Development of Co-cured Single-Lap Joints Reinforced with Graphene-Modified Epoxy Adhesives: Manufacturing, Mechanical Characterization, and Structure–Property Evaluation

Articular cartilage has a fundamental role in joint function. While much is known about its structure, organization and biomechanical properties, there is a very poor understanding of how articular chondrocytes develop during embryogenesis and acquire the unique ability to organize and maintain the articular tissue. Given that articular cartilage forms in close juxtaposition with the joint, here we review past studies on limb joint determination and morphogenesis and more recent studies on a number of factors thought to have roles in joint and epiphysis development. These factors include: the homeobox gene Barx-1; the bone morpho-genetic protein (BMP) family member GDF-5 the growth factors HGF and PTHrP; and the transcription factor ERG. We summarize current thinking on how these factors participate in joint development and how some of these factors may influence development and behavior of epiphyseal chondrocytes. We also describe pertinent recent studies from our laboratories on ERG and the newly-identified alternatively spliced variant C-l-1, and finally propose a sequela of events that may subtend the process of determination and emergence of articular chondrocytes during limb synovial joint development.

Mechanical characterization and validation of poly (methyl methacrylate)/multi walled carbon nanotube composite for the polycentric knee joint

This study explores the development of adhesive joints incorporating embedded resistive heating elements, fabricated using Multi-Material Additive Manufacturing. By embedding conductive circuits within the adherends, localized heating enables controlled curing of the adhesive, optimizing its mechanical properties according to the specific application. This study focused on modifying the stiffness of the adhesive in order to reduce edge effects in the joints and allow for better load distribution. The adherends were made of PLA, the resistive heating elements were fabricated using carbon black-filled conductive PLA, and an epoxy resin served as the adhesive. Thermal and mechanical characterizations were conducted, evaluating the effects of different curing temperatures on joint strength. The tensile strength for joints cured at 120 °C exhibited a 58% increase in maximum breaking force and a 144% increase in elongation at break compared to the joints cured at room temperature. These findings highlight the potential of AM-integrated resistive heating for precise adhesive curing, enabling the local tailoring of the adhesive stiffness in the overlap volume.

Mechanical characterization of a high elongation and high toughness epoxy adhesive

A new strategy for the reinforcement of paraffin-based fuels based on cellular structures: The armored grain — Mechanical characterization

Methodology for the mechanical characterisation of hyperelastic adhesives. Experimental validation on joints of different thicknesses

A novel hot-melt cyclic olefin-based adhesive was designed as a transparent, non-tacky film of amorphous thermoplastic with a unique polymer micro-structure. The aim of the present paper is to assess the mechanical properties of the 0.1 mm thick COP hot-melt adhesive film through adhesive characterizations tests. The glass transition temperature was determined using dynamic mechanical analysis (DMA). For mechanical characterization, bulk and thick adherend shear specimens were manufactured and tested at a quasi-static rate, where at least three specimens were used to calculate the average and standard deviation values. Tensile tests revealed the effects of molecular chain drawing and reorientation before the onset of strain hardening. Thick adherend shear specimens were used to retrieve shear properties. Fracture behaviour was assessed with the double cantilever beam (DCB) test and end-notched flexure (ENF) test, for characterization under modes I and II, respectively. To study the in-joint behaviour, single lap joints (SLJs) of aluminium and carbon fibre-reinforced polymer (CFRP) were manufactured and tested under different temperatures. Results showed a progressive interfacial failure following adhesive plasticization, allowing deformation prior to failure at 8 MPa. An adhesive failure mode was confirmed through scanning electron microscopy (SEM) analysis of aluminium SLJ. The adhesive exhibits tensile properties comparable to existing adhesives, while demonstrating enhanced lap shear strength and a distinctive failure mechanism. These characteristics suggest potential advantages in applications involving heat and pressure across automotive, electronics and structural bonding sectors.

