Compression or Tensile on Fiberglass

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Discussion Overview

The discussion revolves around the loading conditions on a fiberglass material subjected to compressive forces from an aluminum structure. Participants explore the implications of these forces on the fiberglass's tensile and compressive strength, particularly in the context of structural engineering principles and the applicability of established formulas.

Discussion Character

  • Homework-related
  • Technical explanation
  • Debate/contested

Main Points Raised

  • One participant questions whether the compressive force applied by the aluminum frame results in tensile stress on the fiberglass, suggesting that the load causes the fiberglass to stretch inwards.
  • Another participant clarifies that if the fiberglass panel is supported along its edges, the bending stresses would create tensile stress on the outer fibers and compressive stress on the inner fibers, similar to any plate under bending loads.
  • A participant expresses uncertainty about applying formulas from Roark's 'Stress and Strain' to composite materials, indicating a lack of confidence in using these resources for their specific problem.
  • Another participant seeks advice on using a specific case from Roark's for their loading condition, noting that they are new to structural engineering and looking for guidance on the application of the formulas.

Areas of Agreement / Disagreement

Participants express differing views on the nature of the stresses in the fiberglass due to the loading conditions. There is no consensus on the applicability of Roark's formulas to the composite material in question, and the discussion remains unresolved regarding the best approach to analyze the problem.

Contextual Notes

Participants highlight limitations in applying traditional metal plate formulas to composite materials, indicating potential gaps in assumptions and the need for specific conditions that may not be covered in existing literature.

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Homework Statement



A piece of aluminum as shown in the picture is applying a compressive force on the fiberglass material. I need to know if the loading material will exceed the specification of the fiberglass material.

sample.jpg



Homework Equations



Properties of fiberglass
Tensile strength Monolayer (Warp): 380 MPa
Tensile strength Monolayer (Weft): 300 MPa

Fiber Volume: 50%

Properties of resin
Tensile strength: 30 MPa

Volume: 50%


The Attempt at a Solution



My question is, since the loading structure is pressing against the fiberglass, the load will cause the fiberglass to be stretched inwards thus resulting in tension. Is this deduction reasonable?
 
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Is that an aluminum frame of sorts breing pressed upward against a fiberglass panel which is supported along its edges only? If so, the fiberglass bending streses are tensile on the outside fibers and compressive on the inside fibers, just like any plate subject to bending loads. Calculating those streses is quite difficult without a copy of Roarke's 'Stress and Strain' or computer finite element software.
 
Hi there,

I do have Roark's. But I am not so sure if it possible to apply those formulas meant for metal plates to my composite? I am quite lost actually. :(
 
Hi there,

I've included a picture of my loading condition. I've realized Roark does not provide any flat plate condition similar to that of my problem but I was wondering if it is possible to use Case no 8 in page 508 of Roark's?

I plan to take the outer dimension minus the inner dimension. Please advise as I am extremely new to structural engineering and I would gladly appreciate if someone could help me.

Thanks!
 

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