Joint Bondline Research Articles

Reinforced Solder Technology for Increased Reliability

Abstract The reliability of solder joints have been studied for many years. The selection of a solder for a particular application is often limited based on melting point requirements. This limits the number of options that are available for use. When alloy selection options are limited, people look to process changes to try and improve the reliability. Two such areas that have been identified that can impact reliability are bondline control and void reduction. This paper analyzes a new reinforced solder technology to maintain a consistent solder joint bondline. Experiments were also conducted to determine how best to design these preforms to minimize voiding.

Enhancement of static strength and long term durability of steel/epoxy joints through a fiber laser surface pre-treatment

The aim of this work is to investigate the effectiveness of laser irradiation on steel substrates for adhesive bonding. The evolution of surface topography and wettability for various pulse fluencies was investigated. The most suitable processing conditions were then selected and adhesive bonded steel/epoxy single-lap and T-peel joints were prepared for static testing. Moreover, in order to assess joint strength against environmental attack, an additional batch of samples was subjected to hydrothermal cycling before testing. The obtained results were compared with baseline samples fabricated using degreasing and sand blasting surface pre-treatments. Post-failure SEM analyses of fracture surfaces were undertaken to survey the locus of failure within the joint bond-line. Results indicated that laser irradiation effectively enhances the overall mechanical behavior of the joint under shear and peel loading. In addition, it allows to retain joint strength after exposure to aggressive environmental conditions.

Automotive Material Sustainability Through Reversible Adhesives

AbstractThis communication defines the key existing technologies for reversible adhesion and bonded joint disassembly, and introduces the reader to early experimental findings on the use of thermally labile functional additives in an adhesive matrix. These additives have been found to induce localized, out of plane stresses in a joint's bondline, allowing for an adhesive disbond. It has been found that the additive and adhesive matrix combination is key to the relationship between joint disassembly and joint strength.

Three-Dimensional Finite Element Analysis of the Stress Distribution in Bi-Adhesive Bonded Joints

A 3-D elastic finite element model was developed to investigate the stresses distribution of bi-adhesive bonded joints (i.e., the bond line of joints filled with two adhesives of dissimilar toughness). The effects of the loading mode on the stress distribution of joints, including the single-lap joints under tensile loading (i.e., single-lap joints) and the butt joints under cleavage loading (i.e., cleavage joints), were also studied in detail. Results showed that higher stress, distributed at the contact position of the dissimilar adhesives placed along the bond line of bi-adhesive bonded joints. Also, the maximum stress of the adhesive layer decreased when the length ratios and bonding sequence along the bond line, filled with two dissimilar adhesives, was appropriately designed. At the same time, stress convergence in the adhesive layer of bi-adhesive joints was also obviously reduced in contrast to the mono-adhesive joints. The numerical investigation shows that it is necessary to take into account the change of loading modes when optimizing the bi-adhesive joint design, because of the uneven and complex loading modes of the adhesive bonding structure in the engineering applications.

Tensile and creep properties of diffusion bonded titanium alloy IMI 834 to gamma titanium aluminide IHI Alloy 01A

Diffusion bonding of the Ti-alloy Ti–5.8Al–4.0Sn–3.5Zr–0.7Nb–0.5Mo–0.35Si–0.06C (wt%) to the intermetallic γ-based alloy Ti–33Al–2Fe–1.8V–0.1B (wt%) using hot isostatic pressing at 900°C, 200 MPa held for 1 h was studied. Sound joints without any pores or cracks with a width of approximately 5–7 μm could be produced. Tensile testing showed that the strengths of the joints are similar to the strength of the γ-TiAl base material at temperatures between room temperature and 600°C. The fracture occurs either at the joint or in the γ-TiAl material. The fracture initiation process is a competition between initiation in the γ-TiAl base material and initiation at the γ-TiAl/diffusion bond interface. Creep testing showed that most of the creep elongation occurs in the Ti-alloy, but failure is initiated in the joint bond line. Creep causes degradation and pore formation in this line. Interlinkage of these pores creates a crack which grows slowly until the fracture toughness of the γ-TiAl is exceeded and the crack starts to propagate in the γ-TiAl material and terminates creep life.

Ultrasonic Study of Environmental Damage Initiation and Evolution in Adhesive Joints

Abstract This article reports on an experimental study of environmental degradation of adhesive joints by an ultrasonic angle-beam technique. The technique is based on measurements of the frequency response of the reflection of obliquely incident ultrasonic signals from a joint bondline. Ultrasonic measurements were performed using a special ultrasonic goniometer with only one ultrasonic transducer. By this method, the degradation of single lap adhesive joints was studied as a function of exposure in NaCl solutions at 68°C under static tensile load. It was found that joint degradation is accompanied by a shift of the ultrasonic reflection spectrum minimum to a lower frequency. Two stages of adhesive joint environmental degradation can be distinguished: a) a relatively slow adhesive joint degradation dominated by adhesive creep, and b) delamination along the adhesive/adherend interface, leading to failure. Several degradation mechanisms are found in the first stage to affect the position of the spectral minimum. The first is adhesive creep caused by normal-to-bond-plane stress concentration at the joint overlap edges. This mechanism is found to have the dominant effect on the ultrasonic signature. Second, changes of the effective density and elastic moduli of the adhesive layer also affect the spectrum of the reflected signal. The third mechanism is the degradation of the adhesive-adherend interface. In the second stage of the joint degradation process, delamination along the adhesive/adherend interface occurs and is followed by joint failure. While the time span of the first stage changes significantly from joint to joint, the time span of the second stage (failure by delamination) in our conditions is about 30–40 h. The delamination results in a significant additional spectral minimum shift to a lower frequency that can be used as an indicator of failure initiation.

