Mode II cohesive zone law of porous sintered silver joints with nickel coated multiwall carbon nanotube additive under ENF test

•An analytical solution is presented to extract the fracture energy of nickel coated multiwall carbon nanotube added sintered silver joints.•Comparisons of different methods on calculation of mode II fracture energy of nickel coated multiwall carbon nanotube added sintered silver joints are made.•Mode II cohesive zone model is presented for nickel coated multiwall carbon nanotube added sintered silver joints.•Porosity effect and thickness effect on mode II fracture energy are discussed for nickel coated multiwall carbon nanotube added sintered silver joints.•Strengthening mechanism of nickel coated multiwall carbon nanotubes in sintered silver is discussed. Various contents of nickel coated carbon nanotube added sintered silver joints are fabricated through mechanical alloying. An analytical method is presented to compute the fracture energy of ENF tests incorporating shearing effect and thickness effect, which shows better accuracy compared with traditional method, which are closer to the solutions of compliance based beam method. Mode II fracture energy, mode II fracture toughness and mode II cohesive zone model for different contents of nickel coated carbon nanotube added sintered silver joints are presented based on the data extraction of the ENF tests. With the increase of adhesive layer thickness, the fracture energy and the mode II fracture toughness improve. However, thickness effect is less significant but not negligible comparing with the strengthening effect on the improvement of fracture toughness, which is caused by adding nickel coated multiwall carbon nanotubes. The relation between mode II fracture toughness and porosity is also discussed. For most of the conditions, the mode II fracture toughness is higher than mode I fracture toughness regardless of additive content due to the crack deflection, crack bridging and pull-out mechanisms during the crack propagation except for those high content of additive whose fracture energy is reduced because of aggregation effect.