QUESTIONS AND CONCERNS ANSWER.docx

Concern #1 - It appears that ERDC is looking for some extremely accurate parts that will pose some challenges from a molding standpoint. To make these parts we will have to mold small pieces by which we can somehow control the amount of resin richness in the fabric. Initially, we thought of compressing the mold as needed to control, yet that may become problematic since they are calling out for the first sample type to be 0.16” nominal thickness with a tolerance of +/- 0.016”. After reviewing a TDS sheet from Vectorply, their per lamina build is supposed to be 0.059”. If making a 3-layer section to target the 0.16” thickness, then that theoretically puts us at the 0.177” thickness which places us technically out of tolerance. This will be a very tight “landing zone” and things will only get more complicated once we start having to target different fiber volumes.

Answer #1 - Yes, these parts are intended for R&D purposes. We aim to gather publication-quality mechanical test data, and so we seek a higher degree of accuracy and QA/QC than a typical real-world component. The concern of the thickness tolerance is valid as this gives a narrow window to work with for traditional large component fabricators.

1. The process of meeting the geometric requirements is up to the fabricator’s discretion, however, the intent was for the specimens to be fabricated and then post machined to the desired size.

1. The ASTM standard that we are basing the sizing on requires a span to thickness ratio being the most important, as mentioned in the requirement. Therefore, the thickness can vary to accommodate the symmetric architecture requirement as well as the heavier fabric requirement if the appropriate span to thickness ratio is still met.

Concern #2 - In addition to this aspect, just hitting the fiber volumes within the allowed tolerance may be difficult. When we look at the 60% nominal fiber volume (we would usually expect to see around 57% give or take for a vacuum infused laminate section), using a fiber density of 2.6g/cm^3 and resin density of 1.07g/cm^3 and arbitrarily pick a small laminate with weights that make sense, I see the following:

- Molded laminate finished weight of 2,500g (5.51lbs) - would result from a part that is approximately 21.5625” x 21.5625” x 0.16” thick. If this has the nominal fiber volume of 60% (can be 58.5 – 61.5%), then there is a fiber content of 1961.8g (4.32lbs) and resin of 538.2g (1.19lbs)

- They are allowing us a +/-1.5% fiber volume ratio. This translates on the above part to allow the resin amount in the part (if the fiber going in is held constant) to vary from 2534.5g (5.59lbs) to 2467.2g (5.44lbs). This is a total window of 67.3g (0.15lbs), which is +/- 1.3% of the nominal weight. That seems tight even for a laminate. ----- We tried to look at the weights of some laminate parts we have in the shop currently that were water jetted, but the scales that can read their weight are not super precise. These were splice plates and they appeared as though they would have technically had too much variation in them for this project.

Answer #2 - We encourage prospective offerors to describe their ability to meet the requirements for controlling fiber volume fraction in terms of previous projects as part of the offer backup documentation.

Concern #3 - For the 45% fiber volume sample of this same thickness sample, we would have to nominally have 986.2g (2.17lbs) of resin in the part size discussed above. This means we will have to get 82% more resin into the same laminate. I do not know how achievable this will be, especially while holding the thickness requirement that is already problematic.

Answer #3 - See discussion of question #1 above. Offers may include proposed dimensions that will meet both the span to thickness ratio and the volume fraction requirements, in line with the offeror's typical manufacturing processes

Concern #4 – We noticed the callout of making the samples symmetric with regards to the fiber stack up orientation. This will not be achievable any time an odd number of layers are used. (See section 1.3, b). I think that this would be fine for the ¼” and ½” samples, but the 0.16” thick will have 3 layers, so it will not be doable.

Answer #4 - If wider tolerance is needed to achieve a symmetric laminate, then the bid must communicate the alternative approach to meet the requirement