanical loading. The application of an indenter manipulator at the TXM beamline of the synchrotron radiation source BESSY II provides an unprecedented level of details on the fracture behavior of microchips. This in-situ experiment allows to identify the weakest layers and interfaces and to evaluate the robustness of the BEoL stack against CPI.

Bioinspired micromanipulators have been made based on gecko dynamic self-cleaning mechanism. Various particles such as spherical SiO2/polystyrene, and short fibrous glass can be captured, transmitted and dropped on glass substrate with precisely predesigned patterns, by using the micromanipulator with the help of atomic force microscope (AFM). It has been demonstrated that particle-pad interface and particle-substrate interface exhibit diverse adhesion behaviors under different z-piezo retracting speed. The particle-substrate adhesion increases faster than the particle-pad adhesion with increasing the detaching velocity, which makes it possible to manipulate the particles by adjusting the retreating speed only. Probability tests was performed to better choose suitable parameters for picking and dropping operations. This work provides a potential solution to manipulation of micro/nano particles for precise assembly.

A new waterborne acrylic (WAC) hybrid adhesive was evaluated for an untreated polypropylene lamination. The WAC hybrid adhesive was formulated with a new class of porous clay heterostructure (PCH), which was modified with 3-(trimethoxysilyl)propyl methacrylate (as a coupling agent) to promote chemical bonding with the acrylic matrix to form a methacrylate-functionalized PCH (MPCH). The WAC hybrid adhesive was based on copolymers (2-ethylhexyl acrylate, ethylene glycol methyl ether acrylate, 2-(hydroxyethyl) methacrylate, styrene and acrylic acid) with varying amounts of MPCH. The scanning electron microscopy micrographs revealed the presence of a well dispersed MPCH distributed throughout the matrix. The optimal adhesive performance, in terms of the 180° peel strength of bonded joints, of 140.2 N/m was achieved using 1.5 wt% of MPCH, while the thermal stability of the adhesives was improved with increasing MPCH loading levels.

An adhesive that can withstand elevated temperatures is necessary for the conservation of artifacts in hot climates. The use of Butvar B-98 as a modifier to raise the glass transition temperature of Paraloid B-72 was investigated. The characteristics of B-48N and B-72 blends, currently in use in the field of conservation, were used as a comparison for analysis of the B-98 and B-72 blends. Differential Scanning Calorimetry (DSC) was used to determine the glass transition temperatures (Tg) of the blends and shear testing was used to investigate the shear strength of the blends. While the B-98 and B-72 blends attained elevated glass transition temperatures and performed well during shear testing, issues regarding miscibility and phase separation of the blends were investigated using transmission FTIR, DSC, and optical microscopy.

The consolidating adhesive project is an international collaboration which aims to develop a new adhesive with well characterized physical, optical, and ageing characteristics specific for the consolidation of painted layers. Since starting in 2010, many findings have been made, and new useful polymer-tackifier, and polymer-tackifier-wax blends have been tested. The concept of component miscibility and the effect it has on the final properties of the adhesive is complex, but fundamental to the development of a new product. To quantify the properties conservators most need, the initial focus was on understanding BEVA® 371, a widely used poly(ethylene vinyl acetate) based heat-seal adhesive. It was originally developed as a lining adhesive for paintings, and has been adapted by conservators for a variety of consolidating applications; however, its ideal consolidation performance properties are starting to be out-weighed by concerns regarding its long-term stability, as well as recent formulation changes. There is a need for a new adhesive tailored to the requirements of the conservation field. This paper will discuss the results obtained thus far, and the goals for the future. The project is entering a new phase, where we hope to continue to explore new blends, and have conservator testing on painting mock-ups.

