Modal Analysis of Square Aluminum Bar with Attached Pillars: Glued vs. Solid Structure Debate

Question:

In our group's research project, we are conducting a modal analysis on a square aluminum bar with small pillars attached to the top. Each unit cell consists of a 6x6x6 cm base cube and a 1.5x1.5x3 cm pillar, with over 15 unit cells in our model. Due to budget and time constraints, we are deliberating whether to glue the pillars to the bar or invest in creating a solid piece. Our main concern is whether the Frequency Response Function (FRF) graphs obtained from a glued structure will be sufficiently accurate compared to those from a solid piece in our modal analysis. We are focused on identifying band gaps within specific frequency ranges, ranging from 10 to 8000 Hz. Our objective is to test a theory and establish baseline results, with the aim of securing funding for a precise solid model in the future. Your insights would greatly assist in resolving this debate as we work towards achieving our research goals. Thank you for any support you can provide.

Top Replies

It may seem improbable, but is it possible to ensure that the elastic modulus of the adhesive joint compares to that of the metal? Do you have any evidence to support this assertion?

I fully concur with Testtech's perspective. When analyzing a structure in three dimensions as a network of interconnected mass-spring components, the disparity in stiffness between glue and metal elements becomes evident. Consequently, the modal characteristics are expected to vary as well. To validate this theory, a simple modal test can be conducted on a metal rod; subsequently, the rod can be segmented, glued back together with a high-strength adhesive such as locktite, and retested. Anticipate a substantial disparity in the results.

From my experience in similar projects, it seems gluing should suffice for establishing initial results, especially considering your budget and time limitations. Gluing might slightly alter the FRF, but the changes should not be drastic. It only becomes more of a concern when you're measuring vibration modes in very high frequency ranges, where the adhesive layer could significantly affect stiffness. If your primary objective is to establish a baseline and secure funding for a more precise solid model in the future, I believe a glued setup would adequately serve your purpose and help to validate your theory. Just ensure you use industrial strength adhesives rated for metal bonding and consider the adhesive's properties on the FRFs, too.

Considering your objectives and constraints, I'd suggest starting with the glued structure for now. Glued models have been used effectively in many preliminary modal studies, and could provide reasonably accurate FRF graphs that reveal significant band gaps in your specified frequency ranges. The accuracy might not be as high as with a solid piece, but it should be enough to establish baseline results and test your theory. This would enable you to present initial findings to secure future funding for a more accurate solid model. As long as you duly acknowledge any potential limitations of the glued-structure approach when presenting results, I believe this could be a reasonable and cost-effective starting point for your project.

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Frequently Asked Questions (FAQ)

FAQ: 1. What is the purpose of conducting a modal analysis on the square aluminum bar with attached pillars?

Answer: - The purpose is to identify band gaps within specific frequency ranges, ranging from 10 to 8000 Hz, as part of testing a theory and establishing baseline results for future funding.

FAQ: 2. What are the dimensions of the base cube and pillar units in the model?

Answer: - Each unit cell consists of a 6x6x6 cm base cube and a 1.5x1.5x3 cm pillar.

FAQ: 3. What are the considerations when deciding whether to glue the pillars to the bar or create a solid piece for the modal analysis?

Answer: - The main considerations are budget and time constraints, as well as the accuracy of Frequency Response Function (FRF) graphs obtained from a glued structure compared to those from a solid piece.

FAQ: 4. How many unit cells are included in the model being analyzed?

Answer: - There are over 15 unit cells in the model being analyzed.

FAQ: 5. How can insights from the debate between using a glued structure versus a solid piece help in achieving the research goals?

Answer: - Insights from this debate can help in resolving the accuracy concerns and guide the decision-making process towards achieving the research goals effectively.

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