Joints - Stress Distribution

The most common assembly when bonding two surfaces together is to overlap them and most adhesive companies supply data in the form of lap shear strength. This format can teach us a great deal about bonding design (Fig. 7). 

Take a very rigid material, like glass, and bond two pieces together using a very low modulus adhesive. The low modulus will encourage any stress to be distributed uniformly over the bond area. The objective in structural bonding is to transfer and distribute stress and strain in such a way that the integrity of the structure is maintained. 

If we reverse the situation and bond two very flexible pieces of rubber together with a rigid, high modulus adhesive, a different picture emerges. The tensile strain 

In reality, all substrates and adhesives show some degree of elastic behaviour and so we have a situation where the stress levels within the adhesive layer are normally much higher towards the ends of the joint (Fig. 9). 

The finite element analysis technique has been used very successfully to confirm the regions of concentrated stress and strain. In this technique, the bonded assembly is subdivided into small elements and the forces relevant to each element are computed using basic mathematical equations. This is very useful, particularly in the understanding of complex joint designs. 

---

The loads acting on a bonded joint will result in various types of stresses. Stresses are normally expressed in N/mm. In the case of pure tensile and pure compressive loads the stress distribution over the bond line is very even, so that every part of the bond line carries the same load, and to calculate the stresses, the acting forces are simply divided by the bond area. In reality pure tensile and pure compressive loads are very rare and we are confronted more with shear, cleavage and peel loads. The joint stress distribution, i.e., the location of the stresses across the bond line, is less uniform and more complicated to calculate. 

Keywords— Finite element analysis. Total temporomandibular joint. Stress distribution. 

Flexibility is primarily characterized by a material s elongation. Flexibilizers in epoxy systems work by allowing the material to deform under stress. In this way stresses on the joint are distributed over a larger area. The flexibilized epoxy resin has the capability of compensating for differences in thermal expansion or elastic moduli of the substrates. 

In this study, residual thermal stresses were also eonsidered because co-cured lap joints generally undergo temperature drop (from 120D to 20D) during the curing process. The stress distributions in the co-cured single and double lap joints were analyzed using ABAQUS i.8 to be commercial finite element analysis software [21],... 

Fig. 8. Coordinate system of the co-cured single and double lap joints for calculating stress distributions in the ply-axis.

Fig. 10. Interfacial out-of-plane transverse stress distribution, a , of the co-cured single lap joint along the interface between steel and composite adherends. (a) [0]32t stacking sequence and (b) [ 45]4s s stacking sequence.

Fig. 11. Interfacial out-of-plane shear stress distribution, a , of the co-cured single lap joint...

Figures 12 and 13 show interfacial out-of-plane transverse and shear stress distributions of the co-cured double lap joints with [0]i6t and [ 45]4s stacking sequences along the interfaces between steel and composite adherends, respectively. It is important to consider interfacial out-of-plane shear stress rather than interfacial out-of-plane transverse stress because of the compressive stress distribution due to the symmetric configuration of the co-cured double lap...

Based on the failure mechanisms and stress distributions at the interface between steel and composite adherends of the co-cured single and double lap joints, tensile load bearing capacities of the two joints were evaluated. Since failure started at the edge of the interface between steel and composite adherends, it is important to consider the failure criterion using interfacial out-of-plane stress distributions at the interface. Three-dimensional Tsai-Wu and Ye-delamination failure criteria were used to predict partial cohesive failure or interlaminar delamination failure in the co-cured single and double lap joints. 

Takada, E et al. (1992) Study on the Differential Movement of External Wall in Building, Part 2 Stress Distribution at the Interface between Ceramic Tile Joint Mortar. Annual Convention of Architectural Institute of Japan, PP. 211-212. 

S. Tanaka and Y. Takahashi, "Effects of X-ray Beam Collimation on the Measurement of Residual Stress Distribution in a Si3N4/Steel Joint," ISIJ International, 30 [12] 1086-1091 (1990). 

The geometry of most adhesive joints appears deceptively simple, which has lead to some misleading design methodologies. The stress state and stress distribution in most adhesive joints... 

The lap shear fatigue test for the joints of the front cab module of the Maglev Transrapid TR08 has been analyzed by a fine detail analysis with 3D solid elements using the real cross-section geometry. The adherend materials are aluminum on one side and GRP on the other see also Section 32.5.1. The PU adhesive Sikaflex -254 Booster is modeled with the Ogden strain energy equation (Eq. (1), with N=2). The computed stiffness correlates well with the test results. The local stress distribution is visualized in Fig. 32.11. 

Visit plastics.bayer.com/plastics/emea/en/femsnap/index.jsp and examine the example snap-fit joint, noting the shape and stress distribution at maximum deflection. Find some examples of snap fit joints on consumer products and compare their design with that on the Bayer site. 

---