The static performance of lightweight multimaterial double lap joints is investigated in this study. Carbon-Fiber-Reinforced thermoplastic composite material is joined to Aluminum 6061 alloy via a combination of adhesive bonding and mechanical fastening. Adhesive-only joints are fabricated using epoxy-based and polyurethane-based structural adhesives. An M4-0.7 chrome-plated bolt is used for bolted-only samples, or in addition to polyurethane adhesive for hybrid bolted-and-bonded joints. Optimal bolt preload and tightening method are determined using computer-controlled torque-tension testing equipment. All geometric features, including the bolt hole, are waterjet-cut, and all joints are identical in shape and size, regardless of the joining method. The coupling surfaces are prepared by mechanical abrasion. The aluminum substrates are then ultrasonically cleaned in acetone, while the carbon fiber plates are manually wiped using compressed air and degreased using resin-friendly solvents. A controlled value of target surface roughness is achieved by repeated cycles of abrasion using several grits of sandpaper and is evaluated using an optical profilometer. The bonded joints are fabricated using a special fixture that allows to control adhesive thickness and length of overlap, while holding the coupons in place during the curing process in the oven.Cyclic corrosion testing of Double Lap joints is performed in accordance with a GMW 14872 3-stage laboratory standards for 30 one-full-day cycles. A complex salt solution is sprayed and nebulized in three hot and ambient temperature 8-hour stages per cycle. Three test DLJ’s are pulled out of the cyclic corrosion chamber for quasi-static lap shear testing after 1, 7, 14, 22, and 30 one-day corrosion cycles are completed.Bolted-only joints show a multi-stage progressive damage behavior, and failure is driven by the yielding of the substrates around the bolt hole. Progression of corrosion has insignificant effect on the static behavior of bolted-only joints. The performance of bonded-only joints is deteriorated by prolonged exposure to corrosion cycles, with the polyurethane-based adhesive joints retaining less than 15% of their original strength after 30 days in the chamber. Failure mode shifts gradually to the aluminum/adhesive interface with the advancement of corrosion. The results from hybrid bolted-and-bonded joints show two distinct failure stages. The adhesive alone carries the external loads in normal operating conditions. Once the adhesive fails, the bolt is engaged, and a great amount of energy is dissipated during the yielding of the joint. Corrosion cycles affect only the performance of the adhesive, although to a lower extent than in bonded-only joints. The total energy dissipation for hybrid bolted-and-bonded joints is not significantly lowered by exposure to corrosive environment. Results, observations, and conclusions are provided.

Effect of Cyclic Corrosion and Joining Method on the Strength of Multimaterial Double Lap Joints

Paper Proceedings: https://asmedigitalcollection.asme.org/IMECE/IMECE2021/volume/85543

ASME 2021 International Mechanical Engineering Congress and Exposition (IMECE2021)

Supporting the need among researchers worldwide for additional online and multimedia content, ASME now offers the ASME Conference Video Collection. This platform will collect and provide long-term access to conference presentation videos, encompassing all technology areas within ASME's technical conference and events program. About 30,000-40,000 engineers across all mechanical engineering and related disciplines participate in ASME conferences each year. This includes authors of approximately 6,000 to 8,000 technical papers published by ASME, the majority of whom also submit video presentations for our virtual conferences. The video collection will be available as an add-on to existing product packages or as a separate subscription.