Tost Ring Failure

On Monday, June 5, 2017 at 7:45:05 PM UTC-6, Jock Proudfoot wrote:
Larry Morrow posted
Yesterday we found a toast ring with a fracture in the big ring. It
appears to completely through the ring. Has anyone else had this
experience? I have attached two image flies showing both sides of the
ring.
https://forum.sac.ca/download/file.php?id=254
https://forum.sac.ca/download/file.php?id=253

We had a TOST large ring failure while winch launching at a CAP Flight Academy a few years ago. It failed at the weld taper and the ring also broke opposite the weldment with the appearance of fatigue crystallization at the break. So, it's possible several launches were done with the failed weld before the ring failed at the second point. It was reported back to the vendor and also to TOST IIRC. Locally we discussed if perhaps some counterfeit supplies were getting into the channel. The academy leader passed away some time after the academy so I don't know the result of the report but perhaps the vendor will recall the event. I'll check.

Frank Whiteley

On Monday, June 5, 2017 at 9:44:32 PM UTC-6, Frank Whiteley wrote:
On Monday, June 5, 2017 at 7:45:05 PM UTC-6, Jock Proudfoot wrote:
Larry Morrow posted
Yesterday we found a toast ring with a fracture in the big ring. It
appears to completely through the ring. Has anyone else had this
experience? I have attached two image flies showing both sides of the
ring.
https://forum.sac.ca/download/file.php?id=254
https://forum.sac.ca/download/file.php?id=253

We had a TOST large ring failure while winch launching at a CAP Flight Academy a few years ago. It failed at the weld taper and the ring also broke opposite the weldment with the appearance of fatigue crystallization at the break. So, it's possible several launches were done with the failed weld before the ring failed at the second point. It was reported back to the vendor and also to TOST IIRC. Locally we discussed if perhaps some counterfeit supplies were getting into the channel. The academy leader passed away some time after the academy so I don't know the result of the report but perhaps the vendor will recall the event. I'll check.

Frank Whiteley

I'll amend my post to say that it was not evident that the failed ring was welded, but that separation had conical male/female shapes at the failure point. Looking for images in the archives, but nothing so far.

Frank Whiteley

Frank,

When there are "conical male/female shapes at the failure point" it generally indicates tensile overload failure (caused by exceeding the materials tensile strength). A giveaway would be necking on either side of these shapes, which might be what you're calling failure "at the weld taper".

Fatigue looks very different - the fracture surface shows a smaller smooth portion surrounding the origin, with the remainder of the fracture surface appearing granular (perhaps what you're calling calling "crystallization". Fatigue failure is caused by thousands, perhaps tens of thousands, of load variation in the presence of a small defect in the part (usually on the surface).

These are two completely different failure modes, and have two completely different causes. It would be interesting to see pictures of the actual failed ring and the fracture surface.

-John

On Tuesday, June 6, 2017 at 4:26:34 PM UTC-4, Frank Whiteley wrote:
We had a TOST large ring failure while winch launching at a CAP Flight Academy a few years ago. It failed at the weld taper and the ring also broke opposite the weldment with the appearance of fatigue crystallization at the break. So, it's possible several launches were done with the failed weld before the ring failed at the second point. It was reported back to the vendor and also to TOST IIRC. Locally we discussed if perhaps some counterfeit supplies were getting into the channel. The academy leader passed away some time after the academy so I don't know the result of the report but perhaps the vendor will recall the event. I'll check.

Frank Whiteley

I'll amend my post to say that it was not evident that the failed ring was welded, but that separation had conical male/female shapes at the failure point. Looking for images in the archives, but nothing so far.

Frank Whiteley

On Tuesday, June 6, 2017 at 2:51:26 PM UTC-6, John Carlyle wrote:
Frank,

When there are "conical male/female shapes at the failure point" it generally indicates tensile overload failure (caused by exceeding the materials tensile strength). A giveaway would be necking on either side of these shapes, which might be what you're calling failure "at the weld taper".

Fatigue looks very different - the fracture surface shows a smaller smooth portion surrounding the origin, with the remainder of the fracture surface appearing granular (perhaps what you're calling calling "crystallization".. Fatigue failure is caused by thousands, perhaps tens of thousands, of load variation in the presence of a small defect in the part (usually on the surface).

These are two completely different failure modes, and have two completely different causes. It would be interesting to see pictures of the actual failed ring and the fracture surface.

-John

On Tuesday, June 6, 2017 at 4:26:34 PM UTC-4, Frank Whiteley wrote:
We had a TOST large ring failure while winch launching at a CAP Flight Academy a few years ago. It failed at the weld taper and the ring also broke opposite the weldment with the appearance of fatigue crystallization at the break. So, it's possible several launches were done with the failed weld before the ring failed at the second point. It was reported back to the vendor and also to TOST IIRC. Locally we discussed if perhaps some counterfeit supplies were getting into the channel. The academy leader passed away some time after the academy so I don't know the result of the report but perhaps the vendor will recall the event. I'll check.

Frank Whiteley

I'll amend my post to say that it was not evident that the failed ring was welded, but that separation had conical male/female shapes at the failure point. Looking for images in the archives, but nothing so far.

Frank Whiteley

John,

I think you've described it accurately. Still checking around for images. They may not exist. This happened around 2009 and the rings certainly had not seen that many cycles. Not aware that anyone attempted to load test them, but who knows?

