The Analysis of Adhesively Bonded Advance Composite Joints using Joint Finite Elements.

The design and sizing of adhesively bonded joints has always been a major bottleneck in the design of composite vehicles. Dense finite element (FE) meshes are required to capture the full behavior of a joint numerically, but these dense meshes are impractical in vehicle-scale models where a course mesh is more desirable to make quick assessments and comparisons of different joint geometries. Analytical models are often helpful in sizing, but difficulties arise in coupling these models with full-vehicle FE models. Therefore, a joint FE was created which can be used within structural FE models to make quick assessments of bonded composite joints. The shape functions of the joint FE were found by solving the governing equations for a structural model for a joint. By analytically determining the shape functions of the joint FE, the complex joint behavior can be captured with very few elements. This joint FE was modified and used to consider adhesives with functionally graded material properties to reduce the peel stress concentrations located near adherend discontinuities. Several practical concerns impede the actual use of such adhesives. These include increased manufacturing complications, alterations to the grading due to adhesive flow during manufacturing, and whether changing the loading conditions significantly impact the effectiveness of the grading. An analytical study is conducted to address these three concerns. Furthermore, proof–of-concept testing is conducted to show the potential advantages of functionally graded adhesives. In this study, grading is achieved by strategically placing glass beads within the adhesive layer at different densities along the joint. Furthermore, the capability to model non-linear adhesive constitutive behavior with large rotations was developed, and progressive failure of the adhesive was modeled by re-meshing the joint as the adhesive fails. Results predicted using the joint FE was compared with experimental results for various joint configurations, including double cantilever beam and single lap joints.Ph.D.Aerospace EngineeringUniversity of Michigan, Horace H. Rackham School of Graduate Studieshttp://deepblue.lib.umich.edu/bitstream/2027.42/91417/1/sstaple_1.pd

Macroscopic Finite Element for a Single Lap Joint

Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/76219/1/AIAA-2009-2449-244.pd

Bonded Joint Elements for Structural Modeling and Failure Prediction

Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/90652/1/AIAA-2011-1719-934.pd

The Analysis of Adhesively Bonded Advanced Composite Joints Using Joint Finite Elements

The design and sizing of adhesively bonded joints has always been a major bottleneck in the design of composite vehicles. Dense finite element (FE) meshes are required to capture the full behavior of a joint numerically, but these dense meshes are impractical in vehicle-scale models where a course mesh is more desirable to make quick assessments and comparisons of different joint geometries. Analytical models are often helpful in sizing, but difficulties arise in coupling these models with full-vehicle FE models. Therefore, a joint FE was created which can be used within structural FE models to make quick assessments of bonded composite joints. The shape functions of the joint FE were found by solving the governing equations for a structural model for a joint. By analytically determining the shape functions of the joint FE, the complex joint behavior can be captured with very few elements. This joint FE was modified and used to consider adhesives with functionally graded material properties to reduce the peel stress concentrations located near adherend discontinuities. Several practical concerns impede the actual use of such adhesives. These include increased manufacturing complications, alterations to the grading due to adhesive flow during manufacturing, and whether changing the loading conditions significantly impact the effectiveness of the grading. An analytical study is conducted to address these three concerns. Furthermore, proof-of-concept testing is conducted to show the potential advantages of functionally graded adhesives. In this study, grading is achieved by strategically placing glass beads within the adhesive layer at different densities along the joint. Furthermore, the capability to model non-linear adhesive constitutive behavior with large rotations was developed, and progressive failure of the adhesive was modeled by re-meshing the joint as the adhesive fails. Results predicted using the joint FE was compared with experimental results for various joint configurations, including double cantilever beam and single lap joints

A new paradigm in functionally graded adhesives

To fully realize the benefits of advanced composites, mechanical fasteners must be supplanted by more efficient technologies such as adhesive bonding. The promise of functionally graded adhesives to provide particularly high levels of performance in this context has been recognized for decades, but a means of generating stable, high performance adhesive joints with arbitrary gradations in mechanical properties has proved elusive. Please click Additional Files below to see the full abstract

