Trailer Wheel Failure

J.E.I. Metallurgical, Inc., Dallas, Texas, was asked to conduct a field visual and microscopic examination of the trailer wheel failure.

The trailer, as originally viewed, is shown in Photographs 1 (B004), 2 (B002) and 3 (B008).

Photograph 1  Overall left side view of subject trailer.

Photograph 2  Left rear quarter view of subject trailer.

Photograph 3  Right front quarter view of subject trailer. Arrow denotes area of right front axle failure.

The right front axle was observed to have fractured (see arrow in Photograph 3) and displayed a fully circumferential weld fracture.

A close-up view of the trailer side of the axle fracture is shown in Photograph 4 (E002).  This photograph was taken by parties unknown at or near the time of the subject accident.

Photograph 4  Overall view of trailer side of subject axle fracture.  Areas of interest are noted.

The view presented in Photograph 4 was photographed at the accident scene (or shortly thereafter) and clearly shows the trailer side of the axle fracture.  The fresh weld fracture surface shown in Photograph 4 has several distinct areas.  The area denoted #1 is a grainy fracture typical of final fracture zone overload.  The area denoted #2 presents a smooth, velvety, gray stepped or progressive stepwise fracture.  A crack in the trailer side of the axle weld is denoted by #3.  The area denoted #4 presents a dark, shallow thumbnail in the area of final separation.  The area denoted #5 appears to be a progressive stepwise smooth gray fracture similar (but with some discrete differences) to the area denoted in #2.

The axle side of the fracture, with attached wheel, is shown in Photograph 5 (E001). Photograph was taken by parties unknown at, or near the time of the subject accident. The axle and axle fracture are relatively free from corrosion.

Photograph 5  Perspective view of the axle failure near the final fracture zone. Dark thumbnail fracture is denoted with white arrow.

The dark thumbnail fracture is clearly denoted with a white arrow in Photograph 5.

Visual examination of the failed wheel side of the fractured axle and fracture surface revealed that they were highly corroded.  The examination also revealed that the axle-to-brake backing plate flange was bowed or deformed.  The deformed axle flange plate is shown in Photograph 6 (B051).  The deformed area of the axle-to-brake backing plate is denoted with arrows.

Photograph 6  Perspective view of failed axle.  Deformation of axle-to-brake backing plate is denoted with arrows.

A close-up view of gouging deformation in the final fracture area is shown in Photograph 7 (D009).  The areas of final fracture and of gouging deformation are denoted in Photograph 7.

Photograph 7  Overall view of failed axle. Gouging deformation is denoted with arrows.

Shown in Photograph 8 (B050), is a perspective view showing the axle surface deformation (rub) and the final fracture area.

Photograph 8  Perspective view of failed axle near the area of final fracture area. Rub or wearing of the machining marks on the machined axle surface is noted.

Shown in Photograph 9 (D021), is a close-up view of an area of rub, where circumferential machining tool marks on the surface of the axle have been worn or rubbed away from contact with the surrounding collar prior to complete axle separation.

Photograph 9  Area on machined surface of the subject axle where machining tool marks have been obliterated and worn away as a result of rubbing against the surface within which the axle rotates.

Shown in Photograph 10 (C043) are two areas of interest at approximately 90° and 180° from final fracture (possible fracture origin areas). 

Photograph 10  Possible fracture origin areas are noted.  Rubbing on the outside axle surface created damage and a “fold over lip” at the fracture edge.

A perspective view near the final fracture area is shown in Photograph 11 (D015).   For position location note red (dye) area or ink on fracture surface about 90° counter clockwise from final fracture area.

Photograph 11  Perspective view of final fracture area.

A close-up view of the weld fracture near the final fracture zone is shown in Photograph 12 (D026).

Photograph 12  Rub area about 90° counter clockwise from final fracture area.

Wear and lipping over of the axle surface, at and over the fracture edge, is denoted with arrows in Photograph 12.

A close-up view of the edge wear/lipping is shown in Photograph 13 (D027).  The edge wear/lipping indicates that the fracture at this location had been present for a sufficient time for rubbing and wear to have occurred on the axle surface and to have “lipped over” the edge of the fracture.

Photograph 13  Close-up view of edge wear and lipping in area of arrow and red marker.

The right front trailer wheel to which the failed outer axle was attached is shown in Photograph 14 (B174).  The right rear (RR) wheel is shown for comparison purposes.

