Peel joints stresses

D 2918 Practice for Determining Durability of Adhesive Joints Stressed in Peel... 

Subjected to stress, moisture and temperature uses peel joint As above, but uses single-lap shear joint loaded in tension As above but uses a wedge test Exposure to moisture and temperature... 

Most theoretical analyses have been carried out on single or double lap joints, which are the primary types of joints used for determining the strength of adhesives. Properly designed joints stress the adhesive in shear. Adhesives are especially weak in peel, and are also weak under tensile loads applied normal to the plane of the joint. The earliest theoretical lap-joint work involved simplifying assumptions that (1) the joint was a... 

ASTM D2918-99 Standard practice for determining durability of adhesive joints stressed in peel. 

ASTM D 1828-70—Atmospheric exposure of adhesive-bonded joints and structures Determining durability of adhesive joints stressed in peel -Determining durability of adhesive joints stressed in shear by... 

Figure 2 shows schematic diagrams of some good and poor joint designs related to the preceding comments. It can clearly be seen that the major difference between good and poor is to restrict peel-cleavage stress of the joint. 

The investment needed in terms of cost and time means that few such comprehensive programmes are undertaken in the short-term culture of contemporary industry. Still important are classic reports of such weathering trials undertaken by UK government laboratories. These involved bonded aluminium double overlap joints, stressed and unstressed, peel and honeycomb specimens (see Peel tests). These were exposed at the Royal Aircraft Establishment (RAE), Famborongh (temperate), and at the Joint Tropical Research Unit (JTRU) sites at hmisfail (hot-wet) and Cloncurry (hot-dry), Aushalia. Periods of up to 6 years were employed, exposing a variety of adhesive systems to the different climates. 

Atmospheric Exposure of Adhesive-Bonded Joints and Structures. Practice for (D1828) Determining Durahility of Adhesive Joints Stressed in Peel, Practice for (D 2918) Determining Durability of Adhesive Joints Stressed in Shear by Ihnsion Loading, Practice for (D 2919)... 

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. 

G. F. Carter, Durability of adhesive peel joints while stressed in water, ASTM STP 401, p. 28 (August 1966). 

Method for assessing the effect of stress and moisture and temperature uses a peel joint test... 

Dom and Liu (1993) investigated the influence of the spew fillet in plastic/metal joints. The study includes an FE analysis and experimental tests and they conclude that the spew fillet reduces the peak shear and peel adhesive stresses and decreases stress and strain concentrations in the adherends in the most critical regions. They also studied the influence of different adhesive and different metal adherends. A ductile adhesive and a more balanced joint (aluminum/plastic instead of steel/plastic) give a better stress distribution. 

The causes of poor adhesion in SBR rubber soles are quite diverse. Overvulcanized layer are too stiff to support peel strength stresses. Presence of silicone release agents may reduce the bond strength of SBR rubber sole joints. The presence of antiadherend moieties on their surfaces, their low surface energy, and the migration of low-molecular moieties (antiozonant wax, processing oils) to the interface once the adhesive joint is produced are other causes for the lack of adhesion in SBR rubber. 

The peel/shear stress eoneentration is the principal reason to cause the catastrophic failure of adhesively bonded joints. Many traditional enhancement methods have been developed to mechanically improve the joint strength. Comparing to these traditional mechanical enhancement methods, a smart strength improvement concqrt for adhesive joint has been introduced to ad tively realize the reduction of peel/shear stress concentration by the inte ated piezoelectric layers. Here, the current development of adhesively bonded smart joint systems is review and summarized in d ail. 

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