The self-assembly of known good dies (KGDs) on substrates using the liquid capillary method is shown to be a promising technology to achieve three-dimensional (3D) heterogeneous system integration and packaging. Firstly, the effects of the edge structures of self-assembled substrates and chips on alignment accuracies were investigated. When hydrophobic sidewalls with 10-µm-height steps were applied to both chips and assembly sites formed on substrates, the alignment accuracy within 1.0 µm was realized. The alignment accuracies were within 2.0 µm using either substrates or chips having 10-µm-height step structures with hydrophobic sidewalls. Self-assembly of 12-ch vertical-cavity surface-emitting lasers (VCSELs) with a long rectangle shape on glass substrates were also demonstrated. Separation of assembly sites into twelve areas enhanced the resultant force acting on the VCSEL short edge. The enhanced resultant force provided the high alignment accuracies within 2.0 μm. After the self-assembly of the VCSEL and the subsequent thermal compression, the chips successfully exhibited no degradation of their current–voltage (I–V) characteristics and appropriate 850-nm light emission. We demonstrated self-assembly and microbump bonding using non-conductive film (NCF)-covered dies with Cu/Sn microbumps for high-throughput and high-yield multichip-to-wafer 3D integration. The self-assembly of the NCF-covered dies provided high alignment accuracy within 1.1 μm on average. After the self-assembly of NCF-coved dies and thermal compression, microbump chains composed of 7396 bump joints were successfully obtained, resulting in good electrical properties of 32 mΩ/joint without any bridge shorts and failures. The variations of microbump joint resistance were maintained within 5% of the initial value after thermal cycle testing of even 1000 cycles.

The high-temperature performance of electronics packages was studied at 180°C, 200°C and 240°C for 3,000h. The structure tested consisted of a fairly large silicon chip attached with anisotropic conductive adhesive (ACA) onto an adhesiveless PI substrate. These structures showed good electrical reliability at 180°C. Several early failures were seen at the other temperatures. However, only 23% of the test samples failed at 200°C, while considerably more failures were seen at 240°C. The results showed that good high-temperature reliability can be achieved with polymer interconnections. However, the exposure time should be limited, especially at very high temperatures, to avoid failures caused by the materials becoming brittle.

The interface between the adhesive toes of geckos and a substrate consists of an array of regularly sized, densely packed, and elastically coupled nanoscopic contacts. The velocity-dependent friction exhibited by this system hints at a convolution of various material and structural effects. We explore the dynamics of frictional sliding in these materials using models based on arrays of coupled masses driven by external forces that can become pinned and unpinned to a potential energy landscape. The model system is driven at normalized velocities spanning 6 orders of magnitude, and the output of this model captures both the low-V and high-V behavior of the actual gecko materials. We explore modifications to the essential model that incorporate features more representative of the structure and behavior of the natural gecko system. These results have implications in the design of materials with custom frictional properties.

In this study, three hydrophobic polymers are investigated as potential adhesivesfor a shape memory polymer nerve cuff. At room temperature, the adhesivecandidate exhibited a maximum lap shear stress of 1.7251 MPa, compared to0.87641 MPa and 2.1815 MPa for two commercially available biocompatibleadhesives.

The aim of this experimental study is to investigate impact behaviors of the composite single-lap adhesive joints. The increasing impact energies, which are ranged from approximately 5 J to 30 J, are performed at the center of the composite plates having three different overlap lengths. It is shown that the overlap lengths and impact energy levels affect considerably the impact responses of the composite single lap joints. It is also shown that the bending stiffness of the composite increases by increase in the overlap length. An energy profiling method (EPM) is used to identify the penetration and perforation thresholds of composite lap joints. The damaged composite plates are visually inspected.

In this study, thiol-epoxy polymer composites are explored as candidates for high-temperature die attach applications. We present a polymer composite processing technique for die attach adhesives with low cure-stress. Lap shear samples of both a polymer adhesive and current industry adhesives were subjected to tensile testing and die shear strength was compared. At 260 °C, the candidate polymer adhesive exhibited a die shear strength of 0.500 MPa in comparison with 1.35 MPa and 0.258 MPa for two control adhesives. While samples showed less variation in properties in die shear strength between room temperature and 260 °C, the absolute die shear strength values were inferior to commercial adhesives at both room and elevated temperatures. We hypothesize that low cure stress networks, such as the thiol-epoxies presented, provide a compelling choice to engineer new die attach adhesives, but realize that further network refining is needed including the addition of adhesion promoters and other additives, a task better suited to industrial research with a focus in properties optimization.

