Glass/epoxy tensile strength ?

[Guillaume C.]

Hello, I have a hard time to find a proper value of tensile and compression strength of unidirectional fiberglass and epoxy resin.

FYI, this data is to be used for making dinghy davits. The beams will be made in wood and unidirectional fiberglass laid in grooves on the upper and lower surface of the beams.

I'm sure lots of you have those numbers laying around your desk! Thanks

 

[Guillaume C.]

Soooo.... If I got the concept right, this is the place to argue for countless pages on stupid projects, but where no one share info to actually do something, right?

Anyway, I'll do my scantling to what seem to be a fairly conservative 50ksi in tension with a safety factor of 5 considering all the weight on one davit. If anyone has better value, this would be the time to share as Ill do the glassing tomorrow

Cheers,
Guillaume

 

[groper]

1100Mpa in tension 900mpa in compression @ 55% fiber volume fraction - UD E-glass in epoxy matrix.

Modulus of Elasticity = 43/42Gpa tension/compression.

Source = Hexcel composites design guide.

 

[TANSL]

For small vessels has been written the ISO 12215 standard, which provides formulas to determine the mechanical properties of the laminates.
It is not easy, nor prudent, given a value, because the properties are highly dependent on the composition of layers has been applied, or % by weight of the fiber.
Not that we don´t want to share information with you but the question can not be answered with a number, if one want to be rigorous.

 

[groper]

Sure, but its hardly feasible to conduct coupon testing just do he can build some dingy davits... come on, how over regulated our thinking has become, thank god for litigation...

 

[TANSL]

groper, I don´t know if you know what I'm talking about. What I am saying is that there are formulas, very simple, giving completely appropriate values​​, and no recommendation that nobody knows where they came. Because the values ​​obtained in a project need not serve for another project built differently.
Is it difficult to apply this formula: compression ultimate tensile strength = 150 * FI + 72 N/mm2 ?
(FI = fiber content in% by weight)

 

[PAR]

I'm inclined to agree in as much as the information Guillaume C. is after is commonly available, either in terms of accepted engineering standards or the physical attributes of the various materials involved (fabric types, resin formulations, etc.). This said, following ISO or other standards would be a bit of over kill on some things, but in the case of a davit, I think a prerequisite. Davits have to tolerate tremendous loading at times and it's at these high load times, you'll really want the structure to retain it's shape and duty service.

The calculations for davits and their mounts, aren't especially complex and assuming a reasonable safety margin, not terribly difficult. I'm not sure of the value of unidi in wooden grooves for this application, but it might be possible to reduce some of the mass associated with a wooden davit, using this approach, if this is the goal of the engineering tactic (which isn't clear at this point). So, Guillaume, what are you trying to do, at least in regard to the unidi and wood interface? I do believe it's possible to incorporate what I'm picturing in my head (from you brief description), in this regard, but it would be more helpful if you provided some more detail and engineering goals.

 

[waikikin]

Soooo.... If I got the concept right, this is the place to argue for countless pages on stupid projects, but where no one share info to actually do something, right?

Anyway, I'll do my scantling to what seem to be a fairly conservative 50ksi in tension with a safety factor of 5 considering all the weight on one davit. If anyone has better value, this would be the time to share as Ill do the glassing tomorrow

Cheers,
Guillaume

Cheers Guillaume,
You started already
All the best from Jeff.

 

[TANSL]

Maybe I was wrong to interpret what was intended is to know whether the deck, GRP, will was able to support the stresses transmitted by the davit. If I was wrong, sorry.
On the other hand, if the aim is to make a GRP davit, I think it is not the most suitable material. But perhaps here too, I'm wrong.
A davit is just a beam or frame under certain loads and is so difficult to calculate as any other beam.

 

[SamSam]

Using the search term "proper value of tensile and compression strength of unidirectional fiberglass and epoxy resin" this came up.
You're figuring for straight down loads, have you figured for side loads as the boat gets slammed around and the dingy goes from side to side?

