Prototyping during race season, yay or nay?

chamaedorea.elegans wrote:

Naw, it’s a fundamentally flawed design and manufacturing process (in terms of composites engineering), from what I can see from their prototype manufacturing pictures, as well...

Naw, it’s a fundamentally flawed design and manufacturing process (in terms of composites engineering), from what I can see from their prototype manufacturing pictures, as well as from Kerr’s broken frame pictures — in my opinion. Also, the fact that something is a prototype doesn’t mean that it’s permissible to utilize a dangerously designed / engineered / manufactured product, which could result in the substantial impairment or death of an athlete.  

The first flaw is the straight-insertion of the top tube AND the down tube into the lug, at the same draw angle. As such, if the bond isn’t perfect and the bondline fractures, the tubes are not mechanically constrained by different draw angles...both tubes pull out of the lug(s) in the exact same draw direction — that is a serious design / engineering flaw in my professional (composites engineering) opinion. If designed differently, with different draw angles for each tube / lug, both tubes likely would not experience the same stress vectors at the bondine (due to their varying orientation) and thus both bondlines likely wouldn’t fail at the same time. And both tubes would not (and could not) pull out of the lug(s) at the same time, in the same direction. With different draw angles / bondline orientation / stress vectors, one bondline would likely fail before the other, allowing detection of the bond failure. Likewise, the different draw angles (if the tube are stiff & strong enough) wouldn’t allow both tubes to pull out at the same time, in the same direction. Atherton got that right. Pivot got that wrong. It was a major oversight and a fundamental engineering flaw, in my opinion. That Pivot frame even has a separate individual top tube, and a separate individual down tube — so they didn’t need to utilize the same draw angle for both the top tube & down tube. (But the same draw angle would be required if the rest of front triangle was a single-piece composite molding and the top and down tubes weren’t separate pieces).  

Also, if the bondline wasn’t perfect, bonding failures can occur from bonding adhesive microcracking, adhesive macro-cracking, and incomplete adhesive coverage. Galvanic corrosion, and other corrosion, can be an issue with aluminum lugs and carbon fiber (unless the carbon fiber is insulated with fiberglass or similar non-conductive material). Aerospace companies often use fiberglass layers to prevent galvanic corrosion, making sure to not sand them off, nor sand too deeply into the fiberglass, where it bonds to aluminum. Likewise, at a minimum, they’ll typically hard anodize the aluminum, or use another bonding-optimized mil-spec surface preparation or treatment and/or anodizing process. Often, aerospace companies apply a military-spec type of cured epoxy primer onto the aluminum, to which the subsequent prepreg composite, or bonding adhesive, can tenaciously bond (and bond without corrosion due to the protective anti-corrosion epoxy coating). It appears Pivot excluded some or all of these critical (and fairly simple) steps. I also don’t see any fiberglass on the cured tubes, in the bonding area, in the prototype manufacturing pictures that Pivot released for publication on Pinkbike — it appears to be solely a woven carbon fiber surface layer, with no galvanic insulation layer, in the area bonded to the lug.

Additionally, it appears the bonding process was flawed — I didn’t seem to see much adhesive on the composite nor aluminum portions of the failed bond (in Kerr’s broken frame pictures). There’s a chance they didn’t properly remove mold release on the cured composite tubes. Or that they didn’t properly prepare the composite & aluminum surfaces (via abrasion and solvent cleaning), or that insufficient bonding adhesive was used, or that the adhesive scraped out of place during the assembly process...thus resulting in insufficient adhesive in the area to be bonded. The bonding process also appears suspect, from what I’ve seen in various pictures of the frame & manufacturing process. Trek (OCLV) and others co-mold several 0.002” tall “pips” around the circumference and length of their “male” bonded tubes...those pips center the tube into the female lug (or tube) and ensure an optimal 0.002” thick bondline, and it ensures that the adhesive doesn’t get scraped out of place as the tube is inserted. I doubt Pivot did anything like those 2-thou pips, based on several of my observations. It’s also usually a good idea to “inject” a bit of structural epoxy bonding adhesive into a port at the bonded joint, after initial assembly with adhesive, to ensure the entire bondline is fully covered, saturated, and void-free. I don’t see that sort of adhesive-injection port feature on their frame (from my cursory review), but I think Specialized might do that on their prototype DH frames. I think Atherton does the same. It’s common in aerospace, F1, and even in the production of certain composite sports cars. I actually import special 3M structural adhesive from the UK (it’s what I used on McLaren’s carbon fiber “tubs” and Bentley Motors’ prototype carbon fiber doors for one of their Super Sports technology demonstrator cars) which is better than what’s available in the US (likely because it’s more toxic =) — it’s strong, and has superior mechanical & dynamic performance numbers, and is highly toughened (as well as being highly crosslinked for extra strength, if you post-cure it a bit around 250F to 350F after achieving initial bond strength at room temp, overnight. Engineers, prototype manufacturing technicians, and production manufacturing technicians, cannot mess around with bond failures — it has to be done right, and the materials and manufacturing processes have to enable bonding perfection. Every time. 

