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Truck Hood Wire Cable Failure

The failure of hood over wire rope safety cables was asserted to have caused a 500-pound truck tractor hood to fall during an engine compartment inspection and onto a truck driver causing physical injury.

An exemplar tractor with hood rotated into the open hood position is shown in Photograph A

Overall view of truck
Photograph A.  An overall view of similar, exemplar, truck tractor with the hood rotated to an open posiiton.

A close-up view is shown in Photograph B. The subject safety cable is denoted with an arrow in Photograph B.

Close-up view of
Photograph B.  A view of an open hood denoting the subject safety cable with an arrow.

A close-up view of the safety cable denoted with an arrow, and spring is shown in Photograph C.

Close-up View of the
Photograph C.  A close-up view of the safety cable and extension spring.

The safety cable and spring are present on both sides of the tractor.  An arrow in Photograph C denotes the left wire cable. The hood retention springs from the subject vehicle could not be produced for examination and evaluation.

A typical section of the 3/32-inch diameter (0.094 inches) wire cable is shown in Photograph D. The other end section of the cable is shown in Photograph E.

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Close-up view of attachment eyelet and failed wire cable.
Photograph D.   A close-up view of the attachment eyelet and failed wire cable.
Overall view of longer section of
Photograph E.  A view of the longer section of  the cable.

A close-up view of the failed end of the cable shown in Photograph E is depicted in Photograph G. A close-up view of the cable failure is shown in Photograph F.

Close-up view of failed strands in cable
Photograph F.  A view of the failed strands in the wire cable.

The Keyence Digital Microscope (KDM) was used to examine and record the individual wire end failures. A close-up view of two of the individual wire failures in failed wire ends on the eyelet are shown in Photograph G.

A close-up view of two of the individual wire failures in Photograph G revealed typical Cup and Cone tensile type fracture appearance.

Close-up view of overloaded wires
Photograph G.  A close-up view of the overloaded wires exhibiting cup and cone fractures.

Overload, cup and cone failure has a distinctive appearance on wires, rods and standard round tensile specimens and is an indication of a tensile overload failure. A cup and cone fracture appearance would be created if the cable had failed due to a strong wind or being dropped (without the retainer springs in place) so as to apply on impact, load to the subject wire strands. Of particular note is the visual presence of dirt within the cup and cone fracture. This dirt debris indicates that the subject-overloaded wires were in the failed condition for an extended time.

 Another view of wires from the failed wire strand is shown in Photograph H.

Failed wires from the failed hood safety cable showing extreme wear (chiseled) on several strand wires.
Photograph H.  Failed wires from the failed hood.

The chisel type failure shown in Photograph H is indicative of long-term wear of the individual wire strands either before or after the subject accident. Similar individual wire wear is shown in Photograph I.

Extreme wire wear on wires in broken strand.
Photograph I.  Extreme wire wear on wires in the broken strand.

Photograph J shows two failed wires exhibiting cup and cone fracture.

Two failed wires with cup and cone fracture appearance.
Photograph J.  Two failed wires with cup and cone fracture appearance.

However, it should be noted in Photograph J that the wires are also abraded along one side. This rub and reduction in wire diameter is believed to have occurred to the subject wires after the wires had failed.

Two additional wire failures from cable A are shown in Photograph K.

Close-up view of two failed wires from cable A.
Photograph K.  A view of two failed wires from cable A.

The remarkable appearance of the two cable wires in Photograph G is the fact that the longer failed wire presents a cup and cone failure, which has a portion of the cup side of the fracture worn flat into the cup topography.  The subject wire failed from overload and then that failed wire was worn by rubbing against other wires and/or vehicle components for an extended time period.

The shorter failed wire presents a chiseled, abraded cross-section indicating abrasion occurred simultaneously on two sides of the subject wire and/or occurred sequentially on each side of the subject wire. The flat fracture between the chiseled wire surfaces could be indicative of a fatigue fracture. 

The wire strand failure shown in Photograph L presents completely worn wires.  These wires with cup and cone fracture and with wear on one side of the wires and what appears to be cup and cone fractured wires all at one failure location.

 KDM of wire strand failure shows wires completely worn in two pieces and cup and cone failures with subsequent wear.
Photograph L.  Keyence Digital Microscope (KDM) photograph of the wire strand failure shows wires completely worn through.

A wire from the failed B wire cable is shown in Photograph M.

Failure wire exhibiting wire abrasion following the formation of cup and cone fracture
Photograph M.  Failed wire exhibiting wire abrasion.

The wire depicted in Photograph M shows a cup and cone fracture indicating overload.  But subsequent wire wear, to the extent of wearing down the side of the wire, was worn away.

Photograph N shows wear in two of the four wires in the cable, which had been overloaded (cup and cone fracture) but then by subsequent usage, was significantly worn away.

Close-up view of several wires exhibiting cup and cone overload fracture but subsequent wearing away of the already fractured wires.
Photograph N.  A view of several wires exhibiting cup and cone overload fracture.

It was claimed that after the incident, the vehicle was driven  approximately twenty miles to a repair facility with the subject failed hood cables still in place under the hood of the subject vehicle.

Evidence of cup and cone fracture where the cup and cone fracture features were filled with dirt and debris, strongly suggested that both of the hood safety cables had failed a significant time prior to the subject accident. In like manner, the failure and major abrasive wear of multiple safety cable wires must have required more than twenty miles to create the side of the wire wear and abrasion pattern observed during the Keyence Digital Microscope examination.

Based on the evidence examined, it was concluded that failure of both of the safety cables probably preceded the alleged accident. The evidence proved the existence of heavy dirt and debris inside the cup side of the cup and cone fracture. Wear on the edge of wire had obviously failed over a significant time prior to the day of the accident.

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J.E.I. Metallurgical, Inc.

5514 Harbor Town
Dallas, Texas 75287

Phone: (972) 934-0493
Fax: (469) 737-3938
Email: r.c.jerner@metallurgist.com

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