Simple methods for measuring tensile and shear bond strength and for determining elastic modulus and strength of coating

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Simple methods for measuring tensile and shear bond strength and for determining elastic modulus and strength of coating Yiwang Bao and Yanchun Zhou High-performance Ceramic Division Shenyang National Laboratory for Materials Science Institute of Metal Research, Chinese Academy of Sciences 72 Wenhua Road, Shenyang 110016, P. R. China ABSTRACT Two new testing techniques, one is for evaluating the ceramics-ceramics and metal-ceramics bond strength, and one is for determining the elastic modulus and fracture strength of brittle coating, were developed respectively. Tensile and shear bond strength were obtained by using compression load on a cross-bonded samples. Rectangular section specimens with surrounding coating or single face coating were used for evaluating the mechanical properties of brittle coating. Analytical formula for the modulus calculation of coatings was derived based on the mechanics of materials. Stress analysis of coated beam provides the expression of the critical stress to fracture in the coating layer. Experimental results confirmed the reliability and convenience of this simple technique. INTRODUCTION Understanding the bond strength between solid materials is significant for safe design and lifetime prediction [1,2]. Bond strength is also important for evaluating the properties of coating and glue [3,4]. Although the evaluation of bond strength exhibits increasing significance for the application of ceramic materials, general testing method for determining tensile bond strength has not been established to date. The strength and modulus are basic properties controlling the quality of coating in engineering application. The mechanical response of a homogenous sample with and without coating should be different in the bending test. From this difference, the properties of the coating should be deduced[5]. In order to deduce the modulus of coating from the change of bending stiffness, the mathematical relationship between the modulus and the change of stiffness must be derived. In the present study, two new testing methods are developed for providing a solution on the problems mentioned above. Experimental results indicate that these simple methods are feasible and accurate for evaluating the properties of ceramic joining and coating. MEASURING METHODS Evaluating bond strength by cross-bonded sample Cross-bonded samples were used to measure the bond strength. First the materials should be cut into bar samples with square cross-section and 4x4x20 mm3 in size, and all surfaces of the bar

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(a) for

(b)

Fig.1 Schematic diagram of cross-bonded sample, fixture configuration and loading form (a) measuring tensile bond strength and (b) measuring shear strength.

are polished and cleaned. Then each pair of bars that need to bond (sometimes is the same material) is joined to form a symmetrical cross. The approach used for joining, depends on the aims of measurement, can be any chemical or physical bonding. The measurement of tensile and shear bond strength can be performed by mounting the cros

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