Impact tests, bonded joints

ISO 11343, 1993, Adhesives—Determination of dynamic resistance to cleavage of high strength adhesive bonds under impact conditions- Wedge impact method The method is mainly aimed for the characterisation of metal substrates suitable for automotive applications. An instrumented impact testing machine (pendulum type) of 50-300 J and. 3-5.5ms maximum capacity is required for this test. A blunt wedge of approximately 1 mm tip radius and included angle of 8 is impact driven into a bonded joint at 3 ms" for aluminum alloy adherends and 2 ms" for steel adherends. The impact event should be... 

Adams RD, Harris JA (1996) A critical assessment of the block impact test for measuring the impact strength of adhesive bonds. Int J Adhes Adhes 16 61—71 AdamvaUi M, Parameswaran V (2008) Dynamic strength of adhesive single lap joints at high temperature. Int J Adhes Adhes 28 321-327... 

Adhesion Society. He is active in organising conferences and publishing and was a founder member of EURADH and WCARP, the main European and World series on Adhesion. He has been Joint Editor-in-Chief of the International Journal of Adhesion and Adhesives since 1999. His main research area is on adhesively bonded joints and he pioneered the application of finite element analysis for determining the stresses, strains, and strength of such joints. In addition to his adhesives research, he has also worked extensively on vibration properties in composites and developed low-velocity impact tests for non-destructively testing composites and sandwich structures. 

Standard test methods for the determination of impact resistance (ASTM D 950-82, ISO 9653 1998 and BS 5350, Part C4) specify the specimen geometry shown in Fig. 1, see also Appendix. While providing a simple basis for comparisons between adhesives, a number of disadvantages are associated with this configuration for example, it does not reproduce the differential strain effects often present in real joints and it does not readily permit the evaluation of bonds to many important coated substrates. 

Finite-element methods have also been used to evaluate new test equipment to measure shear strength under impact loads. In the equipment, two rectangular plates, bonded opposite faces of a vertical hexagonal prismatic rod, bear on a firm surface. The top of the central rod is subjected to an impact load. To prove the validity of the method, the maximum shear stress was compared with the impact shear strength, which was measured using a cylindrical butt joint subjected to impact torsional loads (see Tensile tests). 

This chapter will discuss the testing, analysis, and design of structural adhesive joints. Adhesive bond test techniques to be considered include tensile, shear, peel, impact, creep, and fatigue. Some considerations will also be given to the effect of environment and test rate. A continuum approach to the analysis of adhesive joints will discuss tensile, shear, and peel stresses which arise in various joint geometries. Classical theories by Volkersen, Goland and Reissner, and others will be included. References to finite element analysis will be made where appropriate throughout the chapter. 

For bonding, the important mechanical properties are principally E-modulus, elongation at break and viscoelastic behaviour. E-modulus governs the stiffness of the joint. Elongation at break is relevant for impact resistance and is measured after durability tests. Viscoelastic behaviour determines if creeping is expected in the application. 

Joints often experience impact or shock loads, and their reactions will differ depending on the rheology of the adherend and the adhesive. Another early standard is D-0950, Test Method for Impact Strength of Adhesive Bonds. It involves a relatively simple specimen (Fig. 17), but a special pendulum device is required for application of the impact shear load. 

Harris and Adams (1985) have examined the impact strength of lap-shear joints bonded with ductile adhesives. They also made open-ended cylinders of steel and aluminum alloy joined by spot welding and weldbonding with one of the ductile adhesives used for the lap-shear tests, and tested them under axial impact loading. The results indicated that the weldbonded joints had a small failure area and higher energy absorption than those joined only by spot welding. 

Variation in force and strain with time in a typical impact in the impact fatigue testing of a bonded lap joint (Casas-Rodriguez et al. 2007)... 

Under impact conditions, joints using this steel bonded with conventional toughened epoxy and acrylic adhesives fail preferentially at the zinc/steel interface, and this leads to an unacceptable impact performance. By testing a wide range of adhesives, it was found that the shear modulus had to be less than 100 MPa to enable the adhesive in the joint to deform sufficiently under impact to prevent the overstressing of the interface. 

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