Photograph 14  Overall view of right front (RF) and right rear (RR) trailer wheels/rims.

The right front trailer wheel is denoted (RF) in Photograph 14.  The right rear wheel is denoted (RR).  Of particular note is the fact that both wheel rims are deformed in an identical manner.

The right rear (RR) axle spindle and failed wheel bearing are shown in Photograph 15 (B208).  Distinct downward bending, bowing and permanent deformations of the spindle are evident.

Photograph 15  Overall view of right rear (RR) spindle.  Downward permanent deformation is clearly evident.

Significant plastic deformation and bending of the axle mounting flange is also evident and denoted with a white arrow.

The deformed right front (RF) spindle is shown after removal from the right front wheel rim in Photograph 16 (B202).

Photograph 16  Deformation of right front trailer axle spindle.  Deformation which is more pronounced at the end of the spindle is clearly evident.

The deformed right front trailer spindle and axle failure are shown in Photograph 17 (B204).

Photograph 17  Profile view of axle failure and spindle deformation after removal from right front trailer wheel.

What appears visually to be the axle final fracture area, is denoted with an arrow in Photograph 17.

It was also noted that the left front trailer wheel was canted (tilted) and pushed out with respect to the left rear wheel.  A perspective view of the left trailer wheel is shown in Photograph 18 (B206).

Photograph 18  Overall view of left front trailer tire.  Black arrow denotes outward movement of the front and tire contact surface.  The white arrow denotes inward movement of the “rear” and upper part of the front trailer tire.

The front and bottom of the left front wheel/tire appears to be pushed outward (see black arrow) and the back of the front tire (nearest the left rear tire) appears to be “pushed inward” (see white arrow).  Arrows in Photograph 18 show the area of displacement.

Also noted on the left wheel rim was a label.  A close-up view of the label is shown in Photograph 19 (B135).

Photograph 19  Close-up view of warning label on left side trailer wheel rim.

It is noted that the label indicates a wheel rim load capacity of 3,750 pounds.

An overall view of the trailer hitch is shown in Photograph 20 (B123).

Photograph 20  Overall view of subject trailer hitch.

It was visually apparent that two I.D. specification labels, one placed over the other, were present on the trailer tongue.

A close-up view of the trailer hitch specification tag is shown in Photograph 21 (B124).

Photograph 21  Close-up view of subject trailer hitch.  Note gross trailer weight is designated as 7000 pounds for this trailer coupling.

It is noted, per the specification tag, that the gross trailer weight is designated to be 7,000 pounds for this trailer hitch.

A slightly rotated view of the trailer hitch I.D. label is shown in Photograph 22 (B127).

Photograph 22  Tags (two) visible on subject trailer hitch.

The reference, “1,050#” noted in Photograph 22 is unknown, but could be related to the “ball load”.

The trailer ball socket hitch exhibited the designation GVWR 7,000 lb. as indicated in Photograph 23 (B129).

Photograph 23  Trailer ball socket hitch with 7000 pound GVWR indicated.

A view of the axle I.D. tag is shown in Photograph 24 (B142).

Photograph 24  Axle I.D. tag indicating that each trailer axle has a 7,000 pound capacity.

An axle capacity of 7,000 pounds is noted on the I.D. tag.  This weight capacity is designated for each of the two trailer axles.

This trailer axle failure presents several interesting features:

· The four (4) different fracture surface textures as shown in Photograph 4 support the proposition that the subject wheel did not detach from the subject trailer as a result of the rollover, i.e., single impact loading.

· The wear on the machined axle surface suggests that the axle was “loose” and/or cracked and over time was able to move, rub on and abrade the circumferential tool marks on the machined axle surface. 

· The above facts and evidence argue strongly for an axle weld failure that was time dependent.  That is, the weld fracture surface increased and grew in size over time (and usage), i.e., the axle weld failure did not occur as a result of an instantaneous force brought about by the rollover accident.

· The edge of the axle fracture surface was “lipped over” the fracture as shown in Photographs 10 and 12.  This supports the theory of progressive stepwise cracking of the weld prior to the trailer rollover. 

· The axle-to-brake backing plate flange on the subject axle exhibited a small amount of bowing or permanent deformation, as shown in Photograph 6.

