Proportional method for evaluating intensity of singular stress field for butt joint with adhesive spew

In this paper, a proportional method for evaluating an intensity of singular stress field (ISSF) at an interface corner in a butt joint (BJ) with an adhesive spew is proposed. Square-shaped inclusion models under bi-axial tensile stress and under shear stress are used as reference models. The ISSFs for the BJ are calculated by superposing those for the reference models. The reference and BJ models are analyzed by FEM under the same mesh division and the same material combination, and the stresses applied to the reference models are determined by the FEM stresses at the interface corner. The validity of the present method is examined by applying to the BJ composed of the steel and the epoxy resin. The asymptotic solution obtained by the method is in agreement with the FEM stress distributions. Then, the ISSFs for the BJ are calculated by changing adhesive spew similarly. It is shown that the ISSF normalized by the adhesive thickness is constant independent of the thickness.

Characterization of an Experimental Two-Step Self-Etch Adhesive’s Bonding Performance and Resin-Dentin Interfacial Properties

This study evaluated an experimental two-step self-etch adhesive (BZF-29, BZF) by comparing it with a reference two-step self-etch adhesive (Clearfil Megabond 2, MB) and a universal adhesive (G-Premio Bond, GP) for microtensile bond strength (μTBS) and resin-dentin interfacial characteristics. Twenty-four human third molars were used for the μTBS test. Bonded peripheral dentin slices were separated to observe the resin-dentin interface and measure the adhesive layer thickness with SEM. μTBS data of the central beams were obtained after 24 h and 6 months of water storage. Fracture modes were determined using a stereomicroscope and SEM. Nine additional third molars were used to determine the elastic modulus (E) employing an ultra microhardness tester. Water storage did not affect μTBS of the tested adhesives (p > 0.05). μTBS of BZF and MB were similar but significantly higher than GP (p < 0.05). BZF achieved the highest adhesive layer thickness, while GP the lowest. E of BZF and MB were comparable but significantly lower than GP (p < 0.05). Except for GP, the predominant fracture mode was nonadhesive. The superior bonding performance of BZF and MB could be attributed to their better mechanical property and increased adhesive thickness imparting better stress relief at the interface.

Non-Monotonous Effect of Adhesive Thickness on The Dynamic Stiffness of Adhesive Butt Joint

This research investigated the effect of the thickness of adhesive to the stiffness (Young’s modulus) of adhesive butt joint at high strain rate loading. A split Hopkinson pressure bar (SHPB) test is used to obtain the stress-strain response of join specimen at strain rate of 530±10 s-1. The joint is composed of aluminum adherend bonded by epoxy adhesive with 0.5, 1, 2, and 3 millimeter of thickness variation. The results show that the joint deformed elastically and the stiffness increases with the increase of adhesive thickness. However, the rate at which the stiffness increases with thickness decreases at thick adhesive layer. The facts of this research are important for the improvement of the crashworthiness of structure such as automobile structures.

A review on composite patch repairs and the most important parameters affecting its efficiency and durability

In many industries, when replacement of a part is not possible or economic, the repair is done. One of the best methods for repairing metal and composite parts is using composite patches. Repairing with a composite patch is a widespread field to extend the service life of the cracked components. This technique is more structurally efficient with fewer damages on the structure than others. The bonded patch offers many advantages over a mechanically fastened doubler, which include improved fatigue behavior, reduced corrosion, and easy conformance to complex aerodynamic contours. In this article, advantages of the composite patch and its efficiency and durability are discussed, and the most important parameters (patch and adhesive thickness, patch separation, residual stress, patch length and width, etc.) affecting its performance are studied based on the latest available references.