Adherend Materials Research Articles

Experimental determination of impact tensile properties of adhesive butt joints with the split Hopkinson bar

The tensile strength and energy absorption of adhesive butt joints at high rates of loading are determined with a tensile split Hopkinson bar using a cylindrical specimen. A commercially available single-component cyanoacrylate adhesive (instantaneous adhesive) and two different adherend materials are used in the adhesion tests. The impact tensile strength of the cyanoacrylate adhesive butt joints is determined from the applied tensile stress history at failure initiation. The impact absorbed energy is obtained by numerical integration of dynamic tensile load-adhesive deformation data. Comparative tension tests at low and intermediate rates of loading are performed on an Instron testing machine. An axisymmetric finite element analysis is carried out to investigate the stress distributions in the adhesive layer of the cyanoacrylate adhesive butt joints. The effects of loading rate, adherend material and adhesive layer thickness on the tensile strength and energy absorption of the cyanoacrylate adhesive butt joints are examined in detail. It is shown that the joint tensile strength increases significantly with increasing loading rate and is greatly affected by both the adhesive layer thickness and the adherend materials. The limitations of the technique are discussed.

620 アクリル系接着剤の繰り返し衝撃負荷に対する引張強度

The impact fatigue strength of the acrylic adhesive under impact tensile loading was evaluated by adding impact cyclic loads to a tubular butt joint. The material of adherends was aluminium alloy A5052-H34,and the acrylic adhesive Hardloc M-372-20 was used. First, the combined loading test was performed in order to evaluate the static strength of the adhesive. As a result, the value of fracture stress under shear load is stronger than the value of fracture stress under tensile load. As the adhesive layer thickness become thick, the value of fracture stress become low. In the impact fatigue test, the thickness of the adhesive layer was 0.1mm. As a result, the maximum incidence stress becomes low, the number of impact loads to a fracture will increase. In cace the insident stress is 9MPa, the specimen did't fracture even if it was subjected to the impact loads 1 million times. It was considered that the fatigue limit is 9MPa.

Effect of Environment on Fracture Toughness and Debond Growth of Aluminum/FM®73/Boron-Epoxy Adhesively Bonded Joints

Tests were conducted to determine the fracture toughness of aluminum/FM®73/boron-epoxy adhesively bonded joints. Double cantilever beam (DCB) specimens and end-notched flexure (ENF) specimens were exposed to one of the following environments: hot/wet (71° C(160° F) and >90% RH) conditions for 5000 h, thermal cycles between 71° C (160° F) and −54° C (−65° F), or an outdoor “rooftop” environment for 10 000 h. The environmentally exposed specimens were tested along with as-received (or unexposed specimens). The different adherend materials had different coefficients of thermal expansion (CTE). The mismatch of CTE between adherends caused residual thermal stresses in the adhesive joints at every temperature other than the elevated cure temperature. The residual stresses could not be accounted for with closed form solutions. Finite element analysis (FEA) of the specimens was required. Using FEA solutions, it was determined that the fracture toughness of the environmentally exposed specimens was lower than the as-received specimens for every environment tested for both DCB and ENF specimens.

衝撃曲げモーメントを受ける異種材料スカーフ接着継手の有限要素応力応答解析

The stress wave propagation and the stress distribution in adhesive scarf joints with dissimilar adherends subjected to impact bending moments are analyzed in an elastic deformation using three-dimensional finite-element method (FEM). An impact load is applied to the joint by dropping weight. The one side of the adherend is fixed and the other side of the adherend is subjected to an impact load. FEM code employed is DYNA3D. The effects of scarf angles of the adherends, the adhesive thickness and Young's modulus of the adhesive, the combinations of materials of the adherends on the stress propagation and distributions at the interfaces are examined. The scarf angles are changed from 15 to 90 degrees. It is found that the maximum value of the Mises' equivalent stress σM appears at the interface between the adhesive layer and the adherend made of mild steel, and it is independent of the combinations of the adherend materials. In the case where the scarf angle is 45 degree, the maximum value of the Mises' equivalent stress σM is minimal. The stress σX is the greatest in all of stress components. The maximum value of the Mises' equivalent stress σM increases as the adhesive layer thickness and Young's modulus of the adhesive increase. It is seen that the position where the maximum value of the Mises' equivalent stress σM occurs moves toward edge of the adhesive interface as the thickness and Young's modulus of the adhesive increase. In addition, experiments were carried out to measure the strain response of the adhesive scarf joints subjected to impact bending moments using strain gauges. A fairly good agreement is seen between the analytical and the experimental results.

