General Adhesive Testing

Owned by Josh Dembicky
Last updated: Jul 30, 2021
3 min read

Details

  • LOCTITE EA E-120HP - pasted and compressed between the panel and chassis

    • Epoxy-based

  • Typical “Apply, Fix, and Cure” adhesive

Material Characteristics & Notes

  • LOCTITE EA E-120HP

    • Superior thermal shock resistance

    • Excellent mechanical and electrical properties

      • Specifically peel and impact forces

      • Suitable for low stress [I wonder if that will be a problem.]

    • Withstands exposure to a wide variety of solvents and chemicals

    • Bonds dissimilar materials including aluminum, steel, and other metals, as well as a variety of plastics and ceramics

      • No mention of metal to organic compounds however

        • From Technical Data Sheet (TDS):

          • Modulus of Elasticity (general epoxy resins) - ~4.5 GPa

          • Shear Modulus (general epoxy resins) - ~2.1 GPa

          • Average Tensile Strength - 41 GPa

          • Lap Shear Strength (Stainless Steel) - 23 GPa

Bonding Characteristics & Notes

  • Cavities may have been unfilled by the adhesive

    • Cavities created by part geometry or air bubbles created by uneven adhesive application

  • Clamped and cured for at least 24 hours

Known Forces or Stresses

  • General tensile and compressive stresses due to general usage

    • Specific overloaded substrates may cause excess strain and/or malformation

  • General weight of hanging parts (eg. bottom panel)

Potential Forces or Stresses

  • Any random stresses due to car functions (eg. the wheels being bumped into the bottom panel while turning)

  • Any random stresses due to the environment (eg. driving over a large rock the presses against the bottom panel)

Quality and/or Physical Concerns

  • Neither yet

    • The chassis hasn’t been adhered to anything yet, so no quality concerns

Test(s)

  1. Adhesive Yield Strength

    1. Determine how much the adhesive can withstand

    2. Tensile and shear stress must be tested

    3. Yield is different for application, so maybe just figure out when it crosses a certain elongation?

    4. Then find amount of force required

  2. General Weight

    1. Determine safety factor and actual elongation

    2. Needed: surface area, bottom panel mass

  3. Point Pressures

    1. Determine ratio strain between overloaded and general sections

  4. Quality

    1. Determine air bubbles?

    2. Determine shrinkage?

Testing Methods

  • MODS/Pre-calculations

[MAX ELONGATION AND DISPLACEMENT ARE BASED ON WHEN THE ADHESIVE BOND WOULD BREAK]

  1. Constant elastic and shear modulus, max elongation of 3 mm, assumed height is 2 mm, max horizontal displacement of 1 mm, constant SA (in mm^2)

    1. σ=Eε, σ=F/A, and ε=∆h/h

    2. τ=Gγ, τ=F/A, and γ=∆x/h

    3. Find F for both.

  2. Constant SA (in mm^2), gravity is rounded to 9.8 m/s^2, mass unknown, constant elastic modulus, assumed height is 2 mm, average tensile strength of epoxy given

    1. F=mg, σ=F/A, σ=Eε, and ε=∆h/h

    2. SF=σ_avg/σ

  3.  

  4. N/A

  • SW

  1. N/A

  2. FEA of weight

  3. N/A

  • Physical

  1. Test amount of force required for adhesive to yield directly

  2. Not needed.

  3. Physical examinations

Expectations

  • MODS/Pre-calculations

  1. I expect it to be a very large force needed in both cases

  2. I expect the change in height to be extremely minimal, and the safety factor to be incredibly high

  3. I don’t expect many air bubbles, but I expect a lot of missing edges

  • SW

  • Physical

Results

  • MODS/Pre-Calculations

  1. Approximate Yield Forces: 1.38 giganewtons and 0.284 giganewtons (tensile and shear respectively)

  2. Approximate Gravity-Induced Elongation: 0.241 nanometers

    1. Approximate Gravity-Based Safety Factor: 76 million

  3. N/A

  • SW

  • Physical

Analysis

  • MODS/Pre-Calculations

  1. The force required to dislodge the adhesive from the carbon fiber sandwich or the chassis bars is incredibly huge. This much was expected. Meaning that for this scenario to happen, something truly drastic would have to happen to the car.

  2. When sitting in place, the light bottom panel causes very little strain to the adhesive. The elongation seen isn’t even a nanometer. And in this scenario, the safety factor is almost 76 million!

  3. N/A

  • SW

  • Physical