The purpose of this study was to evaluate the ability of two dentin adhesive systems to induce remineralization in the bonded dentin interface after in vitro thermo-cycling. Dentin surfaces were treated with two different adhesive approaches: (1) 37% phosphoric acid (PA) plus an “etch-and-rinse” dentin adhesive (single bond, SB) (PA+SB) or (2) application of a “self-etch” dentin adhesive (Clearfil SE bond, SEB). Three groups were established: (i) 24 h or (ii) 3 m storage, and (iii) specimens submitted to thermal cycling (100,000 cy/5 and 55ºC). Atomic force microscopy imaging/nanoindentation, Raman spectroscopy/cluster analysis with dye-assisted confocal laser scanning microscopy (CLSM) evaluation and Masson’s trichrome staining assessments were implemented for characterization. Thermo-cycling increased nanohardness in PA+SB at the hybrid layer (HL) and in SEB at the bottom of the HL (BHL). Young’s modulus increased at both the HL and BHL in SEB and at the HL in PA+SB, after thermal stress. Cluster analysis demonstrated an augmentation of the mineral–matrix ratio in thermo-cycled specimens. CLSM showed a decrease of both micropermeability and nanoleakage after thermo-cycling in PA+SB, and were completely absent in SEB. Trichrome staining reflected a scarce demineralized front in PA+SB after thermo-cycling and total remineralization in SEB.

Nanoparticles of ∼55 nm in diameter have been found to significantly increase the fracture toughness of nanocomposites with a ductile polymer matrix. This paper presents a comparative study of the effectiveness of micrometer-sized and nanosized elastomeric particles in improving the fracture toughness and strength of polymeric adhesives. Particular focuses are on the effects of particle size, matrix ductility, and adhesive thickness on the shear strength and fracture toughness. The results reveal that for an epoxy adhesive cured with a J400 hardener, nanosized particles can produce nearly 18 times more increase in fracture toughness than what can be achieved using micrometer-sized particles at the same volume fraction of 5.0 vol%. This huge improvement of adhesives' fracture toughness by nanosized particles is similar to that observed in bulk nanocomposites, indicating that the superior toughening mechanism of nanosized elastomeric particles is equally effective in thin adhesives constrained by stiff adherends.

Organic composite materials can be readily found in our daily life, such as plywood used in construction industry and bamboo composites as indoor and outdoor flooring materials. These organic composite material systems consist of cellulose fibers bonded with each other through adhesives, leading to a bonded system with a gradient structure that possesses a unique structural behavior which has a great potential to be used as load-bearing building materials. In view of the manufacturing process of such composite material systems and the structure in-between the cellulose fibers and the adhesives, the interfacial adhesion of such systems at multiscale would play a major role in determining their capability in load-bearing structural applications. In this research work, the interface between cellulose fiber and phenol-formaldehyde adhesive is chosen as a representative of the organic composite material system and molecular dynamics simulation is used for quantifying their mechanical properties and the corresponding interfacial adhesion. Here we demonstrate that cellulose fiber has a strong affinity to a phenol-formaldehyde adhesive with an adhesion energy of 151.3 mJ/m2. To the best of our knowledge, this is the first study that reports this material property for cellulose-adhesive system, which is three times larger than that between the gecko foot’s hair and the mineral surface. The mechanism of such strong adhesion is due to the possible hydrogen bonding between the cellulose and the adhesive.

Nitric oxide (NO) release can promote healthy tissue regeneration. A PEG-fibrinogen adhesive hydrogel that would allow for inducible NO release was created with mechanical properties that could be tailored to specific applications and tissue types. PEG (4-arm)-fibrinogen hydrogels of varying ratios were derivatized with S-nitroso-N-acetyl-D, L-penicillamine (SNAP)-thiolactone to create an active NO donor material. Controlled release from gels was established using light as the activating source, although temperature, pH, and external mechanical loading are also means to induce active NO release. Gels with varying ratios of fibrinogen to PEG were made, derivatized, and tested. Gels below a ratio of 1.5:1 (fibrinogen:PEG) did not gel, while at ratio of 1.5:1 gelation occurs and NO release can be induced. Interestingly, the release from 1.5:1 gels was significantly lower compared to 2:1 and 3:1 gel formulations. Rheometric data show that lower ratio gels are more elastic than viscous. Derivatized gels exhibited linear elastic moduli, behaving more like other more synthetic hydrogels. Swelling data indicates that as the ratio of fibrinogen to PEG increases the swelling ratio decreases, likely due to the hydrophobic nature of the NO donor. Cells remain viable on both derivatized and non-derivatized gels.