test di caduta (solidworks simulation)

[Spa]

Hello everyone!!!! I've been following you for a few months and last week I finally decided to join you. I am currently working for university in a company that produces aluminum containers. My task is to simulate the fall test from a certain height and check if the component holds impact. in case the component does not hold it will be necessary to optimize the structure. I looked a lot on the forum but I didn't find anything about fall test. If there would be someone willing to help me I willingly expose my problems.....that maybe for some of you are banality but for me that are the first approaches with simulations are serious problems!! thanks to everyone in advance!!!! Have a good day! !

 

[Matteo]

Hello and welcome.

the forum works like this: you put a complete description of your problem with images and specifications, so that you can help and at the same time enrich the forum... you will see someone who helps you find him

in case geometry or problem is "reserved" you can always spend a few minutes preparing a "simplified" but significant problem to propose to the forum.

 

[Spa]

Thank you for your advice! You did well to tell me because being new I still don't know how to move. :smile: to explain to you in a simple but understandable way my problem, you could consider the container as a rectangular case made of sintered aluminum (en 46100). the first problem concerns the type of model to be inserted in the properties of the material (plasticity - von mises or isotropic linear elastic). the stress curve - deformation of the material is not there and I couldn't find it anywhere!!! if I consider the properties of aluminum I should consider the plastic model but... doing a practical test I saw that the break is like that of fragile materials (the fracture is perfectly recomponed). looking at the results those that approach more to reality are those obtained using the model of plasticity because with linear elastic analysis gives me exaggerated values. is it correct to consider a plastic model when the fracture tells me that the material is fragile??? What model should I use?? I trust you!!!! :smile: thank you in advance to those who will answer! ! ! ! !

 

[Spa]

Any advice???? any idea?? ?

 

[SOLID]

looking at the results those that approach more to reality are those obtained using the model of plasticity because with linear elastic analysis gives me exaggerated values.

if you do a linear analysis could be "normal" that excre voltage values higher than the breaking load, since there is a direct proportionality between deformations and tensions.
if instead impose a non-linearity in the material you will certainly get some tension values closer to reality (of course always taking into account the type of mesh, etc...)

is it correct to consider a plastic model when the fracture tells me that the material is fragile? ? ?

You're messing around here. even if the material is fragile you can safely use a linear model in the material.
the important thing, instead, is to choose the right criterion of breakup.
Usually for fragile materials (e.g. cast irons) I go to evaluate the critical areas by plotting the main sigma, while for ductile materials the von mises.

 

[Spa]

Thank you so much solid!!!! If I have not understood badly then until I am in the elastic zone of the stress strain chart use a plastic criterion or an elastic one is indifferent. what changes is beyond the stress of yielding where the two criteria have different behaviors.. Right? So when considering a fragile material the two criteria should give the same results??? ? I have always looked at the tension of von mises... but from what you are telling me I always wrong!!! in the coming days then I will try to plot the main tensions. but...not having the stress deformation curve I should consider the maximum tensile tension equal to that of compression or should I consider them different??? ? Thanks again for your help you were really too kind!!!!! Good evening! ! !

 

[SOLID]

If I have not understood badly then until I am in the elastic zone of the stress strain chart use a plastic criterion or an elastic one is indifferent.

It always depends on the goal you have to achieve.
I'll give you a practical example.
If you need to check a transmission box you just need to create a linear model of the material, because your goal is to verify the behavior in the elastic field. any tensions higher than yielding (naturally to check case by case) are to indicate that the material has deformed plastically, and therefore geometry and type of material do not have the requirements to endure those loads.
While if you have to evaluate the energy absorbed by a protective structure for example in a rops or fops test, you must absolutely adopt the characteristic curve of the material and go to evaluate the deformation energy that must be compared to the applied one, without the structure coming to the collapse (so that your max sigma, is not superior to that of breaking).

what changes is beyond the stress of yielding where the two criteria have different behaviors.. Right? So when considering a fragile material the two criteria should give the same results??? ? I have always looked at the tension of von mises... but from what you are telling me I always wrong! ! !

then the resistance criteria you use according to the type of material you have and your experience.
while shaping or not the non-linearity of the material you do it according to what I told you before

but...not having the stress deformation curve I should consider the maximum tensile tension equal to that of compression or should I consider them different?? ? ?

definitely with the von mises you do not know if the material is working in traction or compression.
While if you plot the main sigma you know if you are working in compression or traction based on the sign.
generally the compression breaker is greater than the traction.
If you want to approximate the elastoplasty behavior of the material you can do it for example with a perfect elastoplasty curve

 

[Spa]

thank you again for the precious advice!!! :Smile: if I have understood so if I want to see what is the maximum height from which my object can fall without undergoing a plastic deformation or a breakage I can perform a linear analysis by failing the main maximum tensions....right? and tangential tensions.... how do I consider them??? If I suppose the maximum compression voltage is double compared to the traction voltage (being a fragile material) is an acceptable approximation?? ? Thanks again for the huge help you're giving me!!!! !