Predicted thermal stresses in a bimaterial assembly adhesively bonded at the ends

The interfacial shearing and “peeling” stresses in an elongated bimaterial assembly, adhesively bonded at the ends and subjected to the change in temperature, are predicted, based on an approximate structural analysis (strength-of-materials) model. The stresses in the bonded joints due to the thermal expansion (contraction) mismatch of the adherend materials within the bonded areas (“local” mismatch), as well as the stresses, caused by the thermal mismatch of the adherend materials within the unbonded midportion of the assembly (“global” mismatch), are considered. The interaction of the “local” and the “global” stresses is evaluated and analyzed. It is shown that if the bonded joints are made long enough, the maximum stresses in the assembly will not be different from the stresses in an assembly with a continuous adhesive layer, no matter how long the unbonded midportion of the assembly might be. The obtained results can be helpful in the stress–strain evaluations and physical (mechanical) design of bimaterial assemblies in electronic and photonic packaging.

Evaluation of impact tensile properties of adhesive butt joints

The tensile properties of adhesive butt joints under impact loading are measured with a modified split Hopkinson bar using a solid butt joint specimen. A commercially available cyanoacrylate adhesive (commonly termed an instantaneous adhesive) and two different adherend materials (or substrates) are used in the adhesion tests. The impact tensile strength of the cyanoacrylate adhesive butt joints is determined from the applied tensile stress at failure initiation. The impact energy absorbed is obtained by numerical integration of dynamic load-displacement data. Comparative tension tests at low rates of loading are performed on an Instron testing machine. The effects of loading rate, adherend material and thickness of the adhesive layer on the tensile strength and energy absorption of the cyanoacrylate adhesive butt joints are examined in detail.

Environmental durability of moisture-cured urethane adhesive joints

Hot-dipped galvanized steel was bonded to fiber-reinforced unsaturated polyester (FRP) with a moisture cure urethane. Single lap shear joints were made with bondline thicknesses of 0.76 mm and bond areas of 25.4 mm×25.4 mm. Single lap shear joints were aged by cataplasma, cyclic moisture, QUV ®, Weather-Ometer ® and an oven at 60°C. Cataplasma aging and cyclic moisture aging resulted in a 23 and a 28% drop, respectively, in lap shear strength of joints made with acetone-wiped surfaces. QUV ® and oven aged joints resulted in increased lap shear strength, and oven aged joints changed in failure mode from adhesive at the galvanized steel interface to cohesive failure. Weather-Ometer aged joints failed adhesively at the FRP interface, but after closer inspection by environmental scanning electron microscope (ESEM) adhesive could be seen on the surface of the FRP. QUV ® light may not always penetrate the adherend materials even though natural sunlight penetrates the same materials. When conducting accelerated aging of adhesive joints made with FRP adherends that allow light to penetrate to the joint, workers must carefully consider the light source and adherend material used in the design of accelerated aging experiments.

Theoretical and experimental studies for the failure criterion of adhesively bonded joints

The objective of this work was to develop a criterion for predicting the failure strength of joints bonded by ductile adhesives. To obtain the criterion, first, fracture tests were carried out on T-peel joints and single-lap joints with various joint geometries, adhesives, and adherend materials. Then using the fracture loads obtained in the tests, a finite element analysis was performed by which the stresses in the adhesive joints were calculated. It is concluded that the failure of an adhesively bonded joint occurs when the maximum of the ratio of the mean to effective stresses exceeds a certain value, which can be considered a new material constant of a ductile adhesive.