Thanks for your comments.

Frank Whiteley

I have personally seen 3 tost ring failures at my gliding club this season,
(the
last one only about 3 hours ago!) these were all the large rings on the
strops,
not the ring pair that goes to the release, unfortunately I have not been
able
to recover any of the rings to see the failure mode, however I was
examining
the rings on the other strops and found a couple that were obviously of
welded construction, and one was clearly oval rather than round, I don't
know
the age of them but they get very heavy use.
Ben.

At 03:16 07 June 2017, Frank Whiteley wrote:
On Tuesday, June 6, 2017 at 2:51:26 PM UTC-6, John Carlyle wrote:
Frank,
=20
When there are "conical male/female shapes at the failure point" it
gener=
ally indicates tensile overload failure (caused by exceeding the
materials
=
tensile strength). A giveaway would be necking on either side of these
shap=
es, which might be what you're calling failure "at the weld taper".=20
=20
Fatigue looks very different - the fracture surface shows a smaller
smoot=
h portion surrounding the origin, with the remainder of the fracture
surfac=
e appearing granular (perhaps what you're calling calling
"crystallization"=
.. Fatigue failure is caused by thousands, perhaps tens of thousands, of
loa=
d variation in the presence of a small defect in the part (usually on the
s=
urface).=20
=20
These are two completely different failure modes, and have two
completely=
different causes. It would be interesting to see pictures of the actual
fa=
iled ring and the fracture surface.=20
=20
-John =20
=20
On Tuesday, June 6, 2017 at 4:26:34 PM UTC-4, Frank Whiteley wrote:
We had a TOST large ring failure while winch launching at a CAP
Fligh=
t Academy a few years ago. It failed at the weld taper and the ring also
b=
roke opposite the weldment with the appearance of fatigue crystallization
a=
t the break. So, it's possible several launches were done with the
failed
=
weld before the ring failed at the second point. It was reported back to
t=
he vendor and also to TOST IIRC. Locally we discussed if perhaps some
coun=
terfeit supplies were getting into the channel. The academy leader
passed
=
away some time after the academy so I don't know the result of the report
b=
ut perhaps the vendor will recall the event. I'll check.
=20
Frank Whiteley
=20
I'll amend my post to say that it was not evident that the failed
ring
=
was welded, but that separation had conical male/female shapes at the
failu=
re point. Looking for images in the archives, but nothing so far.
=20
Frank Whiteley

John,

I think you've described it accurately. Still checking around for images.

=
They may not exist. This happened around 2009 and the rings certainly
had
=
not seen that many cycles. Not aware that anyone attempted to load test
th=
em, but who knows?

Thanks for your comments.

Frank Whiteley

On 11/06/2017 06:37, Benedict Smith wrote:
I have personally seen 3 tost ring failures at my gliding club this season,
(the
last one only about 3 hours ago!) these were all the large rings on the
strops,
not the ring pair that goes to the release,

The only TOST rings are the ones that go to the release. Any others are
from your club's local blacksmith shop.

Actual TOST ring failures are almost unheard of.

On Tuesday, June 6, 2017 at 9:16:37 PM UTC-6, Frank Whiteley wrote:
On Tuesday, June 6, 2017 at 2:51:26 PM UTC-6, John Carlyle wrote:
Frank,

When there are "conical male/female shapes at the failure point" it generally indicates tensile overload failure (caused by exceeding the materials tensile strength). A giveaway would be necking on either side of these shapes, which might be what you're calling failure "at the weld taper".

Fatigue looks very different - the fracture surface shows a smaller smooth portion surrounding the origin, with the remainder of the fracture surface appearing granular (perhaps what you're calling calling "crystallization". Fatigue failure is caused by thousands, perhaps tens of thousands, of load variation in the presence of a small defect in the part (usually on the surface).

These are two completely different failure modes, and have two completely different causes. It would be interesting to see pictures of the actual failed ring and the fracture surface.

-John

On Tuesday, June 6, 2017 at 4:26:34 PM UTC-4, Frank Whiteley wrote:
We had a TOST large ring failure while winch launching at a CAP Flight Academy a few years ago. It failed at the weld taper and the ring also broke opposite the weldment with the appearance of fatigue crystallization at the break. So, it's possible several launches were done with the failed weld before the ring failed at the second point. It was reported back to the vendor and also to TOST IIRC. Locally we discussed if perhaps some counterfeit supplies were getting into the channel. The academy leader passed away some time after the academy so I don't know the result of the report but perhaps the vendor will recall the event. I'll check.

Frank Whiteley

I'll amend my post to say that it was not evident that the failed ring was welded, but that separation had conical male/female shapes at the failure point. Looking for images in the archives, but nothing so far.

Frank Whiteley

John,

I think you've described it accurately. Still checking around for images. They may not exist. This happened around 2009 and the rings certainly had not seen that many cycles. Not aware that anyone attempted to load test them, but who knows?

Thanks for your comments.

Frank Whiteley

On reflection, the person who acquired the rings in question was an interesting character. I would not be surprised to find that he might have found a way to load test this set and perhaps unknowingly damaged them prior to putting them in use with the K-21's. As no report is known to have been filed, this secret may have died with him.

Frank W