Also, Pivot appears to use cast-silicone custom bladders for their prototypes — and silicone / silicone oil can readily leach into the prepreg (unless significant protective countermeasures are taken). The silicone contamination can greatly adversely affecting bonding / adhesion. Aerospace companies ban everything silicone in their composites manufacturing facilities, for this reason. Even those yellow silicone “Livestrong” Lance Armstrong bracelets are strictly banned. Pivot’s custom composite tubes could have been contaminated with silicone that could affect their adhesive-bond performance — and their manufacturing pictures show the silicone bladder directly in contact with the uncured & cured carbon fiber prepreg, directly adjacent to the end of the tube (where the composite tube is subsequently bonded). Polyurethane, latex, molded nylon, or nylon film over polystyrene foam rigidized-bladder mandrels, are good alternatives for prototypes (and sometimes production).  

Lastly, the kink / bend in the carbon fiber downtube, just behind the lug, will put both sides of the downtube in compression right at the kink / downtube bend...and carbon fiber fails in compression. Although Kerr’s bike didn’t fail there, it’s a suboptimal compression-loading scenario which will result in pronounced compressive forces in the laminate on both the top and bottom sides of the downtube at the bend (in a jump-case loading scenario like Kerr experienced). Frames have to be engineered, in every way, for those worst-case cases...and engineering a frame with a tube geometrical configuration that results in substantial compressive forces on both sides of a composite tube is just questionable engineering, in my opinion. The goal should be to limit inducing those sort of compressive loads and mitigate the risk of composite compressive failure.

-WRCDH 

 

aka Pivot bikes, BIG TRASH 

dknapton wrote:

Writing multiple paragraphs over a couple blurry screen grabs and followong it up with Pivot is trash leads me to believe you might be a little...

Writing multiple paragraphs over a couple blurry screen grabs and followong it up with Pivot is trash leads me to believe you might be a little biased and can't be taken too seriously. 

LePigPen wrote:

https://youtu.be/j2UqzYQ_Qjc?feature=shared&t=656 Timestamped 11 minutes in... BK punts his front end into a tree during praccy   edit: around 13:37 he looks down at the bike... oh...

https://youtu.be/j2UqzYQ_Qjc?feature=shared&t=656

Timestamped 11 minutes in... BK punts his front end into a tree during praccy

 

edit: around 13:37 he looks down at the bike... oh my god he skips the entire end section while looking down at the bike... but theres no talking it just goes to the next run

chamaedorea.elegans wrote:

Naw, it’s a fundamentally flawed design and manufacturing process (in terms of composites engineering), from what I can see from their prototype manufacturing pictures, as well...

Naw, it’s a fundamentally flawed design and manufacturing process (in terms of composites engineering), from what I can see from their prototype manufacturing pictures, as well as from Kerr’s broken frame pictures — in my opinion. Also, the fact that something is a prototype doesn’t mean that it’s permissible to utilize a dangerously designed / engineered / manufactured product, which could result in the substantial impairment or death of an athlete.  

The first flaw is the straight-insertion of the top tube AND the down tube into the lug, at the same draw angle. As such, if the bond isn’t perfect and the bondline fractures, the tubes are not mechanically constrained by different draw angles...both tubes pull out of the lug(s) in the exact same draw direction — that is a serious design / engineering flaw in my professional (composites engineering) opinion. If designed differently, with different draw angles for each tube / lug, both tubes likely would not experience the same stress vectors at the bondine (due to their varying orientation) and thus both bondlines likely wouldn’t fail at the same time. And both tubes would not (and could not) pull out of the lug(s) at the same time, in the same direction. With different draw angles / bondline orientation / stress vectors, one bondline would likely fail before the other, allowing detection of the bond failure. Likewise, the different draw angles (if the tube are stiff & strong enough) wouldn’t allow both tubes to pull out at the same time, in the same direction. Atherton got that right. Pivot got that wrong. It was a major oversight and a fundamental engineering flaw, in my opinion. That Pivot frame even has a separate individual top tube, and a separate individual down tube — so they didn’t need to utilize the same draw angle for both the top tube & down tube. (But the same draw angle would be required if the rest of front triangle was a single-piece composite molding and the top and down tubes weren’t separate pieces).  

