Failure statistics of carbon fiber vs aluminum mountain bikes? I've read a lot of carbon fiber vs aluminum debates. The anecdotal evidence for one being better than another is not very interesting to me. I'm interested in the statistics.

Does anyone know where I can find actual failure stats for mountain bike frames? How many warranty repairs per year for each type vs sales volume, for example? Anyone work at a bike shop that can share the average number of people coming in per week with broken aluminum vs carbon fiber frames?
I've read a lot of carbon fiber vs aluminum debates.
  Does anyone know where I can find actual failure stats for mountain bike frames? How many warranty repairs per year for each type vs sales volume, for example?


I'm reading this as a strength of materials focused question - carbon vs aluminum.  

Summary:
For a properly designed, well made frame on a correctly assembled bicycle ridden in a manner that is not abusive (I know "abusive" is a relative term. A good frame should be over engineered to handle some abuse, say 80% - so I'm talking about the 20%) frame failure for carbon or aluminum is a non-factor.

However, warranty frame repairs/replacements data would be made up of:
- Material failures (that your question refers to)
- Manufacturing failures
- Flat out user abuse (the 20%)
- Incorrect assembly
- Damage during shipping
This statistic would not provide an accurate reflection of the merits of the two materials.

Generating reliable, comparable, standardized statistical data is expensive and tricky. There is no motivation for the bicycle industry to spend the money to generate this information or to share the data they have for many reasons. Frame design / styles change so frequently that even if the data were generated it would be outdated quickly. 

We don't have reliable, comparable, standardized statistical data that allow us to compare specific frames or types of frames to each other we do strength of materials data that we can use as an indicator of the merits of the two materials.

Manufacturing Technology for Aerospace Structural Materials
Fig 7.2
  


  Composites do not corrode and their fatigue resistance is outstanding. Corrosion of aluminum alloys is a major cost, and a constant maintenance problem, for both commercial and military aircraft. The corrosion resistance of composites can result in major savings in supportability costs. The superior fatigue resistance of composites, compared to high strength metals, is shown in Fig. 7.2. As long as reasonable design strain levels are used, fatigue of carbon fiber composites should not be a problem





  The specific strength (strength/density) and specific modulus (modulus/density) of high strength fiber composites, especially carbon, are higher than other comparable aerospace metallic alloys.


From a strength of material perspective carbon is more fatigue resistant and higher strength than aluminum.
The materials are more than adequate to the task.
What matters is:
- Frame design
- Correct frame construction
- Correct assembly of the bicycle  

In an ideal world (one without people who would cut corners making bike frames) you should be able to base your decision on the riding qualities of the two materials and your personal preferences.

So, select a trust worthy brand/frame maker and make sure your bike is assembled by a knowledgeable person and base your buying decision on your personal riding preferences.