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Questions tagged [failure-analysis]

36 questions
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How do I properly compute mean time to failure?

I have a product of which we have shipped something like 500 units over the last five years. This product is not intended to be user serviceable; a failure of any component results in the unit being replaced. The majority of these units have never…
Stephen Collings
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What ASTM standard would be appropriate for testing the breaking strength of nylon ropes

ASTM D4268-93 would appear to be the relevant testing standard, but this was withdrawn in 2002 and is no longer active. Is there a current standard?
user8908459
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How to apply static failure criteria for bending stress in an angled cylindrical surface?

Let’s say I have an irregularly shaped bearing with a cross section that looks like the angled surface of a conical frustum, shown below. If a bending moment is applied which causes the inside diameter to ‘cave outwards’, how would I perform a…
juggling_pro
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What type of failure is this?

The part is a clevis and was insterted in a steering rack . Part was in Tension, torsion and bending. It failed at the end of the threaded bolt part. Is it a common problem for bolted joints ? How can it be resolved ? At first a bend was observed in…
Anshuman Sinha
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In a pre stressed concrete? Why is the top fiber considered as under compressive stress?

I have been solving problems involving pre stress concrete, i want to clarify why is the top fiber always considered as under compressive force, in my understanding the concrete would bend positively to due pre stressing and thus top fiber would be…
Shear at its finest
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Is a motor failure caused by a defect bearing considered to be a failure mode or is it higher vibration and speed loss in FMEA/FMECA?

Let us assume we have a motor with a bearing which is exhibited to wear. Over time, we can observe higher vibration, increased noise and the motor speed reduces due to the bearing fault. In the end, the bearing fails and the motor is not able to…
user3352632
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DOE analysis or root cause analysis?

For any testing that a part is suppose to pass a test, let's say the leakage test of a seal flange. How should I individualize the cause? I know there is root cause analysis and for different cases I probably need Design of Experiment (DOE)…
FabioSpaghetti
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How to sample Mean-Time-To Failure values from a Weibull Distribution with shape 1.5?

I have a mean time to failure (MTTF) recorded from 100 systems which is 6.5 years. The shape parameter of my component is given with k = 1.3 (based on a list the from literature). Now I want to sample (generate) further failure times based on a…
user3352632
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What is the difference between tau = VQ/It and tau = V/A?

What is the difference between the formulas $\tau = VQ/It$ and $\tau = V/A$ for finding shear stress due to transverse loading? I understand that the use of first moment of area, is the only reason for the more complex formula to account for…
juggling_pro
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Failure due to shear stress on rod lip?

Let’s say I have a circular rod that has an outside lip with a larger diameter and certain height. The rod moves axially, and the intent of the lip is to mechanically stop the rod at a maximum axial displacement. How would I calculate the maximum…
juggling_pro
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What is the longevity of Delrin rollers on aluminum linear rail?

I am in the process of selecting a linear rail system for a 5ft x 10ft cnc laser cutter. Delrin polymer rollers on 2 inch square extruded aluminum tube is an economically attractive solution. I have had success with them on a 3d printer, but I am…
ericnutsch
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How can I describe cold work and atomic structure?

A copper wire (42 cm x 0.25 cm diameter) twisted to failure did not change its dimensions significantly. How can I visualize or quantify the cold work done (tensile at the exterior, compressive in the interior)? Does it still have a regular…
Jim Gaidis
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Determining If A Test Article Is Suitable For X RAY Following Shock Testing?

I am interested in putting a small (3"x3"x2") assembly under X-ray, following a shock test, in order to evaluate failures of an internal ceramic piece. Unfortunately, this assembly utilizes quite a bit of potting material (epoxy) and as such, cannot…
Austin Prater
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Factors favoring crack propagation in the middle of a plate for an extensive length relative to plate thickness (Reasons for < marks on crack surface)

I have a scenario where we have encountered a cracked steel plate where the crack has propagated within the plate longitudinally for an extensive length. The plate thickness is 1", and the crack length is approximately 12" with somewhat of a bend…
Isa
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How to calculate the failure rate of a machine with probability and mean failure time?

I dont know how to approach this problem. Suppose that a machine has a probability of failure of 43% at 90 hours of operation. How can you calculate the failure rate and the probability of surviving x hours without having failures?
Jesus Oropeza Maray
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