Also, if the bondline wasn’t perfect, bonding failures can occur from bonding adhesive microcracking, adhesive macro-cracking, and incomplete adhesive coverage. Galvanic corrosion, and other corrosion, can be an issue with aluminum lugs and carbon fiber (unless the carbon fiber is insulated with fiberglass or similar non-conductive material). Aerospace companies often use fiberglass layers to prevent galvanic corrosion, making sure to not sand them off, nor sand too deeply into the fiberglass, where it bonds to aluminum. Likewise, at a minimum, they’ll typically hard anodize the aluminum, or use another bonding-optimized mil-spec surface preparation or treatment and/or anodizing process. Often, aerospace companies apply a military-spec type of cured epoxy primer onto the aluminum, to which the subsequent prepreg composite, or bonding adhesive, can tenaciously bond (and bond without corrosion due to the protective anti-corrosion epoxy coating). It appears Pivot excluded some or all of these critical (and fairly simple) steps. I also don’t see any fiberglass on the cured tubes, in the bonding area, in the prototype manufacturing pictures that Pivot released for publication on Pinkbike — it appears to be solely a woven carbon fiber surface layer, with no galvanic insulation layer, in the area bonded to the lug.

Additionally, it appears the bonding process was flawed — I didn’t seem to see much adhesive on the composite nor aluminum portions of the failed bond (in Kerr’s broken frame pictures). There’s a chance they didn’t properly remove mold release on the cured composite tubes. Or that they didn’t properly prepare the composite & aluminum surfaces (via abrasion and solvent cleaning), or that insufficient bonding adhesive was used, or that the adhesive scraped out of place during the assembly process...thus resulting in insufficient adhesive in the area to be bonded. The bonding process also appears suspect, from what I’ve seen in various pictures of the frame & manufacturing process. Trek (OCLV) and others co-mold several 0.002” tall “pips” around the circumference and length of their “male” bonded tubes...those pips center the tube into the female lug (or tube) and ensure an optimal 0.002” thick bondline, and it ensures that the adhesive doesn’t get scraped out of place as the tube is inserted. I doubt Pivot did anything like those 2-thou pips, based on several of my observations. It’s also usually a good idea to “inject” a bit of structural epoxy bonding adhesive into a port at the bonded joint, after initial assembly with adhesive, to ensure the entire bondline is fully covered, saturated, and void-free. I don’t see that sort of adhesive-injection port feature on their frame (from my cursory review), but I think Specialized might do that on their prototype DH frames. I think Atherton does the same. It’s common in aerospace, F1, and even in the production of certain composite sports cars. I actually import special 3M structural adhesive from the UK (it’s what I used on McLaren’s carbon fiber “tubs” and Bentley Motors’ prototype carbon fiber doors for one of their Super Sports technology demonstrator cars) which is better than what’s available in the US (likely because it’s more toxic =) — it’s strong, and has superior mechanical & dynamic performance numbers, and is highly toughened (as well as being highly crosslinked for extra strength, if you post-cure it a bit around 250F to 350F after achieving initial bond strength at room temp, overnight. Engineers, prototype manufacturing technicians, and production manufacturing technicians, cannot mess around with bond failures — it has to be done right, and the materials and manufacturing processes have to enable bonding perfection. Every time. 

Also, Pivot appears to use cast-silicone custom bladders for their prototypes — and silicone / silicone oil can readily leach into the prepreg (unless significant protective countermeasures are taken). The silicone contamination can greatly adversely affecting bonding / adhesion. Aerospace companies ban everything silicone in their composites manufacturing facilities, for this reason. Even those yellow silicone “Livestrong” Lance Armstrong bracelets are strictly banned. Pivot’s custom composite tubes could have been contaminated with silicone that could affect their adhesive-bond performance — and their manufacturing pictures show the silicone bladder directly in contact with the uncured & cured carbon fiber prepreg, directly adjacent to the end of the tube (where the composite tube is subsequently bonded). Polyurethane, latex, molded nylon, or nylon film over polystyrene foam rigidized-bladder mandrels, are good alternatives for prototypes (and sometimes production).  

Lastly, the kink / bend in the carbon fiber downtube, just behind the lug, will put both sides of the downtube in compression right at the kink / downtube bend...and carbon fiber fails in compression. Although Kerr’s bike didn’t fail there, it’s a suboptimal compression-loading scenario which will result in pronounced compressive forces in the laminate on both the top and bottom sides of the downtube at the bend (in a jump-case loading scenario like Kerr experienced). Frames have to be engineered, in every way, for those worst-case cases...and engineering a frame with a tube geometrical configuration that results in substantial compressive forces on both sides of a composite tube is just questionable engineering, in my opinion. The goal should be to limit inducing those sort of compressive loads and mitigate the risk of composite compressive failure.

