Adhesive joints analysis

Sheppard, A., Kelly, D., Tong, L., (1998), Int. J. of Adhesion and Adhesives 18, 385. Wemersson, H., (1994), Fracture characterization of wood adhesive joints. Report TVSM-1006, Lund University, Division of Structural Mechanics, Lund, Sweden, Simon, F., Morel, S., Valentin, G. (1997). In Proceedings of the Euromech Colloquium 358, Mechanical behaviour of adhesive joints, analysis, testing and design, Pluralis, Paris, pp. 341-351. 

Crocombe, A.D. and Tatarek, A., A unified approach to adhesive joint analysis. In Proceedings of Adhesives, Sealants and Encapsulants 85. Plastics and Rubber Institute, London, 1985. 

The analysis of the test results shows that non-defect adhesive joints of the carbon plastic are acoustically less active than the glued main material. This can be explained by absence of plasticization effect of the die (adhesive layer). The value of the breaking point ("C ) at the adhesive joints shift is 9,6 M Pa. 

The path of failure of an adhesive joint can give information about the mechanism of failure if analysis of the elemental and chemical composition can be conducted along the path. Several authors have performed such analyses by loading the adhesive joint until it fractures and then using XPS to analyze each side of the fracture. 

Table 1 contains the metal-to-metal engineering property requirements for Boeing Material Specification (BMS) 5-101, a structural film adhesive for metal to metal and honeycomb sandwich use in areas with normal temperature exposure. The requirements are dominated by shear strength tests. Shear strength is the most critical engineering property for structural adhesives, at least for the simplistic joint analysis that is commonly used for metal-to-metal secondary structure on commercial aircraft. Adhesive Joints are purposefully loaded primarily in shear as opposed to tension or peel modes as adhesives are typically stronger in shear than in Mode I (load normal to the plane of the bond) loading. 

Daghyani. H.R.. Ye. L. and Mai. Y.W. (1995b). Mode I fracture behaviour of adhesive joints, 2, Stress analysis of constraint parameters. J. Adhesion 53, 163-172. 

Ion beams provide useful information either as a diagnostic tool or as a precision etching method in adhesion research. The combination ISS/SIMS method used along with other techniques such as SEM provides a powerful tool for elemental analysis of surface composition. These results, as well as earlier work in this laboratory, indicate that the surface composition can be significantly different from the bulk due to contamination, selective chemical etching and segregation. These same techniques also provide an analysis of the mode of failure in adhesive joints. Many failures classified as "adhesive" on the basis of visual inspection are frequently mixed mode failures or failures at a new interface containing elements of both adhesives and adherend. 

Life prediction methodology embraces all aspects of the numerous processes that could affect the function of the element—in this case the bulk adhesive. The first step is to define the function of the adhesive clearly enough for a failure criterion to be derived. This failure criterion may be an unacceptable reduction in tensile strength, time to creep failure under a given stress, reduction in modulus due to moisture ingression, increase in modulus due to oxidation, unacceptable crack depth, or a variety of other possible criteria. It is also important that the criteria be related to practical adhesive joint performance. This is where it is difficult, and one must presume, at least for this limited analysis, that the adhesive will fail via a bulk (cohesive) property. 

Because of the high scattering of experimental results and the great difficulty in reaching the fully cohesive failure of wooden adhesive Joints, a numerical analysis has been made to give a better knowledge of their mechanical behaviour for various parameters (adhesive used. Joint thickness, loading mode, etc...). For the PU resin tested previously in shear, such an analysis has been made on two steps first simulations have been made on bulk adhesive specimen to determine the mechanical behaviour of the resin and the numerical results obtained have been implanted in the FE code CASTEM 2000 [21] for the mTENF bonded specimen loaded by shear. 

X-ray radiography of nickel-coated fibers, surface atoms of hydroxyapatite, coating analysis of silane treated hydroxyapatite, and composition of the failure area of an adhesive joint between rubber and metal. This review of applications shows that carbon fibers are the most frequently tested material by XPS. 

