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Shock analysis using Solidworks simulation 1

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lcatg

lcatg

Mechanical
Oct 7, 2015
41
Hello,

I am doing a Shock analysis of Pump using Solidworks simulation. attached are the shock load input(Full sine wave) and Max stress plot at a node. My doubt is the peak load(+) is at 0.01 secs but the max stress is at 0.02 secs at which the amplitude is zero. Is that correct?

Is there any relation or formula saying max stress should be at the time of peak load? Pls clarify.
 
 http://files.engineering.com/getfile.aspx?folder=85bc62f9-d48a-4e2d-8ab3-62dc7d51e921&file=load_and_stress_plot.JPG
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I have not opened the attachment. The peak stress will occur at peak strain. Strain waves take time to travel through the structure. The speed at which they travel is not simple, in general, but is strongly related to the modes which have been excited.



Cheers

Greg Locock


New here? Try reading these, they might help FAQ731-376
 
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Hi GregLocock, thanks for the response.

as you said, peak stress occurs at peak strain which is,in my case, exactly at 0.02 secs. So is there any relation between this stress/strain w.r.t time? why not at some other time say 0.035 secs? I googled to find, but didnt get anything related.
 
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Greg answered your question already: "Strain waves take time to travel through the structure. The speed at which they travel is not simple, in general, but is strongly related to the modes which have been excited."

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Peak stress lags peak acceleration, sounds ok.

I'd be more worried if it were the other way 'round.
 
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A likely upper bound for the speed of strain transmission is given by the square root of E/rho, but for say a car body the speed is more like 60m/s.

Cheers

Greg Locock


New here? Try reading these, they might help FAQ731-376
 
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Exactly, root E/rho is the speed of compression waves (axial waves). Most modes in structures are bending waves, which are much slower.

It would be interesting, and possible, to look at real world test data on this. The concepts are loosely associated with structural intensity, analogous to acoustic intensity. The non quadrature part of the energy in the mode is actual energy being transmitted.



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Greg Locock


New here? Try reading these, they might help FAQ731-376
 
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In steel that's about 6000 m/s. Typical muzzle velocity for a battleship's rifles firing AP shot is 762 m/s. So there must be other mechanisms in some cases.



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Greg Locock


New here? Try reading these, they might help FAQ731-376
 
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There is, since there's sheer kinetic energy or explosives. I was specifically referring to EFPs, as there was, and still is, to some degree, some uncertainty as to whether penetration by EFPs, particularly the pointy ones, is due to melting of the armor or some other mechanism. There's still information out there that states that EFP projectiles are essentially like hot lances, but it's unclear whether there's sufficient thermal mass to melt armor, particularly if it's composite armor.

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AP shells have a hardened cap that in theory remains in one piece during the entire penetration. Not surprisingly the poor control over heat treatment in WW1 caused a significant number of shells to shatter on impact. Nonetheless Campbell's book includes many photos of holes punched neatly through 12" plate.

here's the sort of thing


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Greg Locock


New here? Try reading these, they might help FAQ731-376
 
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Sure, but you have to compare that against same AP shell just pushing on the armor. Under those conditions the armor will distort and possibly fracture before you could get any sort of hole in it. Moreover, some EFPs use copper, which is hard, particularly since it's work-hardened in the process of forming the projectile, but not harder than Chobham armor, and yet, there are M1A1s with holes, but not necessarily through holes, in their armor from improvised EFPs.

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