-WRCDH 

 

aka Pivot bikes, BIG TRASH 

dknapton wrote:

Writing multiple paragraphs over a couple blurry screen grabs and followong it up with Pivot is trash leads me to believe you might be a little...

Writing multiple paragraphs over a couple blurry screen grabs and followong it up with Pivot is trash leads me to believe you might be a little biased and can't be taken too seriously. 

gibbon wrote:

I just watched that and the race,.After qualifying first Bernard seemed way off the pace in his race run.I wonder if the de-bonding had already started...

I just watched that and the race,.After qualifying first Bernard seemed way off the pace in his race run.I wonder if the de-bonding had already started and he could feel something was off.
Looking at the specializeds I wondered if they had some additional mechanical fixing.

chamaedorea.elegans wrote:

Naw, it’s a fundamentally flawed design and manufacturing process (in terms of composites engineering), from what I can see from their prototype manufacturing pictures, as well...

Naw, it’s a fundamentally flawed design and manufacturing process (in terms of composites engineering), from what I can see from their prototype manufacturing pictures, as well as from Kerr’s broken frame pictures — in my opinion. Also, the fact that something is a prototype doesn’t mean that it’s permissible to utilize a dangerously designed / engineered / manufactured product, which could result in the substantial impairment or death of an athlete.  

The first flaw is the straight-insertion of the top tube AND the down tube into the lug, at the same draw angle. As such, if the bond isn’t perfect and the bondline fractures, the tubes are not mechanically constrained by different draw angles...both tubes pull out of the lug(s) in the exact same draw direction — that is a serious design / engineering flaw in my professional (composites engineering) opinion. If designed differently, with different draw angles for each tube / lug, both tubes likely would not experience the same stress vectors at the bondine (due to their varying orientation) and thus both bondlines likely wouldn’t fail at the same time. And both tubes would not (and could not) pull out of the lug(s) at the same time, in the same direction. With different draw angles / bondline orientation / stress vectors, one bondline would likely fail before the other, allowing detection of the bond failure. Likewise, the different draw angles (if the tube are stiff & strong enough) wouldn’t allow both tubes to pull out at the same time, in the same direction. Atherton got that right. Pivot got that wrong. It was a major oversight and a fundamental engineering flaw, in my opinion. That Pivot frame even has a separate individual top tube, and a separate individual down tube — so they didn’t need to utilize the same draw angle for both the top tube & down tube. (But the same draw angle would be required if the rest of front triangle was a single-piece composite molding and the top and down tubes weren’t separate pieces).  

Also, if the bondline wasn’t perfect, bonding failures can occur from bonding adhesive microcracking, adhesive macro-cracking, and incomplete adhesive coverage. Galvanic corrosion, and other corrosion, can be an issue with aluminum lugs and carbon fiber (unless the carbon fiber is insulated with fiberglass or similar non-conductive material). Aerospace companies often use fiberglass layers to prevent galvanic corrosion, making sure to not sand them off, nor sand too deeply into the fiberglass, where it bonds to aluminum. Likewise, at a minimum, they’ll typically hard anodize the aluminum, or use another bonding-optimized mil-spec surface preparation or treatment and/or anodizing process. Often, aerospace companies apply a military-spec type of cured epoxy primer onto the aluminum, to which the subsequent prepreg composite, or bonding adhesive, can tenaciously bond (and bond without corrosion due to the protective anti-corrosion epoxy coating). It appears Pivot excluded some or all of these critical (and fairly simple) steps. I also don’t see any fiberglass on the cured tubes, in the bonding area, in the prototype manufacturing pictures that Pivot released for publication on Pinkbike — it appears to be solely a woven carbon fiber surface layer, with no galvanic insulation layer, in the area bonded to the lug.

