# Different Zero Strain Temps in an Assembly?

Question asked by 1-SII3UE on Jul 22, 2010
Latest reply on Jul 25, 2010 by 1-SII3UE

I'm trying to simulate an assembly where a top layer of silver is bonded to a bottom resin layer.  What I want to do is have the bottom resin layer be stress free at 90 C, and the bond coat and silver layer stress free at 25 C.  Is it possible to do this?

My assignment is below if any additional info is needed.  I completed questions 1 and 2, though my silver top coat is above the yeild stresses when at 180 C.  I don't know whether this is intended to happen or not, but question 3 is the one I'm stuck on.

ME 635: Modeling and Simulation

Case Study #1 (Must work individually).

Given:

• Geometry in the attached Solidworks      assembly file (Unitcell.sldasm)
• Material properties as      shown in Table 1.

Problem: Design a bond layer with appropriate properties such that the metallic coating adheres durably to a polymer resin or a polymeric matrix composite.

Assumptions and Constraints:

• No external loads or      constraints on the material. Only symmetry and periodic conditions. State      your assumptions.
• Components cannot  fail statically – All stresses must be      lower than failure stresses.
• Low Stress = High      Durability.
• Bond coat cannot be thicker      than top coat.

Deliverables:  A detailed report on the design process used for obtaining the solution and screen shots of key results. Clearly state all assumptions.   Your answers must be clearly identifiable in the report.

Question  I: Determine the modulus and thickness of the bond coat layer that maximizes durability for pure BMI  base substrate when the material operates at an elevated temperature of +180 0C  (Note: Set the properties of the cylindrical fiber same as that of the BMI resin). Assume that the coating, bond layer and the base are stress free at +25 0C.  Determine the mass percent added to the base substrate as bond and silver coating layers.

Question II: Determine the modulus and thickness of the bond coat that maximizes durability for a carbon fiber reinforced composite under the conditions stated in Case I.

Question III:  Using the bond layer as designed in Case II, if the composite (base substrate) is stress free at +90 oC  but both the bond layer and silver coating are applied (stress free state) at +25 0C

i)                    find the stress fields (6 components) when operating at  +25 0

ii)                   find the stress fields (6 components) when operating at  +180 0C

Table 1: Properties of the materials.

 Property BMI Carbon Fiber Bond Coat Layer Silver Top Coat Modulus (GPa) 4.6 230 ? 83 Poisson’s Ratio 0.35 0.3 0.3 0.38 CTE (a) x10-6 /oC 44 -0.41 30 18.9 Failure Stress (MPa) 103 3500 90 170 Density(gms/cc) 1.25 1.76 4 10.5

Figure 1: Geometry of the unit cell. Fiber is 10 mm in diameter. Cell has 50%
fiber volume fraction