The goal of the present research was to find reference surfaces that would interpolate the results of a vast test campaign, performed on several epoxy adhesives, varying numerous parameters, and estimate static failure load values of joints characterized by identical geometries, but different dimensions. Results obtained from static shear tests of single-lap and double-lap specimens were statistically processed using Student’s unilateral test with confidence level of 99%. A multivariate regression was then applied in order to obtain polynomial functions able to describe the interpolation surface. In order to test the validity of the model, failure loads were calculated for two geometrical configurations within the dimensional range used in the experimental test campaign. These values were compared with those obtained from additional experiments, relative to the same geometries. The comparison confirmed the reliability of the developed model. Tendencies that could be translated into geometries characterized by different dimensions of the tested joints were sought, thanks to the experimental data for as much as 4 adhesives and 2 adherends. Scale factors were calculated that allow, in initial design phases, to estimate realistic failure loads based on initial indications, limited to a single geometry used by producers of adhesives in mechanical characterization.

The scope of 3D printing is limited by its maximum printing area, necessitating joints for assembling larger structural elements. Natural fibers have been employed to reinforce printed materials, enhance their mechanical properties, and reduce polymer usage. However, the effects of these fibers on bonded joints, particularly in the context of continuous natural yarns, remain underexplored in the literature. This study investigates the mechanical behavior of 3D‐printed single‐lap joints (SLJ) with biocomposite adherends, using Fused Filament Fabrication (FFF). Continuous Jute Fiber Reinforced Polymer (JFRP) and Polylactic Acid (PLA) were used to fabricate the adherends. Mechanical characterization, including surface roughness analysis and single‐lap shear tests, was performed on PLA‐PLA, JFRP‐JFRP, JFRP‐steel, and JFRP‐wood joints. Results show that the addition of continuous jute fibers in mono‐material joints increased the failure load by 66.53% compared to neat PLA‐PLA joints, due to a 47.20% increase in surface roughness. Jute Fiber Reinforced Polymer‐wood joints demonstrated the best performance, achieving a failure load of 2543.76N, 56.85% higher than JFRP‐JFRP joints, indicating their potential for mixed‐material, sustainable structures. Analytical models were applied to assess the load distribution along the adhesive. Highlights Continuous natural yarn improves composite behavior, reducing brittle failure. Natural fibers enhance failure load and mode toughness of bonded joints. Jute yarn in joints raises SLJ failure load by 66.53%, enhancing contact area. Analyses of 3D‐printed parts with natural fibers bonded to wood and steel. Bi‐material joints show better results due to higher rigidity.

Hybrid sol–gel films were prepared via a simultaneous organic‐inorganic UV‐curing process using a diaryliodonium salt as a superacid photogenerator. In this single‐step procedure, an epoxy functionalized reactive resin mixed with a variable amount of either of two epoxy trialkoxysilane precursors was UV‐irradiated, causing both the initiation of epoxy ring‐opening copolymerization and the catalysis of trialkoxysilyl sol–gel reactions. The concomitant photo‐induced sol–gel process was found to have a significant effect on the two related propagation mechanisms in competition for the oxirane ring‐opening—the active chain‐end and the activated monomer mechanisms—as proved by a systematic examination of the hybrid material microstructure through 29Si and 13C solid‐state NMR spectroscopy. The effect of the oxo‐silica network generation on the epoxy reaction kinetics was also evaluated using real‐time Fourier transform infrared spectroscopy upon varying the epoxysilane structure and its concentration. Thermal and dynamic mechanical analyses were systematically performed on these hybrids, by studying thoroughly their structure–property interdependence. Other mechanical characterizations through tribological and scratch tests suggested that the present photopolymer–silica hybrid material provides a powerful tool to tailor mechanical property profiles. Copyright © 2010 Society of Chemical Industry