Functionally Graded Adhesives for Composite Joints

Adhesives with functionally graded material properties are being considered for use in adhesively bonded joints to reduce the peel stress concentrations located near adherend discontinuities. Several practical concerns impede the actual use of such adhesives. These include increased manufacturing complications, alterations to the grading due to adhesive flow during manufacturing, and whether changing the loading conditions significantly impact the effectiveness of the grading. An analytical study is conducted to address these three concerns. An enhanced joint finite element, which uses an analytical formulation to obtain exact shape functions, is used to model the joint. Furthermore, proof of concept testing is conducted to show the potential advantages of functionally graded adhesives. In this study, grading is achieved by strategically placing glass beads within the adhesive layer at different densities along the joint

New developments in dual cure epoxies

Direct write 3D printing provides an exciting new means of generating novel structures from thermosetting resins via an additive approach. Initial efforts along these lines demonstrated the preparation of homogenous, high quality parts. More recent work has shown that it is possible to modulate the properties of these parts locally through changes in orientation of high aspect ratio fillers. In this work, we present complementary developments related to resin chemistry that should provide practitioners of direct write 3D printing with additional options as far as the realization of functional gradations is concerned. This is accomplished via the creation of so-called “dual cure” resins. Here this term refers to materials that undergo thermal cure in a similar fashion to many conventional resins. Then, in a second step, the selective exposure of these materials to high energy radiation (gamma rays, electrons, etc.) results in further increases in local crosslink density, altering thermomechanical performance and providing a means of inducing arbitrary gradations in properties in a post-processing step. A number of different families of dual cure resins have been explored and are presented here, as well as data concerning changes in thermal and mechanical performance as a function of the details of the dual curing process. Preliminary efforts giving evidence of the generation of stable functional gradations in practice are also described. Ongoing and future efforts are focused on the optimization of these systems and the incorporation of their cure-dependent mechanical behavior into simulations in order to enable design optimization

Corotational Formulation for Bonded Joint Finite Elements

Peer Reviewedhttps://deepblue.lib.umich.edu/bitstream/2027.42/140672/1/1.j052422.pd

Applying systematic review search methods to the grey literature: a case study examining guidelines for school-based breakfast programs in Canada

Grey literature is an important source of information for large-scale review syntheses. However, there are many characteristics of grey literature that make it difficult to search systematically. Further, there is no ‘gold standard’ for rigorous systematic grey literature search methods and few resources on how to conduct this type of search. This paper describes systematic review search methods that were developed and applied to complete a case study systematic review of grey literature that examined guidelines for school-based breakfast programs in Canada. Methods: A grey literature search plan was developed to incorporate four different searching strategies: (1) grey literature databases, (2) customized Google search engines, (3) targeted websites, and (4) consultation with contact experts. These complementary strategies were used to minimize the risk of omitting relevant sources. Since abstracts are often unavailable in grey literature documents, items’ abstracts, executive summaries, or table of contents (whichever was available) were screened. Screening of publications’ full-text followed. Data were extracted on the organization, year published, who they were developed by, intended audience, goal/objectives of document, sources of evidence/resources cited, meals mentioned in the guidelines, and recommendations for program delivery. Results: The search strategies for identifying and screening publications for inclusion in the case study review was found to be manageable, comprehensive, and intuitive when applied in practice. The four search strategies of the grey literature search plan yielded 302 potentially relevant items for screening. Following the screening process, 15 publications that met all eligibility criteria remained and were included in the case study systematic review. The high-level findings of the case study systematic review are briefly described. Conclusions: This article demonstrated a feasible and seemingly robust method for applying systematic search strategies to identify web-based resources in the grey literature. The search strategy we developed and tested is amenable to adaptation to identify other types of grey literature from other disciplines and answering a wide range of research questions. This method should be further adapted and tested in future research syntheses