Details of the integral equation method applied to the analysis of an adhesive layer crack

The mathematical model for a crack in an elastic adhesive layer sandwiched between two adherends proposed by Fleck, Hutchinson and Suo ((1991) Crack path selection in a brittle adhesive layer. International Journal of Solids and Structures27(13), 1683–1703) was considered. The elastic mismatch between the adhesive and adherend materials modifies the far-field values of the stress intensity factors and of the T-stress in a manner that depends on the position of the crack inside the layer and on the Dundurs parameters. A complex-potential stress-function formulation, using dislocation distributions represented by truncated Chebyshev series, yielded an integral equation that was solved numerically by the method of collocations. The symbolic derivation of the integral equations was checked, and a few differences from Fleck, Hutchinson and Suo's expressions were identified and reconciled. The computational aspects of the solution were studied in detail using two programming languages, MATHCAD and C++, run on standard PC hardware. A palette of numerical techniques were utilized to study and control the consistency and accuracy of the solution. Symmetry and anti-symmetry arguments were used to identify numerically sensitive regions. Fast Fourier Transform calculation of sine and cosine Fourier integrals was used to increase speed. Convergence of intermediate and final results was examined. It was found that the method is very sensitive to the details of numerical computation, especially for combinations of parameters that lead to nearly singular matrices.

Evaluation of Impact Shear Strength of Adhesive Joints with the Split Hopkinson Bar.

The shear strength of adhesive joints at high loading rates is evaluated with the split Hopkinson bar technique using a pin-and-collar specimen. A commercially available cyanoacrylate adhesive(commonly termed an instantaneous adhesive)and two different adherend materials are used in the tests. The impact shear strength of the cyanoacrylate adhesive joints is determined from the applied shear stress history at failure initiation. Comparative shear tests at low loading rates are carried out on an Instron testing machine. The influences of loading rate, thickness of adhesive layer, and adherend materials on the shear strength of the cyanoacrylate adhesive joints are examined. The test results indicate that the shear strength increases significantly with increasing loading rate, and is greatly affected by both the adhesive layer thickness and adherend materials. It is shown that the shear strength increases to a maximum at an adhesive layer thickness of about 25 μm and subsequently decreases. The advantages and limitations of the technique are also discussed.

Adhesion Energy Measurements of Multilayer Low-K Dielectric Materials for ULSI Applications

ABSTRACTCurrently, the IC industry is researching the integration of a variety of materials to meet the low dielectric constant requirement for improved back-end of line (BEOL) interconnect performance. One critical dimension for successful ntegration of these new materials is maintaining mechanical integrity through multilayer processes. This includes both cohesive and adhesive fracture resistance. The latter adds additional complexity in that adhesive toughness is a function of the adherend materials and the processes used to join them. Hence, many good dielectric materials may be rematurely eliminated from further research not because of inherently poor adhesion but because of the necessity to optimize processing strategies.In this paper, we use the modified Edge Liftoff Test (m-ELT) to quantify the mechanical adhesion of multilayer blanket coatings. A specific example is used to demonstrate the utility of combining the m-ELT with surface analysis to optimize the reliability of low-K dielectric resins for use in ULSI applications. The system studied consists of a Cyclotene™5021(BCB) low-K material integrated with CVD aluminum for single level, damascene structures. The effects of liner layer metallurgy and surface plasma treatments are measured. Surface analysis is done on the failed parts to understand the location of the failure. In this way recommendations for process optimization can be made.

Determination of Impact Shear Strength of Adhesive Bonds with the Split Hopkinson Bar.