Structurally efficient isogrid booms, manufactured from rigidizable composite materials, are becoming an enabling technology for spacecraft structures because of their high packing efficiency. Selection of the materials used in the construction of rigidizable space structures is commonly driven by mechanical performance properties at elevated temperatures. Mechanical properties testing was performed on composite tow samples and on an isogrid boom at various temperatures. To characterize elevated temperature behavior, the isogrid booms, and its subelement composite tows were manufactured from ILC’s TP283E shape memory polymer (SMP) matrix resin and a carbon reinforcement. Both the flexural modulus and the tensile modulus of the composite tow samples were determined as a function of temperature. These values were compared to the calculated values for the composite based on rule of mixtures analysis. The predicted rule of mixtures composite modulus is used in ILC’s isogrid analytical code to predict the structural properties of the isogrid boom. A number of composite tow samples were fabricated by ILC and mechanically characterized by the Aerospace Corporation to gather independent performance data. An isogrid boom was fabricated by ILC and mechanically characterized at elevated temperatures by James Madison University (JMU). JMU tested this boom in tension, compression, and also performed preliminary creep testing at various temperatures. A similar isogrid boom was fabricated by ILC and tested by The Aerospace Corporation for composite CTE performance. This paper discusses the results of both the composite tow testing and the isogrid boom testing in preand post-packing conditions. A discussion of the correlation between the predicted values and the actual test values is also presented. Introduction NASA and DoD space missions in the near future will require much larger satellites, the sizes of which will be beyond the capabilities of current technologies. The types of Gossamer spacecraft that will be needed include antennas, solar arrays, sunshields, solar sails, and telescopes (Figs. 1-2). Some systems being considered are hundreds of meters in size to accomplish mission goals. Due to the increase in payload size required, innovative support structures, which can be packed into the faring of available launch vehicles, must be developed. In recent years, research and development work has been performed in this area. Of the available options, one of the most promising technological advancements is the rigidizable inflatable structure. A rigidizable inflatable structure is one that is fabricated on Earth, packed into the launch container, and inflated for deployment once on orbit. After deployment, the material is rigidized, or hardened, to form a stiff composite structure that no longer needs the inflation gas for support. This class of structures has unique benefits such as low packing volume, reduced mass, and in most cases, very high deployed structural efficiency. Several types of construction can be used in a rigidizable inflatable including monocoque, isogrid, IsoTruss, and truss-frame booms. Each composite structure can be fabricated into a varying geometric shapes utilizing any number of resin and fiber types. The fibrous reinforcement can be in tow or woven fabric form. In order to optimize the structure, the sizes of the tows and the weave styles of the fabrics can be varied. It is also possible to manufacture near-zero coefficient of thermal expansion (CTE) booms through the fiber and resin selection and by optimizing the volume fractions of each. However, key to all mechanical performance properties is the ability to fold and tightly pack the material. Member AIAA † Associate Fellow AIAA Undergraduate Research Assistant, Dept. of Int. Science and Tech. Associate Professor, Dept. of Int. Science and Tech. Senior Scientist, Materials Sciences Dept. Distinguished Scientist, Space Materials Lab Figure 2. ILC 3.2m Diameter TSU Hexapod Testbed Figure 1. 1⁄2 Scale Next Generation Space Telescope Sunshield

The applications for composite materials, especially in the automotive, chemical, petroleum and aeronautical industries, have been growing steadily in recent years due to their excellent properties, such as high specific mechanical properties and good corrosion resistance. Consequently, there has been a considerable increase in research toward the development of their structural properties, as well as the development of non-destructive inspection techniques for these materials. This paper aims to evaluate the characterisation of failure mechanisms that occur in fibreglass reinforced polymeric matrix composites when subjected to tensile and flexural loads. The acoustic emission signals of failure mechanisms, emitted at the moment of breaking of test samples, are analysed in the frequency domain by the Fourier transform technique (spectral analysis), and in the time-frequency domain by the wavelet transform. Both techniques are evaluated in terms of the characterisation of failure mechanisms, such as: transverse matrix cracking (resin cracking), fibre/matrix debonding and delamination. The results obtained attest the efficiency of both techniques and are an encouragement for publication.

Effects of adhesive systems on the mechanical and fire-reaction properties of wood veneer laminates

Impact resistance of composite to aluminum single lap joints reinforced with graphene doped nylon 6.6 nanofibers

The mechanical properties of a commercially available hot-melt adhesive (HMA) have been studied under different environmental and loading conditions. To date, disassembly analyses including triggering features, design parameters, and time have not been fully investigated in the literature. In this study, experimental parametric studies have been performed on single lap joints considering the geometric features of the joint and a combination of thermo-mechanical effects. Disassembly time has been assessed through experimental analysis, considering variations in geometry, the use of alternative heat sources and different load conditions. Use of a heat gun as the heat source was found to lead to the highest variation in disassembly time compared to a static climatic chamber (i.e., industrial oven). In relation to the joint geometry, the disassembly time was mostly affected by the overlap length rather than the type or thickness of the base material. The outcomes of this study will drive the design of adhesive joints in mechanical applications, providing design-for-disassembly guidelines for the development of reversible joints employing hot-melt adhesives.