Additionally, it appears the bonding process was flawed — I didn’t seem to see much adhesive on the composite nor aluminum portions of the failed bond (in Kerr’s broken frame pictures). There’s a chance they didn’t properly remove mold release on the cured composite tubes. Or that they didn’t properly prepare the composite & aluminum surfaces (via abrasion and solvent cleaning), or that insufficient bonding adhesive was used, or that the adhesive scraped out of place during the assembly process...thus resulting in insufficient adhesive in the area to be bonded. The bonding process also appears suspect, from what I’ve seen in various pictures of the frame & manufacturing process. Trek (OCLV) and others co-mold several 0.002” tall “pips” around the circumference and length of their “male” bonded tubes...those pips center the tube into the female lug (or tube) and ensure an optimal 0.002” thick bondline, and it ensures that the adhesive doesn’t get scraped out of place as the tube is inserted. I doubt Pivot did anything like those 2-thou pips, based on several of my observations. It’s also usually a good idea to “inject” a bit of structural epoxy bonding adhesive into a port at the bonded joint, after initial assembly with adhesive, to ensure the entire bondline is fully covered, saturated, and void-free. I don’t see that sort of adhesive-injection port feature on their frame (from my cursory review), but I think Specialized might do that on their prototype DH frames. I think Atherton does the same. It’s common in aerospace, F1, and even in the production of certain composite sports cars. I actually import special 3M structural adhesive from the UK (it’s what I used on McLaren’s carbon fiber “tubs” and Bentley Motors’ prototype carbon fiber doors for one of their Super Sports technology demonstrator cars) which is better than what’s available in the US (likely because it’s more toxic =) — it’s strong, and has superior mechanical & dynamic performance numbers, and is highly toughened (as well as being highly crosslinked for extra strength, if you post-cure it a bit around 250F to 350F after achieving initial bond strength at room temp, overnight. Engineers, prototype manufacturing technicians, and production manufacturing technicians, cannot mess around with bond failures — it has to be done right, and the materials and manufacturing processes have to enable bonding perfection. Every time. 

Also, Pivot appears to use cast-silicone custom bladders for their prototypes — and silicone / silicone oil can readily leach into the prepreg (unless significant protective countermeasures are taken). The silicone contamination can greatly adversely affecting bonding / adhesion. Aerospace companies ban everything silicone in their composites manufacturing facilities, for this reason. Even those yellow silicone “Livestrong” Lance Armstrong bracelets are strictly banned. Pivot’s custom composite tubes could have been contaminated with silicone that could affect their adhesive-bond performance — and their manufacturing pictures show the silicone bladder directly in contact with the uncured & cured carbon fiber prepreg, directly adjacent to the end of the tube (where the composite tube is subsequently bonded). Polyurethane, latex, molded nylon, or nylon film over polystyrene foam rigidized-bladder mandrels, are good alternatives for prototypes (and sometimes production).  

Lastly, the kink / bend in the carbon fiber downtube, just behind the lug, will put both sides of the downtube in compression right at the kink / downtube bend...and carbon fiber fails in compression. Although Kerr’s bike didn’t fail there, it’s a suboptimal compression-loading scenario which will result in pronounced compressive forces in the laminate on both the top and bottom sides of the downtube at the bend (in a jump-case loading scenario like Kerr experienced). Frames have to be engineered, in every way, for those worst-case cases...and engineering a frame with a tube geometrical configuration that results in substantial compressive forces on both sides of a composite tube is just questionable engineering, in my opinion. The goal should be to limit inducing those sort of compressive loads and mitigate the risk of composite compressive failure.

-WRCDH 

 

aka Pivot bikes, BIG TRASH 

anotherbikerguy wrote:

Screenshot from Framework Bikes (no, not Neko's Frameworks; this is a road-focused company doing bonded alu/carbon frames) with yet another interesting theory about the failure mode...

Screenshot from Framework Bikes (no, not Neko's Frameworks; this is a road-focused company doing bonded alu/carbon frames) with yet another interesting theory about the failure mode of BK's bike:

(Disclaimer: I'm not an engineer. I don't know if this is correct.)

chamaedorea.elegans wrote:

Naw, it’s a fundamentally flawed design and manufacturing process (in terms of composites engineering), from what I can see from their prototype manufacturing pictures, as well...

Naw, it’s a fundamentally flawed design and manufacturing process (in terms of composites engineering), from what I can see from their prototype manufacturing pictures, as well as from Kerr’s broken frame pictures — in my opinion. Also, the fact that something is a prototype doesn’t mean that it’s permissible to utilize a dangerously designed / engineered / manufactured product, which could result in the substantial impairment or death of an athlete.  

The first flaw is the straight-insertion of the top tube AND the down tube into the lug, at the same draw angle. As such, if the bond isn’t perfect and the bondline fractures, the tubes are not mechanically constrained by different draw angles...both tubes pull out of the lug(s) in the exact same draw direction — that is a serious design / engineering flaw in my professional (composites engineering) opinion. If designed differently, with different draw angles for each tube / lug, both tubes likely would not experience the same stress vectors at the bondine (due to their varying orientation) and thus both bondlines likely wouldn’t fail at the same time. And both tubes would not (and could not) pull out of the lug(s) at the same time, in the same direction. With different draw angles / bondline orientation / stress vectors, one bondline would likely fail before the other, allowing detection of the bond failure. Likewise, the different draw angles (if the tube are stiff & strong enough) wouldn’t allow both tubes to pull out at the same time, in the same direction. Atherton got that right. Pivot got that wrong. It was a major oversight and a fundamental engineering flaw, in my opinion. That Pivot frame even has a separate individual top tube, and a separate individual down tube — so they didn’t need to utilize the same draw angle for both the top tube & down tube. (But the same draw angle would be required if the rest of front triangle was a single-piece composite molding and the top and down tubes weren’t separate pieces).  

