Bondline Region Research Articles

Viscoelastic mapping of spruce-polyurethane bond line area using AM-FM atomic force microscopy

Amplitude modulation-frequency modulation atomic force microscopy (AM-FM AFM) with the capability of mapping simultaneously the topography and the nanomechanical properties of materials provides elastic information including Young's modulus, and loss tangent as viscoelastic information. The AM-FM mode operating principle involves the excitation and detection of two cantilever resonances simultaneously. Amplitude modulation (AM), the first resonance, is used for tapping mode imaging, while a higher resonance mode is operated in frequency modulation (FM). At resonance, the cantilever frequency and phase respond sensitively to changes in sample properties to provide a direct measurement of substrate mechanical properties and compositional information that only requires tuning of the cantilever resonance to provide quantitative information. In this study for the first time, by using an AM-FM AFM, the viscoelastic properties of the spruce wood and polyurethane adhesive (PUR) bond line area as a part of cross laminated timber (CLT) system were investigated. It was found that PUR adhesive rarely penetrates into the wood, and in contrast to viscous properties (tan δ), the elastic properties increase from the wood part towards the adhesive part in the bond line. AM-FM AFM technique proved to be able to effectively map viscoelastic properties of bond line region.

Probabilistic stress variation studies on composite single lap joint using Monte Carlo simulation

The work presented in this paper involves the stochastic finite element analysis of composite-epoxy adhesive lap joints using Monte Carlo simulation. A set of composite adhesive lap joints were prepared and loaded till failure to obtain their strength. The peel and shear strain in the bond line region at different levels of load were obtained using digital image correlation (DIC). The corresponding stresses were computed assuming a plane strain condition. The finite element model was verified by comparing the numerical and experimental stresses. The stresses exhibited a similar behavior and a good correlation was obtained. Further, the finite element model was used to perform the stochastic analysis using Monte Carlo simulation. The parameters influencing stress distribution were provided as a random input variable and the resulting probabilistic variation of maximum peel and shear stresses were studied. It was found that the adhesive modulus and bond line thickness had significant influence on the maximum stress variation. While the adherend thickness had a major influence, the effect of variation in longitudinal and shear modulus on the stresses was found to be little.

Mechanical Properties of Secondary Wall and Compound Corner Middle Lamella near the Phenol-Formaldehyde (PF) Adhesive Bond Line Measured by Nanoindentation

To find out the penetration of PF into the wood cell wall and its effects onthe mechanical properties in the cellular level, the elastic modulus and hardness of secondary wall (S2layer) and compound corner middle lamella (CCML) near PF bond line region were determined by nanoindentation. Compare to the reference cell walls (unaffected by PF), PF penetration into the wood tissues showed improved elastic modulus and hardness. And the mechanical properties decreased slowly with the increasing the distance from the bond line, which are attributed to the effects of PF penetration into S2layer and CCML. The reduced elastic modulus variations were from18.8 to 14.4 GPa for S2layer, and from10.1 to 7.65 GPa for CCML. The hardness was from 0.67 to 0.52 GPa for S2layer, and from 0.65 to 0.52 GPa for CCML. In each test viewpoint place, the average hardness of CCML was almost as high as that of S2layer, but the reduced elastic modulus was about 50% less than that of S2layer. But the increase ratio of mechanical properties was close. All the results showed PF penetrates into the CCML. The penetration behavior and penetration depth from bond line were similar in both S2layer and CCML.

Adhesive penetration of wood cell walls investigated by scanning thermal microscopy (SThM)

Abstract Cross sections of wood adhesive bonds were studied by scanning thermal microscopy (SThM) with the aim of scrutinizing the distribution of adhesive in the bond line region. The distribution of thermal conductivity, as well as temperature in the bond line area, was measured on the surface by means of a nanofabricated thermal probe offering high spatial and thermal resolution. Both the thermal conductivity and the surface temperature measurements were found suitable to differentiate between materials in the bond region, i.e., adhesive, cell walls and embedding epoxy. Of the two SThM modes available, the surface temperature mode provided images with superior optical contrast. The results clearly demonstrate that the polyurethane adhesive did not cause changes of thermal properties in wood cell walls with adhesive contact. By contrast, cell walls adjacent to a phenol-resorcinol-formaldehyde adhesive showed distinctly changed thermal properties, which is attributed to the presence of adhesive in the wood cell wall.