In selecting an adhesive system, one must calculate the strength required. If, for example, you wish to design an adhesive-bonded lifting device for a 50 lb (23 kg) machine component, you can use an adhesive with a 100 psi (0.689 MPa) shear strength and make the bond area 0.5 in (3.2 cm ). You must use this type of joint-strength analysis in all adhesive-joint designs [Ref. 4, pp. 171-172]. 

In any case, both the FEA/ERR analysis from this study and the experimental results cited from the literature clearly demonstrate the importance of considering adherend thickness in the design of Joints. Test results and commonly used design rules that ignore this aspect of adhesive joints should be used with great caution. 

This paper wiU build on previous reviews which have sought to explore the marmer in which surface analysis methods can be purposefully employed to understand adhesion phenomena [4—6], with an emphasis on the elucidation of interphase chemistry. The rationale behind such an approach is that it is this critical region of a polymer/metal or polymer/polymer couple that will influence the performance of the overall system, be it the durability of an adhesive joint or the corrosion protection performance of an organic coating. 

Sound knowledge of the joint behavior is required for a successful design of bonded joints. To characterize the bonded joint, the loading in the joint and the mechanical properties of the substrates and of the adhesives must be properly defined. The behavior of the bonded joint is investigated by finite element (FE) analysis methods. While for the design of large structures a cost-efficient modeling method is necessary, the nonlinear finite element methods with a hyperelastic material model are required for the detailed joint analysis. Our experience of joint analysis is presented below, and compared with test results for mass transportation applications. 

A. Surface Free Energies. Surface free energies must dominate any explanation of the adhesion between different phases which are not mechanically linked. Current levels of understanding of adhesiveness are such that actual adhesive strengths are always much less (1-0.1%) than those predicted by thermodynamic analysis, and often there is apparently little correlation between the two. Further refinement of the theory of adhesiveness will require understanding of the importance of flaws in an adhesive joint and of the relative contributions of polar and dispersive Van der Waal s interactions. The following is an analysis of adhesion in terms of surface free energies. 

It is worth noting that at the minimum value of d = 2, value A becomes negative. That means, in accordance with Equation (12.1), that tan < tan 8m- In other words, at small d (smooth surfaces of the filler particles) the packing of the polymer molecules at the interface may be more dense compared with the bulk. This fact leads to the diminishing molecular mobility in the interfacial layer [1, 37, 38] Extrapolation of the dependence of A on d to maximum value of d = 3 gives the limiting value of A 4.5. This value meets the value A = 4.2, that was derived from the extrapolation of the volume of the interfacial layer on d to d = 3 [39]. Thus, this analysis allows an estimation of the structural factors influencing formation of the adhesion joints. The main factors are fractal dimensions of the particle surface, d and of the polymer df, which determine adhesion at the polymer-filler particle interface. 

D. E. Packham, Topography on the Adhesive Joint Proc. 6th Int. Conf. on Adhesion and Surface Analysis, Loughborough, April 2000, p. 41. 

The analysis of these resins is diflScult when unknown products, particularly fully cured have to be tested for UF and MF resins. Widmer [50] offers a method for the identifieation of UF and MF resins in technical products. This involves preparing erystalline produets of urea and melamine and identifying them under the microseope. Melamine (in the form of melamine crystals) and urea (in the form of long, crystalline needles of urea dixanthate) can be seen. This method allows one to distinguish between urea and melamine even in a cured adhesive joint. 

Analysis of Strength Criteria as Applied to Adhesive Joints... 

As shown earlier, adhesive joints are considered to be systems unequally resistant to the stresses of normal fracture and compression. Thus, it is expedient to limit our analysis to strength theories and the Mohr theory as the pure experimental one. 

This brief analysis of the latest energetic strength theories suggests the possibility of investigating their applicability to adhesive joints from the following considerations ... 

---