The impact shear tests on a cyanoacrylate based adhesive (hereafter referred to as the CA adhesive) are conducted by means of a modified split Hopkinson bar using a pin-and-collar specimen. Two adherend materials (or bearing steel and 7075-T 6 Al alloy) are used in the tests. The impact shear strength of the CA adhesive bonds at loading rates of the order of 106 MPa/s is determined from the peak value of the applied shear stress history in the bond-line. Comparative shear tests at low loading rates are carried out on the same design of specimen in an Instron testing machine. The effects of loading rate, thickness of adhesive layer and adherend materials on the shear strength of the CA adhesive bonds are examined. The test results indicate that the shear strength of the CA adhesive bonds increases significantly with increasing loading rate, and is much affected by both the thickness of adhesive layer and the adherend materials.

Process‐induced effects in thin‐film bonding of PEKEKK in metal‐polymer joints

AbstractIn this work, poly ether ketone ether ketone ketone (PEKEKK) was used as a thermoplastic adhesive for joining metals. Titanium and cobalt chromium alloys were joined to form tensile butt joints. These tensile specimens were used to evaluate bond performance. A controlled thermal processing cycle was used to modify and enhance the polymer crystallinity during bonding. The resulting effects on bond performance were examined. The process window for a thermal bonding process was identified. Factorial experiments were conducted to determine the effects of modifications to adhesive and adherend material, and bonding pressure on bond performance. A titanium alloy and a cobalt chromium alloy were used as the adherends. Understanding changes in the thermoplastic adhesive joint with the variation of process parameters will allow for proper application and processing of thermoplastic structural adhesives.

Fracture Behavior and Strength of Stepped-Lap Bonded Joint with Adhesive Resin under Tensile Loading

Nonlinear fracture behavior of stepped-lap bonded joints is studied. The joints used have adherends of eight kinds of metals: three of carbon steel, four of aluminum alloy and one of brass. The joints also have various thicknesses, lap lengths and step numbers. The effect of Young's modulus and yield strength of adherend material on the joint strength is calculated by means of elastoplastic finite-element analysis. It is found that the strength of the joint which yields at an adherend corner is nearly equal to the yield strength of the adherend material, because the displacement of the adhesive layer increases abruptly after the adherend yield and exceeds the layer's deformation capacity. The joint strength diagrams obtained by the strength prediction method applying our adhesion criteria show good agreement with the experimental results for all currently available joints having various dimensions and materials.

Brazing residual stresses in Glidcop-Al12SiBe

Brazing of Glidcop to beryllium by using Al12Si has been considered. Brazinng residual stresses have been determined by a finite element method. Temperature-dependent elastic properties and coefficients of thermal expansion have been used. Plastic deformation of the brazing alloy, based on experimental stress-strain curves for Al12Si at different temperatures, has been included in the FEM analysis. It has been shown that the plastic deformation of the brazing layer, even if only 50 μm thick, affects the residual stresses considerably. In general, a decrease of the residual stresses with increased Al12Si layer thickness has been observed. Successful brazing may require a thickness of 500 μm or larger. The calculated residual stresses are produced as a result of the brazing operation because of the thermal expansion mismatch of the adherend materials. The effects of the subsequent service conditions such as mechanical loading, thermal gradients, and neutron irradiation on the material properties and the residual brazing stresses have not been considered in this paper.

Effect of thermal residual stress on the crack path in adhesively bonded joints

Mode I fracture behaviour of adhesively bonded double and cantilever beam (DCB) compact tension (CT) joints was studied using a rubber-modified epoxy (Araldite® GY260) as the adhesive. Adherends were prepared from a carbon fibre (CF)/epoxy composite or aluminium alloys. The crack path in the joints was studied based on the sign of the non-singularT-stress ahead of the crack tip by calculating the thermal residual stress in the joints using finite element analysis. The results indicate that the type of adherend materials influence the level of the thermal residual stress in the adhesive layer, which consequently causes different crack paths in the joints, i.e. a uniformly smooth fracture surface in both CT and DCB aluminium joints and a wavy crack growth in the DCB CF/epoxy composite joints. However, the fracture energies of different types of adhesive joints were almost identical to each other for bond thicknesst<0.2 mm, and a somewhat higher fracture resistance was obtained for the CF/epoxy DCB joints with large bond thickness.