Improved mechanical properties in dissimilar Ti-AISI 304L joints

The effect of low temperature post weld heat treatment on the tensile strength and bend test properties of dissimilar friction welds between titanium and AISI 304L stainless steel joints is investigated. Post weld heat treatment at temperatures less than 873 K has no effect on joint tensile strength properties, but markedly improves bend test properties. The highest bend angle is produced using a post-weld heat treatment at 773 K for 1 h (the Larson-Miller parameter corresponding to this treatment is 15.5×103 K h−1). Low temperature heat treatment improves bend ductility, because stress relaxation occurs with minimal increase in the transition region width at the bondline region. Dissimilar joint bend testing properties decrease markedly when the width of the transition region exceeds 1–2 μm. An explanation for the detrimental effect of thick transition regions at the joint interface region on the mechanical properties of dissimilar joints is proposed. It is suggested that the development of significant triaxial stress due to the constraint imposed by large, needle-shaped intermetallic particles promotes premature joint failure in joints containing thick transition regions.

鉄基酸化物分散強化合金ＭＡ９５６の液相拡散接合現象と接合継手特性

In order to decrease the completion time during TLP-bonding, an iron-based filler metal, (IM-7) comprising MA956 base metal containing 7 mass%Si and 1 mass%B was developed to join MA956 base material. TLP-bonded joints free of microvoids and bondine intermetallic phases were obtained using a bonding temperature of 1563 K, a holding time of 2.16 ks and an applied pressure of 7.0 MPa. The bondline region in TLP-bonded MA956 base metal had a bamboo-like microstructure. In order to make clear the formation mechanism of this microstructure, the growth mechanism of solid phase during isothermal solidification was evaluated. During tensile testing at 923 K, the joints TLP-bonded at 1563 K-for 2.16 ks fractured in the base metal zone and consequently, the mechanical properties of the joint region and the base metal were similar. The creep rupture properties of the joint regions were close to the base metal properties in the transverse direction.

Influence of silicon in aluminium on the mechanical properties of titanium/aluminium friction joints

The influence of post-weld heat-treatment and of residual silicon in aluminium on the mechanical properties of dissimilar friction joints between titanium and aluminium was investigated. Although joint tensile strength and bend test properties were drastically reduced following post-weld heat treatment, the responses of Ti/h.p. Al and Ti/c.p. Al joints were quite different. The tensile strength and bend test properties of Ti/h.p. Al joints were markedly decreased by heat-treatments involving shorter holding times at lower temperatures. Joint failure in post-weld heat-treated joints was associated with Al3Ti formation at the bondline region. The growth rate of the Al3Ti intermetallic layer at the joint interface was much faster in post weld heat-treated Ti/h.p. joints. More than 20 at%Si segregated in the region between the titanium substrate and the Al3Ti intermetallic phase in heat-treated Ti/c.p. Al joints. It is suggested that silicon segregation retards Al3Ti formation by acting as a barrier to titanium and aluminium diffusion at the joint interface.

Particulate segregation and mechanical properties in transient liquid phase bonded metal matrix composite material

AbstractThefactors determining particulate segregation and joint shear strength in transient liquid phase (TLP) bonded aluminium based metal matrix composite (Mj1C) material are examined in the present paper. Three situations are evaluated during TLP bonding, namely, where the liquid width is unrestrained at the bonding temperature, where the liquid width is maintained constant, and where liquid is continuously expelled from the bondline region during the joining operation. Similar experimental and numerically calculated liquid width values are found during unrestrained liquid width TLP bonding (at the start of the isothermal solidification period). However, the calculated rate constant during isothermal solidification is smaller than in experimental testing. When liquid is expelled from the joint interface during TLP bonding at 853 K, the liquid width attains a constant value of ~55 μm. Although the completion time for isothermal solidification is substantially decreased when liquid is expelled from the ...

Particulate segregation and mechanical properties in transient liquid phase bonded metal matrix composite material

Thefactors determining particulate segregation and joint shear strength in transient liquid phase (TLP) bonded aluminium based metal matrix composite (Mj1C) material are examined in the present paper. Three situations are evaluated during TLP bonding, namely, where the liquid width is unrestrained at the bonding temperature, where the liquid width is maintained constant, and where liquid is continuously expelled from the bondline region during the joining operation. Similar experimental and numerically calculated liquid width values are found during unrestrained liquid width TLP bonding (at the start of the isothermal solidification period). However, the calculated rate constant during isothermal solidification is smaller than in experimental testing. When liquid is expelled from the joint interface during TLP bonding at 853 K, the liquid width attains a constant value of ~55 μm. Although the completion time for isothermal solidification is substantially decreased when liquid is expelled from the joint interface, particulate segregation is still observed in joints produced using 15 and 25 μm thick copper insert metals. Particulate segregation could only be prevented through the use of very thin (<15 μm) copper insert metals. Joint shear strength increases when the thickness of the copper insert metal is decreased and when the applied load increases during liquid expulsion bonding. Higher joint shear strength results from decreased particulate segregation in completed joints.MST/2037

Transient liquid phase diffusion bonding of iron base oxide dispersion strengthened alloy MA 956