Also, if the bondline wasn’t perfect, bonding failures can occur from bonding adhesive microcracking, adhesive macro-cracking, and incomplete adhesive coverage. Galvanic corrosion, and other corrosion, can be an issue with aluminum lugs and carbon fiber (unless the carbon fiber is insulated with fiberglass or similar non-conductive material). Aerospace companies often use fiberglass layers to prevent galvanic corrosion, making sure to not sand them off, nor sand too deeply into the fiberglass, where it bonds to aluminum. Likewise, at a minimum, they’ll typically hard anodize the aluminum, or use another bonding-optimized mil-spec surface preparation or treatment and/or anodizing process. Often, aerospace companies apply a military-spec type of cured epoxy primer onto the aluminum, to which the subsequent prepreg composite, or bonding adhesive, can tenaciously bond (and bond without corrosion due to the protective anti-corrosion epoxy coating). It appears Pivot excluded some or all of these critical (and fairly simple) steps. I also don’t see any fiberglass on the cured tubes, in the bonding area, in the prototype manufacturing pictures that Pivot released for publication on Pinkbike — it appears to be solely a woven carbon fiber surface layer, with no galvanic insulation layer, in the area bonded to the lug.

Additionally, it appears the bonding process was flawed — I didn’t seem to see much adhesive on the composite nor aluminum portions of the failed bond (in Kerr’s broken frame pictures). There’s a chance they didn’t properly remove mold release on the cured composite tubes. Or that they didn’t properly prepare the composite & aluminum surfaces (via abrasion and solvent cleaning), or that insufficient bonding adhesive was used, or that the adhesive scraped out of place during the assembly process...thus resulting in insufficient adhesive in the area to be bonded. The bonding process also appears suspect, from what I’ve seen in various pictures of the frame & manufacturing process. Trek (OCLV) and others co-mold several 0.002” tall “pips” around the circumference and length of their “male” bonded tubes...those pips center the tube into the female lug (or tube) and ensure an optimal 0.002” thick bondline, and it ensures that the adhesive doesn’t get scraped out of place as the tube is inserted. I doubt Pivot did anything like those 2-thou pips, based on several of my observations. It’s also usually a good idea to “inject” a bit of structural epoxy bonding adhesive into a port at the bonded joint, after initial assembly with adhesive, to ensure the entire bondline is fully covered, saturated, and void-free. I don’t see that sort of adhesive-injection port feature on their frame (from my cursory review), but I think Specialized might do that on their prototype DH frames. I think Atherton does the same. It’s common in aerospace, F1, and even in the production of certain composite sports cars. I actually import special 3M structural adhesive from the UK (it’s what I used on McLaren’s carbon fiber “tubs” and Bentley Motors’ prototype carbon fiber doors for one of their Super Sports technology demonstrator cars) which is better than what’s available in the US (likely because it’s more toxic =) — it’s strong, and has superior mechanical & dynamic performance numbers, and is highly toughened (as well as being highly crosslinked for extra strength, if you post-cure it a bit around 250F to 350F after achieving initial bond strength at room temp, overnight. Engineers, prototype manufacturing technicians, and production manufacturing technicians, cannot mess around with bond failures — it has to be done right, and the materials and manufacturing processes have to enable bonding perfection. Every time. 

Also, Pivot appears to use cast-silicone custom bladders for their prototypes — and silicone / silicone oil can readily leach into the prepreg (unless significant protective countermeasures are taken). The silicone contamination can greatly adversely affecting bonding / adhesion. Aerospace companies ban everything silicone in their composites manufacturing facilities, for this reason. Even those yellow silicone “Livestrong” Lance Armstrong bracelets are strictly banned. Pivot’s custom composite tubes could have been contaminated with silicone that could affect their adhesive-bond performance — and their manufacturing pictures show the silicone bladder directly in contact with the uncured & cured carbon fiber prepreg, directly adjacent to the end of the tube (where the composite tube is subsequently bonded). Polyurethane, latex, molded nylon, or nylon film over polystyrene foam rigidized-bladder mandrels, are good alternatives for prototypes (and sometimes production).  