Hydrothermal stability of joints, using a silicone rubber adhesive, for a range of adherends of interest to makers of surgically-implanted microelectronic devices

Most designs for a microelectronic implant require an encapsulant of some kind. The working life of a device, when implanted, depends upon sustained adhesion, in the presence of body fluid, between the encapsulant and the underlying structure encapsulated. This paper describes a series of accelerated life test on the adhesion between a convenient silicone rubber (Dow Corning 3140) and a range of adherend materials of which such structures might be made. It appears that bonding is by chemisorption and varies in resistance to degradation in water according to the density of negative charge on the adherend surface. The work is thought to provide the beginnings of a rational process for choosing adherend materials in implant design.

Measurement of IC Molding Compound Adhesion Strength and Prediction of Interface Delamination Within Package.

The adhesion strength evaluation of molding compounds is a critical issue in structural design and material selection of IC plastic packages, because interface delamination is a main cause of package failure. We previously proposed a method that measures true adhesion strength without the effect of residual stress. This paper describes the dependence of true adhesion strength on adherend materials, temperature and molding compound moisture content as determined by this method. We have also tried to predict interface delamination within a package by comparing the measured strengths with thermal stress analysis results. The results suggest that interface delamination during soldering is caused by thermal stress and decrease in true adhesion strength caused by absorbed moisture rather than vapor pressure.

Fracture Behavior and Strength of Stepped-Lap Bonded Joint with Adhesive Resin Under Tensile Loading.

Nonlinear fracture behavior of stepped-lap bonded joints is studied. The joints used have adherends of eight kinds of metals : three types of carbon steel, and four types of aluminum alloy and brass. The joints also have various thicknesses, lap lengths and step numbers. The effect of Young's modulus and yield strength of adherend material on the joint strength is calculated by means of elasto-plastic finite element method analysis. It is found that the strength of the joint which yields at an adherend corner is nearly equal to the yield strength of the adherend material, because the displacement of the adhesive layer increases abruptly after the adherend yield, and exceeds the layer's deformation capacity. The joint strength diagrams obtained by the strength prediction method applying our adhesion criteria show good agreement with the experimental results for all the present joins having various dimensions and materials.

Composite-to-metal tubular lap joints: strength and fatigue resistance

The axial strength and fatigue resistance of thick-walled, adhesively bonded E-glass composite-to-aluminum tubular lap joints have been measured for tensile and compressive loadings. The joint specimen bonds a 63 mm OD aluminium tube within each end of a 300 mm long, 6 mm thick E-glass/epoxy tube. Untapered, 12.5 mm thick aluminium adherends were used in all but four of the joint specimens. The aluminum adherends in the remaining four specimens were tapered to a thickness of 1 mm at the inner bond end (the bond end where the aluminum adherend terminates). For all loadings, joint failure initiates at the inner bond end as a crack grows in the adhesive adjacent to the interface. Test results for a tension-tension fatigue loading indicate that fatigue can severely degrade joint performance. Interestingly, measured tensile strength and fatigue resistance for joints with untapered adherends is substantially greater than compressive strength and fatigue resistance. The joint specimen has been analyzed in two different ways: one approach models the adhesive as an uncracked, elastic-perfectly plastic material, while the other approach uses a linear elastic fracture mechanics methodology. Results for the uncracked, elastic-plastic adhesive model indicate that observed bond failure occurs in the region of highest calculated stresses, extensive bond yielding occurs at load levels well below that required to fail the joint, and a tensile peel stress is generated by a compressive joint loading when the aluminum adherends are untapered. This latter result is consistent with the observed joint tensile-compressive strength differential. Results of the linear elastic fracture mechanics analysis of a joint with untapered aluminum adherends are also consistent with the observed differential strength effect since a mode I crack loading is predicted for a compressive joint loading. Calculations and a limited number of tests suggest that it may be possible to selectively control the differential strength effect by tapering the aluminum adherends. The effect of adherend material and thickness on fracture mechanics parameters is also investigated. The paper concludes by examining the applicability of linear elastic fracture mechanics to the joints tested.