Aluminium mast: crack or scratch?

[Pam Hoppenbouwers]

Hej, I would like to have your opinion about this situation.

Mast from a 20 year old Farrier F9 tri, rotating mast, length about 13 meter, setup from bottom to top: 1 m unstayed, 4,5 m stayed, spreader, 4,5 m stayed, connection front stay + back stays, 3 m unstayed to top, 5 cm bend over stayed 9 m, thickness aluminium: 3,7 mm

I removed the HMPE sailtrack and cracks?/scratches? now show mostly under it. In the process of making new laminate covered HMPE sailtrack, but not sure or the mast is OK. See pictures

• the crack/scratch is over most part of the mast, also the upper unstayed part
• only on one side of the original masttrack, in the corner of
• on some parts the surface is uneven at the different sides of the crack/ scratch
• searching on internet I was not able to find any pictures of identical situations
• I suppose compression and tension loads are more or less equal in aluminium so I can't explain why the backside
• Mast is not new but looks fine except 1 spot of pitting corrosion (20 mm2)
• Poured thinner over the crack/ scratch which runs of smoothly. Pushing a paper towel a few cm next to the pouring spot gets wet.

My question: is it a scratch and can I use the mast? Or is it a crack and do I have to find another one?

 

[Tops]

Hello Pam,
Those look like scratches in the anodized surface rather than cracks in the aluminum mast extrusion to me.
If someone has a better test method please reply.
I am curious how the covered sail track works, do you have a picture of the previous one installed?

 

[Pam Hoppenbouwers]

Hi Tops, thanks for your reply!

The masttrack was from Tides Marine: https://www.tidesmarine.com/product-category/track-slide-systems/. It had severe detoriation on the outside (mechanical and UV). The weak spot is the connection to the inner half round part of it only 3 mm wide. During the past years I drilled/ tapped/ bolted the parts that ripped. The masttrack itself is also quite loose in the mast.
So I decided to build a better version of it. 2 m sections with bolted slugs, HMPE (PE-1000) covered in 1 mm glasfiber. Glued together with 2 component PE glue PE-lijm - S-Polybond PEprofi 50ml https://www.s-polytec.nl/2k-pe-lijm-polyethyleen-klebstoff-spolybond-peprofi.html. Calculated the tension because of differences in thermal expansion coefficient and very well within spec of the polybond.
Now making a mold for glasfiber outside. A friend is making a milling tool for the T mill into the PE. See Pictures

 

[Tops]

Thanks Pam for the additional information. Do I understand correctly that the mast track and cloth will be glued to the mast?
Nice of your friend to make the tooling. At my work we do a similar operation for seating an o-ring with two passes, first is the access hole and the second is a cutter for the narrow section like these McMaster-Carr https://www.mcmaster.com/products/woodruff-keyseat-cutters/ .

 

[Barry]

Top Techniques Used in NDT for Aluminum Welding | Zetec https://www.zetec.com/blog/top-techniques-used-in-ndt-for-aluminum-welding/#:~:text=Nondestructive%20testing%20(NDT)%20for%20aluminum,and%20offer%20comprehensive%20probing%20measures.

Above is an article on non-destructive testing for aluminum. There are quite a few websites wrt aluminum NDT, worth checking out

 

[Barry]

Alternatively, you MIGHT be able to use a die penetrant kit. I did not mention this earlier because I considered that a scratch on the mast might capture some of the penetrant and falsely show
the same presentation as a crack.

 

[Pam Hoppenbouwers]

Thanks Barry, I did some reading and realized that I have to change my formulation of the question. So not "scratch or crack" but " how deep is the disturbance and what is happening inside".
Starting asking around for testers. Do you have practical experience with them?
ECT: could show there is an uncommon situation in conductivity, but possibly it is hard to get an objective remaining material thickness measurement from it as current in a cylindrical shape can go all directions so will flatten out the result?
UT: in the examples I see it is used in flat block situations. My situation is a curved outside and a non-flat inside so will give all kind of reflections? Might be possible to use an angled sensor.
Dye method: Can't give an indication about the depth of the disturbance.

 

[Pam Hoppenbouwers]

Do I understand correctly that the mast track and cloth will be glued to the mast?

Originally I wanted to use a slug/bolt system. Maybe I'm a bit old fashioned.. not to trust glue and prefer bolts . But glue might be not such a bad idea.. taking a part of the load of the aluminium.. would require a bit of extra calculating though.

McMaster cutters: interesting! I saw those kind of cutters while searching for a standard solution. What is your opinion on the best cutter and cutting conditions for PE-1000? height of the T is 3,2 mm, width is 22,4 mm.

 

[Tops]

Originally I wanted to use a slug/bolt system. Maybe I'm a bit old fashioned.. not to trust glue and prefer bolts . But glue might be not such a bad idea.. taking a part of the load of the aluminium.. would require a bit of extra calculating though.

McMaster cutters: interesting! I saw those kind of cutters while searching for a standard solution. What is your opinion on the best cutter and cutting conditions for PE-1000? height of the T is 3,2 mm, width is 22,4 mm.

I have to ask the machinists for feeds and speeds and cutter selection when I program for them, sorry I cannot answer directly.
https://www.plasticsintl.com/media/wysiwyg/Fabricating_and_Machining_UHMWPE.pdf
The short paper also discusses fastening towards the end.

 

[Barry]

I did some reading and realized that I have to change my formulation of the question. So not "scratch or crack" but " how deep is the disturbance and what is happening inside".
Starting asking around for testers. Do you have practical experience with them?

I was exposed to a flourescent penetrant process once. We manufactured fuel tanks for a customer who wanted the welds tested. We hired a guy to come in and check the couple of tanks.


Fluorescent penetrant inspection - Wikipedia https://en.wikipedia.org/wiki/Fluorescent_penetrant_inspection

Opinions, decisions and observations can be either right, wrong, or remain undetermined. I mention this as I am offering an opinion here and would be the thought process that I would have used to come
to my Opinion that these are surface scratches as compared to cracks that are deeper. Over the years we have repaired quite a few aluminum components that have had cracks.

Picture 1 of the mast cross section. The cross section is extruded and any area of the cross section does not appear to possess an area of stress concentration. Ie an area where I would think that a crack would
occur first. The track corners are pretty much radiused to minimize stress concentrations.

I would suspect that if it is a crack, the line of the crack would be in a relatively straight line along a fatigue line.
Picture 2 and 4, have straight lines near the area of the fillet on the inside of mast where the track profile "attaches" to the main mast. An indicator of a stress concentration here.
BUT
Picture 3, 4, 6 and 7 have scratches that do not lie along this "fault line" and are quite random
Picture 3, 4 and 7, thescratches vary quite far away from the "fault line" and parts are not in line
Picture 6 shows a return inflection point, ie a scratch that does not continue without interuption.
Picture 5 shows quite a few other "abrasion or scuff marks parallel to the scratch, leading me to believe that what ever caused the scuff marks caused the scratch marks.

So for these reasons I am leaning toward the fact that these are scratches not cracks

WRT your new factor, "

how deep is the disturbance and what is happening inside".

The dye penetrant can offer some idea of depth. The process is such that the dye will come back into a second of third layer of the applicated surface and if there is a lot of die on the surface, this die has to have
come from a deeper crack.

 

[Pam Hoppenbouwers]

As promised an update. The conclusion: scratch! Thanks all.