A Viscoelastic-Plastic Approach to Static Strength Prediction of Bonded Joints
Abstract
Adhesively bonded joints to connect structural components of U.S. Navy aircraft and vessels are not yet widely used despite their many benefits. Reliable adhesively bonded joints with no metal fasteners would reduce these assets weight and their manufacturing and operational costs. However, widespread use of adhesive joints is hampered by the current inability to predicttheir static strength. Consequently, mechanical jointsknown to produce stress concentration regions, moisture ingress areas, and increased structural weightare most commonly used. Thus, industry and the U.S. Department of the Navy demands for lower structural weights and reduced part counts on their assets are competing with certification authorities need to meet high safetystandards. These authorities require a physics-based approach to predict the static strength, durability, and life of these critical joints. As a result, new models capable of predicting time to failure for adhesively bonded joints are needed. In addition to the ability to monitor in situ adhesive joints, using a holistic perspective enables new model development that account for the differentparameters affecting the static strength oly, mechanical joints in the aeronautical industry follow a damage tolerance approach, as no standards are available for bonded or hybrid joints. An advisory circular by the FAA indicates that the limit load capacity needs to be proven by: (a) analysis, tests, or joint [1]. However, all static strength predictions of bonded joints exclude the long-term effects of any changes to the adhesive and adherends composing the joint. Therefore, to produce more accurate and reliable prediction models, visco-elastic-plastic (VEP) and stressrelaxation models should be incorporated into in situ NDI (this last one, is commonly known as structural health monitoring (SHM)). Data from SHM would feed into the physics-based VEP model to update the predicted estimates. The challenge of static strength and life assessment predictions lies in the variability of multiple parameters (e.g., loads, initial structural conditions, material aging, and environmental effects) affecting these joints. All of these factors can interact,further complicating efforts to assess degradation and determine the useful structural strength remaining. Connecting NDI measurement techniques with VEP models will mitigate this challenge while providing invaluable data sets to determine the underlying physics at play within these resin/joint systems.This proposed project aims to develop a static-strength prediction model that incorporates both analytical and computational m the resin and determination of visco-plasticity, creep compliance, and stress relaxation effects using available standards; (ii) residual stress determination using the latest generation of sensing technology; (iii)analytical and computational analysis through the development of a Cohesive Zone Model that allows for crack retardation and VEP effects, (iv) parameters estimation using Bayesian negative binomial regressions minimizing the uncertainty followed by (v) in situ verification and validation of the static strength models prediction using experimental mechanics techniques.The ability to predict the static strength of a bonded joint with a high level of confidence will achieve a major milestone demanded by the certification authorities such as the FAA and the Department of the Navy. Finally, data obtained will provide the scientific community a better understanding of adhesive joint failure and correlation of how these parameters affect the staticstrength and life of adhesively bonded structures.
Document Details
- Document Type
- DoD Grant Award
- Publication Date
- Feb 02, 2021
- Source ID
- N000142112057
Entities
People
- Marcias Martinez
Organizations
- Clarkson University
- Office of Naval Research
- United States Navy