Lastly, the kink / bend in the carbon fiber downtube, just behind the lug, will put both sides of the downtube in compression right at the kink / downtube bend...and carbon fiber fails in compression. Although Kerr’s bike didn’t fail there, it’s a suboptimal compression-loading scenario which will result in pronounced compressive forces in the laminate on both the top and bottom sides of the downtube at the bend (in a jump-case loading scenario like Kerr experienced). Frames have to be engineered, in every way, for those worst-case cases...and engineering a frame with a tube geometrical configuration that results in substantial compressive forces on both sides of a composite tube is just questionable engineering, in my opinion. The goal should be to limit inducing those sort of compressive loads and mitigate the risk of composite compressive failure.

-WRCDH 

 

aka Pivot bikes, BIG TRASH 

TheSuspensionLabNZ wrote:

Actually I'm staying out of this on second thoughts

TheSuspensionLabNZ wrote:

Actually I'm staying out of this on second thoughts

chamaedorea.elegans wrote:

Naw, it’s a fundamentally flawed design and manufacturing process (in terms of composites engineering), from what I can see from their prototype manufacturing pictures, as well...

Naw, it’s a fundamentally flawed design and manufacturing process (in terms of composites engineering), from what I can see from their prototype manufacturing pictures, as well as from Kerr’s broken frame pictures — in my opinion. Also, the fact that something is a prototype doesn’t mean that it’s permissible to utilize a dangerously designed / engineered / manufactured product, which could result in the substantial impairment or death of an athlete.  

The first flaw is the straight-insertion of the top tube AND the down tube into the lug, at the same draw angle. As such, if the bond isn’t perfect and the bondline fractures, the tubes are not mechanically constrained by different draw angles...both tubes pull out of the lug(s) in the exact same draw direction — that is a serious design / engineering flaw in my professional (composites engineering) opinion. If designed differently, with different draw angles for each tube / lug, both tubes likely would not experience the same stress vectors at the bondine (due to their varying orientation) and thus both bondlines likely wouldn’t fail at the same time. And both tubes would not (and could not) pull out of the lug(s) at the same time, in the same direction. With different draw angles / bondline orientation / stress vectors, one bondline would likely fail before the other, allowing detection of the bond failure. Likewise, the different draw angles (if the tube are stiff & strong enough) wouldn’t allow both tubes to pull out at the same time, in the same direction. Atherton got that right. Pivot got that wrong. It was a major oversight and a fundamental engineering flaw, in my opinion. That Pivot frame even has a separate individual top tube, and a separate individual down tube — so they didn’t need to utilize the same draw angle for both the top tube & down tube. (But the same draw angle would be required if the rest of front triangle was a single-piece composite molding and the top and down tubes weren’t separate pieces).  

Also, if the bondline wasn’t perfect, bonding failures can occur from bonding adhesive microcracking, adhesive macro-cracking, and incomplete adhesive coverage. Galvanic corrosion, and other corrosion, can be an issue with aluminum lugs and carbon fiber (unless the carbon fiber is insulated with fiberglass or similar non-conductive material). Aerospace companies often use fiberglass layers to prevent galvanic corrosion, making sure to not sand them off, nor sand too deeply into the fiberglass, where it bonds to aluminum. Likewise, at a minimum, they’ll typically hard anodize the aluminum, or use another bonding-optimized mil-spec surface preparation or treatment and/or anodizing process. Often, aerospace companies apply a military-spec type of cured epoxy primer onto the aluminum, to which the subsequent prepreg composite, or bonding adhesive, can tenaciously bond (and bond without corrosion due to the protective anti-corrosion epoxy coating). It appears Pivot excluded some or all of these critical (and fairly simple) steps. I also don’t see any fiberglass on the cured tubes, in the bonding area, in the prototype manufacturing pictures that Pivot released for publication on Pinkbike — it appears to be solely a woven carbon fiber surface layer, with no galvanic insulation layer, in the area bonded to the lug.