· The massive deformation displayed by the right rear (RR) axle-to-brake flange, displayed in Photograph 15, confirms that very large forces were experienced in the rollover causing the right rear (RR) wheel failure.

From the above, it is evident that failure of the axle weld has been progressive and the weld cracking occurred as the trailer was being used prior to the trailer rollover.  The outer axle side weld fracture was heavily rusted and laboratory cleaning and laboratory destructive testing of the weld was needed to ascertain the extent and type of welding defect present.  That is, the rapid failure of the weld (less than three months trailer usage) suggests a welding defect and/or improper choice of weld filler metal strength (under-strength weld).  The variation in weld fracture surface appearance and the existence (visual determination) of cracking in the weld also suggest defective welding and/or under-strength weld bead. However, the presence of a welding flaw (not of sufficient size to be classified as a defect) does not necessarily condemn the flawed weld to be the root cause of the subject accident.

Additionally, visual evidence suggests that trailer overload and/or improper design/load distribution may have caused and/or aided and abetted the fracture process.  The evidence for overloading of the trailer components are:

· The right rear (RR) axle spindle, shown in Photograph 15, is highly deformed.  This deformation suggests an axle overload condition. However, this deformation and overload forces probably occurred as a result of loads and forces experienced by the wheel and axle during the rollover accident.

· Deformation of the right front (RF) axle spindle in all probability occurred prior to the axle weld failure.  The massive amount of force necessary to cause that amount of plastic/permanent deformation is not likely to have resulted from post weld failure impact to the right front trailer wheel.

· The deformation of the right front (RF) wheel rim suggests that an overload of the axle and wheel rim caused the observed wheel rim deformation prior to the axle weld failure and axle separation.

· The right rear (RR) wheel rim is observed to be deformed identically to the right front wheel rim.  Failure of the right front (RF) axle weld, pre-rollover, would have transferred significant trailer load to the right rear axle and right rear (RR) wheel rim thereby exceeding the wheel rim load limit and thus overloading the right rear (RR) wheel rim.  The deformation of the right front (RF) and rear wheel rims appears quite similar. 

· The canted/tilted condition of the front left trailer axle wheel, without visible deformation of the left trailer fender and/or nearby structure suggests that the canted condition may have resulted from a trailer/axle overload condition.  This would contribute to the observed pre-rollover weaving of the trailer on the highway.

· The severely deformed right rear axle-to-brake backing plate flange, as shown in Photograph 15, suggests that this deformation probably resulted during the trailer rollover.

· The very slight deformation of the right front (RF) axle-to-brake backing plate flange suggests that this small, but significant, deformation was the result of trailer overload prior to the axle weld failure.  

It was reported that the equipment mounted on the trailer weighed (assume dry weight) in the order of 9,000 plus pounds. 

· The trailer hitch, as shown in Photograph 23, is specified as a “GVWR 7,000 lb” trailer hitch.

· The trailer axles are each rated, as shown in Photograph 24, as being 7,000 pound axles.

The weight distribution of the trailer between trailer tongue and the front and rear axles is unknown.  However, it appears as if the subject trailer, as equipped, was overloaded.  That overload had been manifest by deformation (bending) in the various subject trailer axle and wheel components.

Opinions and Conclusions

Based on the investigation that has been conducted to date, several conclusions and opinions can be stated.  These opinions and conclusions are based on my education, professional training and over forty-three years of experience conducting metallurgical failure analysis and accident investigation.  These conclusions and opinions are stated and believed to be true to a reasonable degree of engineering certainty.  The opinions I hold at this time are:

1. The axle weld on the subject trailer may have been defectively manufactured.

2. The design specifications and engineering drawings were not available to this investigator.  Design specifications, i.e., engineering drawings and welding rod/wire specifications must be reviewed and examined in order to evaluate the adequacy of weld strength.

3. Cleaning of the weld fracture surface and metallurgical testing must be performed to evaluate the possibility of defective welding when the trailer was manufactured.

4. Deformation of key components in the trailer axle/wheel rims, axle components and wheels, etc. provide strong evidence of an overload failure process/mechanism, i.e., the load which was mounted on the trailer overloaded the trailer as it had been designed and configured.

5. The trailer hitch gross vehicle weight rating of 7,000 pounds appears to have been exceeded by the gross vehicle weight of the trailer and mounted equipment.

6. The trailer may have been inadequately designed to haul and carry the weight of the equipment mounted on the subject trailer.

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