Abstract Validation of an adhesive joint strength is by and large done through crack propagation analysis influenced by the loading modalities leading to diferent testing methodologies. The DCB test method is extensively used under more-1 loading to study the fracture and delamination toughness of adhesive joints. The significance and suitability of using the test when the hardener-resin proportion of the adhesive is varied needs to be scrutinized. Three mild steel DCB specimens were analysed incorporating the proportion-variation. The analysis revealed the need of using the Cohesive Zone Model (CZM) to study the crack propagation in all the specimens as a pattern of inconsistent proportionality emerged between the resin proportion and the crack propagation. The graphs converged to a particular degree between the experimental and the analytical realms which further instigated the need of modeling of the entire specimen inclusive of the adhesive layer through Finite Element Analysis. The obtained results provided insights on stress distribution inside the adhesive lay- er when crack propagation takes place in the specimens. The proportion variation done in a systematic manner is seen as a key factor in improvisation techniques for analysis when eforts are undertaken to introduce modalities in crack propagation direction control. Determination of Decisive Parameters in the Crack Propagation Analysis of an Adhesive Joint S. John Alexis 1 , P. Selva Kumar 2 and M. D. Mohan Gift 3* 1 Department of Automobile Engineering, Kumara Guru College of Technology, Coimbatore - 641006, Tamil Nadu, India; johnalexis@redifmail.com 2 Department of Mechanical Engineering, Paavai Engineering College, Namakkal - 637108, Tamil Nadu, India 3 Department of Mechanical Engineering, Panimalar Engineering College, Chennai - 600123, Tamil Nadu, India; mdgift@gmail.com Keywords: Adherent Material, Cohesive Zone Model, Double Cantilever Beam, Fracture Toughness, Hardener-Resin Proportion, Resistance Curves 1. Introduction Adhesive joints are identifed for their efective load and stress distribution over the total bonding region of the joint. Tey are considered over other conventional joints due to their abilities including fatigue elimination, crack stop- page, galvanic removal, vibration reduction, and enhanced sealing quality. Te justifcation of adhesive joints is done by studying the crack propagation during loading which needs the consideration of parameters including dissimilar adherent materials, adhesive composition, etc. Te study of crack propagation in an adhesive joint depends on the type of loading conditions in which the mode-1 loading is more prevalent. Hence an investigation is done to anal- yse the nature of crack propagation under mode-1 loading conditions using a Double Cantilever Beam (DCB) test. Composition variation is introduced in the specimens and the results are compiled. 2. Function of DCB Tests under Mode-1 Loading Te DCB test is used to study the fracture response of adhesive joints under mode-1 loading. Te main objective of the test is the calculation of the Strain Energy Release Rate (SERR) under mode-1 loading conditions. Fan 1 made use of this test to measure the fracture toughness of an adhesive joint between FRP adherents under mode-1 loading. Anderson T 2 also used a DCB test involving the analysis of the Cohesive nature of an Adhesive joint. Freed Y 3 applied the DCB test to study the crack formation of an Adhesive joint formed between laminated composite adherents. Te *Author for correspondence Indian Journal of Science and Technology, Vol 8(35), DOI: 10.17485/ijst/2015/v8i35/82822, December 2015 ISSN (Print) : 0974-6846 ISSN (Online) : 0974-5645