Additionally, it appears the bonding process was flawed — I didn’t seem to see much adhesive on the composite nor aluminum portions of the failed bond (in Kerr’s broken frame pictures). There’s a chance they didn’t properly remove mold release on the cured composite tubes. Or that they didn’t properly prepare the composite & aluminum surfaces (via abrasion and solvent cleaning), or that insufficient bonding adhesive was used, or that the adhesive scraped out of place during the assembly process...thus resulting in insufficient adhesive in the area to be bonded. The bonding process also appears suspect, from what I’ve seen in various pictures of the frame & manufacturing process. Trek (OCLV) and others co-mold several 0.002” tall “pips” around the circumference and length of their “male” bonded tubes...those pips center the tube into the female lug (or tube) and ensure an optimal 0.002” thick bondline, and it ensures that the adhesive doesn’t get scraped out of place as the tube is inserted. I doubt Pivot did anything like those 2-thou pips, based on several of my observations. It’s also usually a good idea to “inject” a bit of structural epoxy bonding adhesive into a port at the bonded joint, after initial assembly with adhesive, to ensure the entire bondline is fully covered, saturated, and void-free. I don’t see that sort of adhesive-injection port feature on their frame (from my cursory review), but I think Specialized might do that on their prototype DH frames. I think Atherton does the same. It’s common in aerospace, F1, and even in the production of certain composite sports cars. I actually import special 3M structural adhesive from the UK (it’s what I used on McLaren’s carbon fiber “tubs” and Bentley Motors’ prototype carbon fiber doors for one of their Super Sports technology demonstrator cars) which is better than what’s available in the US (likely because it’s more toxic =) — it’s strong, and has superior mechanical & dynamic performance numbers, and is highly toughened (as well as being highly crosslinked for extra strength, if you post-cure it a bit around 250F to 350F after achieving initial bond strength at room temp, overnight. Engineers, prototype manufacturing technicians, and production manufacturing technicians, cannot mess around with bond failures — it has to be done right, and the materials and manufacturing processes have to enable bonding perfection. Every time. 

Also, Pivot appears to use cast-silicone custom bladders for their prototypes — and silicone / silicone oil can readily leach into the prepreg (unless significant protective countermeasures are taken). The silicone contamination can greatly adversely affecting bonding / adhesion. Aerospace companies ban everything silicone in their composites manufacturing facilities, for this reason. Even those yellow silicone “Livestrong” Lance Armstrong bracelets are strictly banned. Pivot’s custom composite tubes could have been contaminated with silicone that could affect their adhesive-bond performance — and their manufacturing pictures show the silicone bladder directly in contact with the uncured & cured carbon fiber prepreg, directly adjacent to the end of the tube (where the composite tube is subsequently bonded). Polyurethane, latex, molded nylon, or nylon film over polystyrene foam rigidized-bladder mandrels, are good alternatives for prototypes (and sometimes production).  

Lastly, the kink / bend in the carbon fiber downtube, just behind the lug, will put both sides of the downtube in compression right at the kink / downtube bend...and carbon fiber fails in compression. Although Kerr’s bike didn’t fail there, it’s a suboptimal compression-loading scenario which will result in pronounced compressive forces in the laminate on both the top and bottom sides of the downtube at the bend (in a jump-case loading scenario like Kerr experienced). Frames have to be engineered, in every way, for those worst-case cases...and engineering a frame with a tube geometrical configuration that results in substantial compressive forces on both sides of a composite tube is just questionable engineering, in my opinion. The goal should be to limit inducing those sort of compressive loads and mitigate the risk of composite compressive failure.

-WRCDH 

 

aka Pivot bikes, BIG TRASH 

colby wrote:

Chamaedorea is the biggest MORON 

dknapton wrote:

Writing multiple paragraphs over a couple blurry screen grabs and followong it up with Pivot is trash leads me to believe you might be a little...

Writing multiple paragraphs over a couple blurry screen grabs and followong it up with Pivot is trash leads me to believe you might be a little biased and can't be taken too seriously. 

colby wrote:

It’s a Proto version !  there could have been a error in the gluing preparation cleaning process  end of story! Bike’s brake all the time!  the...

It’s a Proto version ! 

there could have been a error in the gluing preparation cleaning process 

end of story! Bike’s brake all the time! 

the production version will be some of the best there is like all pivot bikes ! 
and yes prototyping is a part of racing development! 
chill out 

LePigPen wrote:

Chris just admitted on pinkbike that their treatment of the aluminum didn't work properly to avoid corrosion which caused the epoxy to not bond correctly. So...

Chris just admitted on pinkbike that their treatment of the aluminum didn't work properly to avoid corrosion which caused the epoxy to not bond correctly. So yes. There was an error. Pivot's production bikes are good. But that gluing error could have fcuked BK up properly. No point in just dismissing it as innovation. That was a big fcuk up on Pivot's part, but props to them for admitting it and hopefully they clean up that process. They've already recalled the frames that would have been made the same way (sadly, presumably the fresh new bikes Ed and Jenna got)... And are going to test them to failure most likely.

Innovation is great. Ideally it shouldn't be at the cost of an athlete. Can't wait to see all the Pivot team members ride this year. Jakob and Dane are great.