5 votes

How do I properly compute mean time to failure?

First off, always remember that garbage in = garbage out; so if your data is garbage then your statistics will be garbage. In this situation your optimal data would be something like Run Hours Until ...
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4 votes

How do I properly compute mean time to failure?

If you don't have hard data, making assumptions (preferably "reasonable" ones) is the only option you have. (Maybe that's why engineers used to call their slide rules "guessing sticks...") You can't ...
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  • 12.5k
4 votes

What does 1 x rpm or 2 x rpm or 3 x rpm in vibration analysis mean?

RPM = revolutions per minute. In the context of vibration monitoring, 1 x rpm means a vibration frequency that is the same as the rotation speed (one vibration oscillation per revolution of the ...
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  • 12.5k
3 votes

What is the difference between tau = VQ/It and tau = V/A?

As mentioned, the formula $\tau_{avg}=\frac{V}{A}$ is called average shear stress. In some calculations it might suffice to calculate $\tau_{avg}$ for a widely used cross-section (let's say a ...
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  • 1,146
3 votes
Accepted

Hardening and Brittleness

Brittleness describes the inability of a material to absorb a considerable amount of plastic deformation. Thus, the material fails without a lot of deformation. Hardening, on the other hand is the ...
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  • 1,146
2 votes
Accepted

What type of failure is this?

this is a classic fatigue fracture, caused by a cyclic/reversed bending load superimposed on a static tension load. The cyclic load is caused by the reversed bending; the neutral axis shows clearly as ...
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2 votes

How do I properly compute mean time to failure?

The statistical tool Weibull as suggested by the previous two responded is the tool of choice for Mean Time To Failure (MTTF) calculations. Based on your comment as capture below, it appears that ...
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2 votes

DOE analysis or root cause analysis?

Let assume a leak has been reported in the following pump system. As a result there is 1 inch of water on the floor. To identify the failure a root cause analysis (RCA) needs to be performed. To ...
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2 votes
Accepted

Determining If A Test Article Is Suitable For X RAY Following Shock Testing?

X-rays are a poor way to test for cracking in a ceramic. A crack in a ceramic part which has not shattered to pieces is a very small feature, of order ~0.001" wide or less, which commonly-used x-ray ...
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2 votes

What ASTM standard would be appropriate for testing the breaking strength of nylon ropes

Go directly to the ASTM site. I put "nylon rope" in search and it said there were 154 possibilities.
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  • 5,728
2 votes
Accepted

Incorporating a dichotomous failure model for sustainment analysis

Modeling future behavior using past behavior is fraught with pitfalls. This is why we test large numbers of parts before turning the factory on and stocking the product in the warehouse. That said... ...
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1 vote
Accepted

Are there disadvantages to using a single multispan beam, vs separate simple beams, for materials that tolerate tension as well as compression?

The stress-strain diagrams will be different, but not enought to drive the design. The bottom would have lower deflection because the beam must be constant through the center support. Compare two ...
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  • 4,408
1 vote

Why does the max principle stress at yielding for a ductile material equal to its yield strength in a uniaxial tensile test?

Actually it is. When a material is loaded the stress state in the material is the same - it does not depend on the orientation that the stresses are analysed. Mohr's circle is a way of visualising a ...
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  • 22.6k
1 vote

What ASTM standard would be appropriate for testing the breaking strength of nylon ropes

Probably ASTM A931 - 18 Standard Test Method for Tension Testing of Wire Ropes and Strand There are others closely related but not exactly the same. ASTM F3410 - 19 Standard Test Method for ...
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1 vote
Accepted

DOE analysis or root cause analysis?

I think you might be mixing up the intentions of the two analysis tools you you mentioned - Root Cause Analysis and Design of Experiments. Consider thinking of it this way: Root Cause Analysis is ...
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  • 106
1 vote

Factors favoring crack propagation in the middle of a plate for an extensive length relative to plate thickness (Reasons for < marks on crack surface)

At the time of 1994 Northridge earthquake in California, I along with many other engineers inspected several four and five story damaged buildings to assess the urgent safety situation. We observed ...
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  • 20.9k
1 vote

Ductile,Brittle and Malleable

Ductile ("able to be drawn out into a thin wire") makes sense as the failure method, because the test is stretching the sample. Malleable ("able to be hammered or pressed into shape without breaking ...
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1 vote

How to apply static failure criteria for bending stress in an angled cylindrical surface?

This is a typical case of stresses on shells and plates and obviously lends itself to analyzing using polar coordinates. If your element is a thin shell and is loaded in a way that only membrane ...
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  • 20.9k
1 vote

Failure due to shear stress on rod lip?

This is very similar to the punching shear in column caps. One would calculate the shear at a distance d/2 away from the rod, with d being the thickness of flange. Hwever if your guid rail or slidin ...
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  • 20.9k
1 vote

How to use failure criteria in isotropic material (NASTRAN)

Any NATRAN solution should output the margin-of-safety factors if you output the stresses. Whether they are meaningful for any particular analysis is up to the user to decide, of course. For example, ...
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  • 12.5k
1 vote

mechanical Strength of 3D printed part

This depends on the alloy type (and specific alloy) and the quality of the material after it's been produced which can change depending on the manufacturing parameters. The strengths of additive ...
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