CYPLY® 1002 is a cured epoxy composite material based on a unique non-woven parallel filament construction. This type of construction minimizes filament stress abrasion that can shorten fatigue life in conventional reinforced plastics. CYPLY® 1002 uses type E continuous filament fiberglass.


Physical Properties Metric English Comments
Specific Gravity 1.85 g/cc 1.85 g/cc
Filler Content 64 % 64 %

Mechanical Properties Metric English Comments
Hardness, Barcol 70 70
Tensile Strength, Ultimate 20.0 MPa 2900 psi 90° stress angle
24.1 MPa 3500 psi 45° stress angle
965 MPa 140000 psi 0° stress angle
Tensile Modulus 9.65 GPa 1400 ksi 45° stress angle
9.65 GPa 1400 ksi 90° stress angle
39.3 GPa 5700 ksi 0° stress angle
Flexural Strength 75.8 MPa 11000 psi 90° stress angle
145 MPa 21000 psi 45° stress angle
1150 MPa 167000 psi 0° stress angle
Flexural Modulus 11.0 GPa 1600 ksi 90° stress angle
13.8 GPa 2000 ksi 45° stress angle
38.6 GPa 5600 ksi 0° stress angle
Compressive Strength 193 MPa 28000 psi 90° stress angle
241 MPa 35000 psi 45° stress angle
883 MPa 128000 psi 0° stress angle
Fatigue Strength 228 MPa
@# of Cycles 1.00e+8 33000 psi
@# of Cycles 1.00e+8 Flexural Fatigue (SN)
255 MPa
@# of Cycles 1.00e+7 37000 psi
@# of Cycles 1.00e+7 Flexural Fatigue (SN)
324 MPa
@# of Cycles 1.00e+6 47000 psi
@# of Cycles 1.00e+6 Flexural Fatigue (SN)
414 MPa
@# of Cycles 100000 60000 psi
@# of Cycles 100000 Flexural Fatigue (SN)
462 MPa
@# of Cycles 10000 67000 psi
@# of Cycles 10000 Flexural Fatigue (SN)
496 MPa
@# of Cycles 1000 72000 psi
@# of Cycles 1000 Flexural Fatigue (SN)
Shear Modulus 75.8 GPa 11000 ksi Short Beam; 0° stress angle; span/depth 5:1; ASTM D2344-76

http://www.matweb.com/search/datasheet.aspx?matguid=3f2253a553404b13893830617250b5d8&ckck=1

 

[Guillaume C.]

Hello, thanks for the answers so far

The goal is to make simple davits that will hold the 150 pounds inflatable and solar panel. The davits arms will be bolted trough the deck at their base but also rest on the stern rail so that the forces at the bases are not too great. Obviously the highest load point will be where the davits rest on the rail. The dinghy will be lifted 39" from the stern rail, and the davits are 3.5" thick at the rail.

I am using fiberglass laid in groove mostly because it is easy to make a groove of varying depth, then fill it with the fiberglass, then fair everything to be flush with the top surface. Applying the fiberglass directly over the core would be a bit more tricky to get a nice aesthetic curve with the varying thickness...

Side loads are not calculated as the dinghy will be lashed with diagonals when underway. (but there will be a carbon tube between the ends of the two davits to stiffen the assembly). Also wood is probably heavier than what is necessary for a core, but should handle the internals compression loads well, and is easier to get than high density foam!

Anyway, I was planning to route out the groove tonight so I have to settle on a value. As you can guest I'm no engineer, so any help you can provide is very welcome

 

[Guillaume C.]

Ive settled for a low 50ksi tensile with a safety factor of 7. In reality I've routed the groove 1/8" deeper than required and fill them a bit more than supposed.

Only problem so far, and this is the first time I laminate fiberglass so thick, is that I get some white spots in the layup. While playing with the fiberglass strands, they appears to be well wet but the resin is kind of creamy white. Should I be concerned with this?