To decrease the completion time during transient liquid phase (TLP) bonding, an Fe basedfiller metal (1M 7), comprising MA 956 base metal containing 7%Si and l%B (wt-%), was developed to join MA 956 base material. Transient liquid phase bonded joints free of microvoids and bondline intermetallic phases were obtained using a bonding temperature of 1563 K, a holding time of 2·16 ks, and an applied pressure of 7·0 MN m−2. The bondline region in the TLP bonded MA 956 base metal had a bamboolike microstructure which was considered to be peculiar to bonded oxide dispersion strengthened alloys. For this reason, the growth mechanism of the solid phase during isothermal solidification was evaluated. During tensile testing at 923 K, the joints TLP bonded at 1563 K for 2·16 ks fractured in the base metal zone and consequently the mechanical properties of the joint region and the base metal were similar. The creep rupture properties of the joint regions were close to the base metal properties in the transverse direction.MST/2042

Molecular-dynamics simulation of avalanche in adhesion in a two-dimensional solid.

Molecular-dynamics simulations of the approach of two-dimensional solid surfaces are presented. At very low temperatures the surfaces avalanche or collapse to form a strained solid with no defects. Such behavior is qualitatively similar to that predicted recently by energy-minimization approaches. We observe that as the temperature is increased, individual atoms on the surface become increasingly unstable and there is a tendency to form bridges and discrete voids in the bond-line region. This phenomenon gives rise to a glasslike state in the interfacial region and provides a driving force for the production of dislocations and other defects that are far removed from the interface.

Ultrasonic welding using tie‐layer materials. part II: Factors affecting the lap‐shear strength of ultrasonic welds

AbstractThe influence of tie‐layer Melt Flow Index on the lap‐shear strength of ultrasonic welds in oriented polypropylene (OPP) has been evaluated. The tie‐layer Melt Flow Index was varied from 0.03 dg/min to 2600 dg/min; the highest lap‐shear strength properties were obtained using tie‐layers that had melt flow index values between 30 and 100 dg/min. When using low Melt Flow Index tie‐layers, hot spot formation and concomitant changes in fusion zone and heat‐affected‐zone dimensions produced stress concentrations that promoted failure in oriented polypropylene material away from the bondline region. When very high Melt Flow Index (2600 dg/min) tie‐layers were used, the mode of failure during lap‐shear testing was a mix of cohesive, in oriented polypropylene, and adhesive failure. The molecular weight of material at the bondline was not markedly affected by the thermal cycle produced during ultrasonic welding. Only the flash ejected when using low Melt Flow Index tie‐layers exhibited any evidence of degradation; it is suggested that the ejected flash may have been degraded because of a combination of thermal, cavitation, and thermo‐oxidative processes.

The Stress Corrosion Performance of Diffusion-Bonded Nickel-Base Alloys

Abstract Excellent mechanical strength can be achieved in diffusion-bonded nickel-base alloys when approximately 0.01 mm of nickel is plated on the surfaces before bonding. However, rapid stress corrosion cracking (SCC) takes place in the bond line region when such materials are tested in high-purity water at 360°C. The failures are caused by the low concentration of chromium in the nickel-rich bond line region. Long-time high-temperature anneals to diffuse chromium into the bond line dramatically improve the stress corrosion resistance. Measurements of the local chromium in the bond line and separate tests of Ni-Cr binary alloys show that chromium contents approaching that of the bulk alloy are necessary to eliminate the cracking susceptibility.

Experimental Determination of the Variation in Shear Modulus Through the Interfacial Zone of an Adhesive

Abstract A gradient in shear modulus occurs in the interfacial accommodation zone (IAZ) of FM 73, a commercial film adhesive, bonded to aluminum. Such determination has been made by means of ultrasonic Rayleigh waves (surface waves) generated on successively exposed layers of the adhesive throughout the bondline region. Experimental Rayleigh wave apparatus is described which has been used to obtain the shear-modulus gradient in FM 73. Various substrate surface treatments and adhesive cure times were considered, demonstrating that the variation of shear modulus in the IAZ of FM 73 is independent of substrate treatment or cure time. Preparing the aluminum substrate with BAC results in an IAZ of greater extent than occurs with the other two treatments. Cure time does not affect the range of the IAZ, but does influence somewhat the shear modulus of the adhesive beyond the IAZ.

Shear modulus gradients in adhesive interfaces as determined by means of ultrasonic Rayleigh waves (II)

Ultrasonic Rayleigh wave measurements made earlier on several different types of adhesives have led to the finding of a distinct gradient in shear modulus through the interfacial accommodation zone. As reported here, different preparations of substrate appear to have little effect on the nature and extent of the modulus gradient. However, cure time is found to play a significant role concerning the very existence of a gradient in shear modulus through the bondline region of an adhesive. The stated gradient may be attributable to residual stress in the interfacial zone.