My research focuses on implementing novel techniques to characterize mechanical behavior and failure in advanced materials. Using simple metrologies based on fundamentals of fracture mechanics, I evaluate interfacial adhesion in multi-layer materials under stress states and environmental conditions relevant to their real-world applications. Such analyses are critical for assessing a material’s reliability in the field. Additionally, I couple mechanical testing with full-field deformation mapping to generate visual assessments of deformation and damage, from initiation through final failure.
Adhesion and Reliability of Photovoltaic Materials
Photovoltaic (PV) modules are designed for decades of sustained operation in the field. Over time, however, mechanical forces, moisture, and ultraviolet radiation degrade the adhesive properties of structural materials that protect the solar cell, ultimately leading to reduced performance. Through collaboration with the National Renewable Energy Laboratory, I am developing simple and reproducible metrologies for evaluating adhesion in PV encapsulation and backsheet structures, with the overarching objective of identifying key factors to improve reliability. Using these metrologies, I am characterizing adhesive properties of relevant layers of PV modules, in both coupon-level test specimens as well as on decades-old field modules.
In-situ evaluation of adhesion of encapsulation to glass and silicon in historic solar modules.
Adhesive Bonded Composite Joints
The weight of a composite structure may be greatly reduced through the use of adhesives rather than mechanical fixtures to connect individual components. Of particular concern is the toughness and reliability of an adhesively bonded joint under stresses and environmental forces during operation. Through collaboration with Boeing, I am investigating adhesion and environmentally assisted crack growth in adhesively bonded composite joints. In particular, I am investigating how various surface treatments can improve the robustness of an adhesive and how exposure to contaminants influences failure.
Influence of temperature and humidity on subcritical crack growth in adhesively bonded composite joint.
Full-field Deformation Mapping
Full-field deformation maps provide visual insight into damage initiation and failure in complex material systems. By coupling mechanical testing with digital image correlation (DIC), I quantitatively and qualitatively characterize relevant damage mechanisms in multi-layer structures, such as PV modules. When compared with stress-strain data, DIC is a valuable to for reconciling damage mechanisms (e.g. cracking in brittle layers, cohesive zone formation in tough layers) with mechanical performance.
2D strain field for titanium/glass/encapsulation double cantilever beam during delamination. Red localization encompasses the tip of the delamination front.
2D strain field of titanium-glass composite beam under 3 point bend. Red localizations indicated transverse cracking in the brittle glass layer.
Publications and Invited Presentations
- J. Tracy, A. Waas, S. Daly. A New Experimental Approach for In Situ Damage Assessment in Ceramic Matrix Composites at High Temperature. J. Am. Ceram. Soc., 98  1898-196, 2015.
- J. Tracy, A. Waas, S. Daly. Statistical Analysis of the Influence of Microstructure on Damage in Fibrous Ceramic Matrix Composites. Restricted Access. 2014.
- J. Tracy, A. Waas, S. Daly. Experimental Assessment of Fracture Toughness in Ceramic Matrix Composites Using the J-integral with Digital Image Correlation Part I: Methodology and Validation. J. Mater. Sci., 50, 4646-4658, 2015 (Cover Article).
- J. Tracy, A. Waas, S. Daly. Experimental Assessment of Fracture Toughness in Ceramic Matrix Composites Using the J-integral with Digital Image Correlation Part II: Application to SiC/SiC CMCs. J. Mater. Sci., 50, 4659-4671, 2015.
- J. Tracy, S. Daly, K. Sevener. Multi-Scale Damage Characterization in Continuous Fiber Matrix Composites Using Digital Image Correlation. J. Mater. Sci., 50, 5286-5299, 2015.
- J. Tracy and Daly S, Characterization of Fracture in CMCs at the Microstructural Length Scale, presented at the 38th Annual Conference on Composites, Materials and Structures, Cocoa Beach, FL (January 2014).
- J. Tracy and Daly S, Mechanisms of Deformation and Failure in CMCs at the Microstructural Length Scale, presented at the 37th Annual Conference on Composites, Materials and Structures, Cocoa Beach, FL (January 2013).
- Richard and Eleanor Towner Prize for Distinguished Academic Achievement (2013)
- Rackham Merit Fellowship (2009)