Great points in your post (pun intended ;) )
The hammock material which failed was uncoated ripstop nylon. I was
using a standard sewing machine needle... not ball point, not
cutting needle, just sharp... When I made the bar tack, I had just
sewn dozens of feet of hook and also loop velcro, which tends to
cause burrs on the needle occasionally.
I believe that ripstop nylon would be less likely to be weakened by
sewing than silnylon is. The silicone stablizes the fabric thread
and may allow it to be cut by a needle when regular woven cloth
threads would be allowed to be separated by the needle.
For this reason, silnylon and tyvek may have some inherent weakness
for the weight supporting part of hammock making which the woven
ripstop does not.
I pointed out what I did to allow others to avoid over sewing the
velcro at such a vulnerable location. As Ed Speer noted, it is
likely the many needle punctures of the material which caused
weakness instead of strength.
--- In firstname.lastname@example.org, rosaleen43@a... wrote:
> Hi, Everyone!
> There have been several posts trying to study a failure in a
> starting at the point of a bar tack.
> Just to add points to consider in sewing. In my experience, there
seem to be
> materials that perform as if I'd just made perforations indicating
> want to be able to tear something off. Notably, stitching on
> foam/mylar for a reflector.
> There are likely a lot of reasons for this. Let me throw in one
> some of you who have less sewing experience. Manufacturers have
> with different needle points, targeting them to knits or wovens.
> also some sold as "universal point."
> So, along with length and diameter, dullness and burrs, we may also
> concern ourselves with the actual type of needle point. Before
> large project, or one that needs to bear weight, sew a test strip
> it to the forces you anticipate for you finished project. I
> enough silnylon to know, yet, it does best with the sharper needles
> wovens or the ball points meant for knits. It may just behave
> from what we expect.
> Cheers, and happy tinkering!