Ultrasonic Study of Environmental Damage Initiation and Evolution in Adhesive Joints

This article reports on an experimental study of environmental degradation of adhesive joints by an ultrasonic angle-beam technique. The technique is based on measurements of the frequency response of the reflection of obliquely incident ultrasonic signals from a joint bondline. Ultrasonic measurements were performed using a special ultrasonic goniometer with only one ultrasonic transducer. By this method, the degradation of single lap adhesive joints was studied as a function of exposure in NaCl solutions at 68°C under static tensile load. It was found that joint degradation is accompanied by a shift of the ultrasonic reflection spectrum minimum to a lower frequency. Two stages of adhesive joint environmental degradation can be distinguished: a) a relatively slow adhesive joint degradation dominated by adhesive creep, and b) delamination along the adhesive/adherend interface, leading to failure. Several degradation mechanisms are found in the first stage to affect the position of the spectral minimum. The first is adhesive creep caused by normal-to-bond-plane stress concentration at the joint overlap edges. This mechanism is found to have the dominant effect on the ultrasonic signature. Second, changes of the effective density and elastic moduli of the adhesive layer also affect the spectrum of the reflected signal. The third mechanism is the degradation of the adhesive-adherend interface. In the second stage of the joint degradation process, delamination along the adhesive/adherend interface occurs and is followed by joint failure. While the time span of the first stage changes significantly from joint to joint, the time span of the second stage (failure by delamination) in our conditions is about 30–40 h. The delamination results in a significant additional spectral minimum shift to a lower frequency that can be used as an indicator of failure initiation.

Ultrasonic Study of Environmental Damage Initiation and Evolution in Adhesive Joints

This article reports on an experimental study of environmental degradation of adhesive joints by an ultrasonic angle—beam technique. The technique is based on measurements of the frequency response of the reflection of obliquely incident ultrasonic signals from a joint bondline. Ultrasonic measurements were performed using a special ultrasonic goniometer with only one ultrasonic transducer. By this method, the degradation of single lap adhesive joints was studied as a function of exposure in NaCl solutions at 68°C under static tensile load. It was found that joint degradation is accompanied by a shift of the ultrasonic reflection spectrum minimum to a lower frequency. Two stages of adhesive joint environmental degradation can be distinguished: a) a relatively slow adhesive joint degradation dominated by adhesive creep, and b) delamination along the adhesive/adherend interface, leading to failure. Several degradation mechanisms are found in the first stage to affect the position of the spectral minimum. The first is adhesive creep caused by normal-to-bond-plane stress concentration at the joint overlap edges. This mechanism is found to have the dominant effect on the ultrasonic signature. Second, changes of the effective density and elastic moduli of the adhesive layer also affect the spectrum of the reflected signal. The third mechanism is the degradation of the adhesive—adherend interface. In the second stage of the joint degradation process, delamination along the adhesive/adherend interface occurs and is followed by joint failure. While the time span of the first stage changes significantly from joint to joint, the time span of the second stage (failure by delamination) in our conditions is about 30—40 h. The delamination results in a significant additional spectral minimum shift to a lower frequency that can be used as an indicator of failure initiation.

Behaviour of Bombarded Ar at Surface and Bonded Interface of Copper

Argon ion bombardment is known to be effective in removing all surface contaminations and oxides and improving the quality of diffusion bonds. However, recent work has shown that the accelerating voltage used during the ion bombardment significantly affected the bond strength. This work has been carried out to investigate the behaviour of argon at the surface and bonded copper interface after argon ion bombardment. To investigate changes at the surface and the bonded interface, surface composition, surface morphology, gas in voids at the interface were monitored using Auger spectroscopy, reflection high energy electron diffraction (RHEED), and mass spectroscopy. This study shows that an increase in time or accelerating voltage of ion bombardment results in much surface damage by the increase in surface roughness and crystal disorder due to the ions the penetrating the surface and displacing atoms. Argon entrapped at the surface layer diffuses into the voids at bond-line of joints which are made using specimens treated by the argon ion bombardment. The presence of argon in the voids is one reason for the deterioration of the joints, in the specimens bombarded at a high accelerating voltage. When the specimens treated by ion bombardment are heated, argon gas is released from the surface. Heat treatment of specimens treated by ion bombardment is effective in restoring the surface to its original order and producing joints free from voids at the bond-line.

Space Shuttle redesigned solid rocket motor field joint verification

The internal insulation in the Space Shuttle redesigned solid rocket motor field joint was designed to provide thermal protection to the steel case and O-ring seals. An unvented design concept was chosen to prevent hot chamber gases from reaching the inner joint. The joint design was verified through flow/thermal analyses and tests. Postulated flaws and subsequent leak paths through the joint bondline and O-ring seals were analyzed to verify that the joint would perform adequately under these undesired conditions. Tests of static motors with flawed joints paralleled the analysis effort, verifying design insensitivity to manufacturing flaws and subsequent leak paths. Results of tests and analyses showed that the design met all performance and safety requirements.