Bathtub Wet Layup Solutions

Owned by Jens Dekker
Jul 29, 2023
4 min read

Problem: The layup for the aero shell (nickname bathtub) didn’t go according to plan and is partially infused. We need to get resin in the dry fabric to make a solid part, how is the question.

Criteria

Weighting

Solution #1

Solution #2

Solution #3

Solution #4

Solution #5

Criteria

Weighting

Solution #1

Solution #2

Solution #3

Solution #4

Solution #5

Solution

N/A

Proset INF 114 + 210

Proset INF 114 + 211

Proset INF 114 + 212

Solution 1,2,3 as re infusions

Use MGS 285/287

Work Time

1st

Wet layup + bag (60 minutes)

Wet layup + bag (110 minutes)

Wet layup + bag (4hrs)

 

Wet layup + bag (6 hrs)

Method

2nd

Wet Layup

Wet Layup

Wet Layup

Infusion

Wet Layup

Vac Time

5th

hold vacuum for 1 hr

hold vacuum for 10 hrs

hold vacuum for 18 hrs

 

vac not required (cure time 25 hrs, bag only needs to be present until gelation 8-10hrs)

Properties

3rd

8.7 GPa Tensile Strength

7.8 GPa Tensile Strength

8.0 GPa Tensile Strength

 

500 MPa Tensile Strength (70 MPa w/o carbon fiber)

Cost

4th

$900

$900

$900

$900

~$1200 (quote for $1100)

Procurement Time

2nd

1 Day

1 Day

1 Day

1 Day

5 Days

Notes

N/A

Same mix as first infusion

 

 

Same infusion again, but different lines

 

Criteria

Weighting

Solution #1
(Datum)

Solution #2

Solution #3

Solution #4.1

Solution #4.2

Solution #4.3

Solution #5

Criteria

Weighting

Solution #1
(Datum)

Solution #2

Solution #3

Solution #4.1

Solution #4.2

Solution #4.3

Solution #5

Solution

N/A

Proset INF 114 + 210

Proset INF 114 + 211

Proset INF 114 + 212

Proset INF 114 +

Proset INF 114 +

Proset INF 114 +

Use MGS 285/287

Work Time

(Time to Gel State)

5

0

1

2

0

1

2

3

Method

4

0

0

0

-1

-1

-1

0

Vac Time

1

0

-1

-2

0

-1

-2

0

Properties

3

0

0

0

0

0

0

-1

Cost

2

0

0

0

0

0

0

-1

Procurement Time

4

0

0

0

0

0

0

-1

Sum (with weighting)

 

0

4

8

-4

0

-4

6

Before a hard decision is made an additional discussion over mechanical strength is needed.

Since the two sets of resin would act as two separate bodies, the mechanical strength of the part is something to consider.

The green block is the resin hardened from the previous infusion.

The red would be what will be hardened after the second layup.

The concern is that the two would not act as a single substance, leading to the interface between the two different cured resin patches as a weak spot. It is not as weak as it is made out to be since the carbon fiber strands (black line) will connect the two sections.

The intended way to reinforce this would be to do another layup of kevlar on the inside of the car. This additional layer would be the blue block in the image below.

The horizontal interface between the blue and green as well as the blue and red creates a larger surface area to bond the different pieces, meaning the connection will be stronger. In the case that the strands between the red and green breaks, it will lead to the weakest the strands in the blue layer.

On second thought, considering the relative thickness of the red and green blocks, the force that will break the red and green interface, will certainly break the blue as it would have a smaller cross section. The forces may not be impacted greatly by the additional layer, however, there are no downsides to doing the 3rd layup other than time and cost. @Mohamed Goha your thoughts would be appreciated.

All cases would include this addition layup, however solution 5 extends to a 5.1 case and a 5.2 case.

This additional layup will be done using MGS 285/287.

For Solutions 1 through 4 each cost would add 1.2k for the resin.

Solution 5.1 would be two separate layups - cost double

Solution 5.2 would be a single lay up - bad for procurement (time would increase) plus cost doubles

The importance of cost does not change, and the relative scores would not change either

This means the best solution is Solution #3.

 

Now a quick outline of what the working schedule will be with everything we need to do.

Work Schedule

Tuesday -

  • take off bag (0.25 hrs) (6-8 people)

  • remove loose bits of infusion mesh (1 hr) (4 people)

  • make new bag (2.5 hrs) (Michael + Jaiden)

  • set the new bag on (0.5 hrs)

  • no spray tack needed

  • develop tools for wet laying the inside of the mold (0.5 hrs)

  • make a fourth structure around the nose (0.5 hrs)

  • get a smart plug

Wednesday to do the layup

  • Start mixing at 6pm

  • Extra equipment

    • 2 boxes of gloves

    • More paintbrushes

    • Cut the aluminum tubes

  • 4 hours before gel state

  • 1.5 hrs for wet layup (Michael, Jaiden, Jasmine, ~Nathan, ~Emily, ~Jens, ~Malcolm, ~Katherine)

  • set the outlets (0.25 hrs)

  • closing the bag (1 hr)

  • set the structures to prevent the mold from flexing (0.25 hrs)

Sometime on the 16th or 17th do the additional layup