Lap Shear Strength Of Joints Research Articles

The Effect of Immersion on the Breaking Force and Failure Locus in an Epoxy/Mild Steel System

Abstract This paper presents the effects of immersion on the adhesion behavior in a polyamide-cured epoxy system immersed in sodium chloride electrolyte adjusted to three different pH values. The strength of lap shear joints was measured before and after exposure and after redrying. The failure locus was determined on a macroscopic and microscopic level. It was found that a large adhesion loss occurred upon immersion. Most of that loss was recovered upon redrying. All of the breaking force was recovered when the immersion fluid was distilled water. The locus of failure was primarily through the bulk of the adhesive before immersion. After immersion the failure was interfacial with a thin residue of polymer remaining on the metal surface. These results are discussed with respect to earlier work on the water absorption properties of the system.

A method of determining the surface acidity of polymeric and metallic materials and its application to lap shear adhesion

A method has been developed to measure the surface acidity of solids using the contact angles of seven probe liquids. The geometric mean model was used to calculate the surface free energy. Then the value of the solid polarity, from the geometric mean, was compared with the polarity values calculated using the geometric mean dispersive component and the contact angles of two Lewis acids (liquefied phenol and glycerol) and two Lewis bases (formamide and aniline.) The deviation between these values was used to determine a value for the acidity, referred to as D. D was measured for a series of polymeric and metallic materials. Lap shear joints were fabricated and tested using these substrates and two adhesives, a urethane and an epoxy. The acidity of the substrate surfaces was found to affect the lap shear joint strength.

Chemical interaction in the system aluminum oxide-primer-adhesive

In the present work chemical interactions between sealed chromic-acid-anodized or conversion-coated Al1100, two proprietary primers and PR-420, a polyurethane adhesive, were studied. The chemical compositions of the primers and the adhesive were determined. All the relevant combinations of substrate-primer-adhesive were evaluated, using FTIR, Auger and SIMS spectroscopies. Single lap joint shear strength of the various combinations served as an indicator to the preferred surface treatment for a sound adhesive bonding. Chromic acid anodizing with a commercial AD-6 primer gave the best results. Correlation between chemical interaction and bond strength was observed.

Effects of symmetrical bonding defects on tensile shear strength of lap joints having ductile adhesives

AbstractIn this paper we examine the effect on joint strength of depleting the bond line of a relatively flexible adhesive (polyethylene) while maintaining a constant adhesive film thickness. It is shown that the tensile shear strength of a lap specimen is not governed by edge effects but rather by the bonded area. By using limit analysis of the plasticity theory, we demonstrate why the tensile shear strength of the joint is insensitive to stress concentrations at the bonding defects.

Ultrasonic welding of thermoplastics: Maher, A.D. and Walkin, P.British Plastics, 38, No. 7, 436 (1965)

Ultrasonic welding (UW) is not only a well-known industrial process but it has also been an active research area. Materials ranging from metals to non-metals e.g. polymers and from virgin materials to non-virgin materials e.g. composites are easily welded using this welding technique. Some research has already been carried out but more thorough analysis is needed on ultrasonic welding of thermoplastics. Two thermoplastics selected for this research are commercially known as Acrylo-nitrile-Butadiene Styrene (ABS) and Polypropylene (PP). ABS belongs to amorphous type of thermoplastic, whereas PP is semi-crystalline thermoplastic. Owing to this dissimilarity in their molecular structure, ultrasonic welding of these two plastics has already been considered to be different. Energy director (ED) is usually protruded on anyone of the samples to be welded. Ultrasonic energy is uniformly driven in the presence of energy director at a localized area between the samples. In this research, triangular (TRI) and semi-circular (SEMI) energy directors (ED) were protruded on the surface of specimen by designing and manufacturing injection molds. Tensile testing in shear was performed for measuring lap shear strength of joints after being welded ultrasonically at constant strain rate of 3.24 mm/minute. Maximum LSS (lap shear strength) of 17 MPa and 6 MPa were found for ABS with TRI ED and PP with SEMI ED respectively. In other words, these LSSs (lap shear strengths) were 34% and 14.63% of base material strength for ABS and PP respectively. In this work, a statistical analysis (General Linear Model) was also used to deduce meaningful information from experimentation for both materials. For different factor settings, percent change in LSS was also calculated. Maximum percent change in LSS was found for weld time e.g. 2682 and 76.67 from low to high level was computed for ABS and PP respectively. Similarly, 55 & 47.2 for amplitude and 41 & 6 for static force were calculated with ABS & PP respectively. Percent change in LSS of 409 and 47 was also evaluated from SEMI to TRI and TRI to SEMI EDs for ABS and PP respectively. All the factors appeared to be significant to affect the LSS but weld time was found to be the most significant to achieve the higher bond strength. After doing the GLM (General Linear Model) analysis, some interesting results were also highlighted. Experimental techniques were used to investigate the main reasons for these findings. Difference in softening temperatures, viscosities, temperature spreads, ED collapses, heat affected zones (HAZ) and fractured surfaces for both materials were used to determine the reasons for interesting effects. For example, low static force was required for ABS in gaining higher LSS due to its lower softening temperature and viscosity drop at weld zone. Thus this work presented new and deeper understanding of the ultrasonic welding of thermoplastics. Various hypotheses were also made after having gone through the literature. Experimental tools were also used to test these hypotheses. These technical tools included differential scanning calorimeter (DSC), melt flow index (MFI) tests, finite element analysis (FEA), high speed video camera (HSVC) and microscopy (optical and scanning electron). These tools helped approve or disapprove the hypotheses. Viscoelastic heating was considered to be crucial mechanism in joining thermoplastics ultrasonically. Viscoelastic heating was depending mainly upon loss modulus, applied frequency and strain amplitude. Weld strength further depended upon the temperature development at weld interface. Apart from above description, simulation based on FEA was also validated for its accuracy and precision. A good match was found between experimental and simulated results.

The formulation of resorcinol‐formaldehyde adhestves

AbstractAfter a brief review of previous work experiments are described showing the effect of formulation and conditions of production on the stability or shelf life of resortinol‐formaldehyde condensation products. Consideration is given at the same time to the best means of causing the condensation product to set to a strong cement. Examples are given, using an asbestos base laminated plastic, of the shear strength of lap joints from suitably formulated cements. The effect of immersion of these joints in boiling water, dilute acids and alkalis and the effect of exposing them to very dry and very humid atmospheres is described.