 

[SOLID]

If I have understood so if I want to see what is the maximum height from which my object can fall without undergoing a plastic deformation or a breakage I can perform a linear analysis by failing the main maximum tensions....right?

during a fall test substantially the potential energy of the object (mass*fall height* gravitational acceleration) is transformed into deformation energy which, in an elastic linear analysis, is 1/(2e)sigma^2 that integrated throughout the volume gives the total deformation energy. Naturally neglecting all the dissipative effects.
So if there are tensions higher than that of yielding it means that part of the potential energy has deformed your component.

and tangential tensions....how do I consider them? ? ?

do not consider them ( fragile material) so take the main ones of the tensor of the efforts.

If I suppose the maximum compression voltage is double compared to the traction voltage (being a fragile material) is an acceptable approximation? ? ?

usually compression efforts do not create problems, always if you do not consider elastic instability.

 

[Matteo]

grand solid :finger:

 

[Spa]

Sorry to bother you but...I'm still here with a new doubt!!!! my material has a yielding voltage of about 175 mpa, a breaking voltage of 280 mpa a maximum stretch of 2% and young module of 76000. If I have to find the height from which my object breaks, my idea is to make various simulations with different heights until I get a main voltage value that is equivalent to my breaking value...how can reasoning go? I ask you because if I don't remember badly I had read that during the shock you can present instantaneously also voltage values much greater than the maximum without leading to break the object. during a fall test so is there any particular consideration to the maximum voltage or is the nominal value simply evaluated? in simulations now I am using a plastic model and I am analyzing the maximum voltage (as suggested being fragile material)!! thank you again!!!! good day! ! !

 

[SOLID]

My idea is to make various simulations with different heights until I get a main voltage value that is equivalent to my breaking value...how can reasoning go?

I would keep on the value of yield

Perhaps I am wrong, but I would like to make an observation.
standardized tests with which the stress-deformation curves of materials are evaluated are carried out at fairly low speeds.
in the shock, however, this speed is very high and the crystalline structure of the material fails to deform in time and you will break in the elastic field, however surely at a higher value than the nominal yield voltage.
Are you referring to this?

I ask you because if I don't remember badly I had read that during the shock you can present instantaneously also voltage values much greater than the maximum without leading to break the object.

Then

in simulations now I am using a plastic model and I am analyzing the maximum voltage (as suggested being fragile material)!!

I'd like to clarify something.
if your falling object deforms permanently without breaking has passed the test?

 

[Spa]

hi solid!!! I am pleased to have found someone to confront with this topic!!

Perhaps I am wrong, but I would like to make an observation.
standardized tests with which the stress-deformation curves of materials are evaluated are carried out at fairly low speeds.
in the shock, however, this speed is very high and the crystalline structure of the material fails to deform in time and you will break in the elastic field, however surely at a higher value than the nominal yield voltage.
Are you referring to this?

Sorry, but I didn't understand the reasoning. ..how does it have a break in the elastic zone and however to be at a voltage greater than that of yielding?? i.e. if it is above the yielding voltage how can it still be in the linear zone??? What a mess I have in my head!!! :redface: looking here and there I found graphs that show that tensile strength increases with increased load application speed. therefore in theory the more force is "impulsive" the more tension of breakage will be elevated. Right? ?

I'd like to clarify something.
if your falling object deforms permanently without breaking has passed the test?

So, my idea is this: first I wanted to find the height from which my falling object comes to break (taking as reference the breaking voltage) and then I would have liked to find the height from which my object can fall without deformation (and in this case I would have checked that the main maximum tensions are all below the yielding voltage). is it wrong as reasoning?

 

[SOLID]

how does it have a break in the elastic zone and however to be at a voltage greater than that of ridding? ?

attention I told the value of the snervamento nominal, but it is my hypothesis, based on my reasoning.

looking here and there I found charts that show that tensile strength increases with increased load application speed.

Could you lint these charts, so I refresh my memory?

then I would have liked to find the height from which my object can fall without deforming (and in this case I would have checked that the main maximum tensions are all below the yield voltage). is it wrong as reasoning?

in the elastic field you could do so

surely there is a law of proportionality between the fall height (soever the potential energy) and the square of tensions, in the field exclusively elastic.

make a first simulation by assuming a certain fall height (which I will call z1) and find the maximum value of the main sigma (which I will call sigma1).


so do this limit height =z1/sigma1*sigma snrv. nominal

In this way you can find the limit height beyond which you exceed your reference sigma.

 

[Spa]

ok...to find the height from which it falls without deforming being in the elastic field I would say that it should be "low" simple. I apply the proportionality that you rightly quoted and "in theory" I find the limit height. My real problem however is to find the fall height to which the object breaks. Since the impact can be seen as the application of a dynamic load how do I consider the nonlinear part of the stress deformation chart?? what voltage value do I consider as maximum value??? Do I consider the value of the limit voltage equivalent to that of breakage or should I stand on a lower value?? or maybe a taller??? ? similarly you could think about stretching: how much lengthening can the material stand before coming to break being a dynamic and not static load???? I could ask you a thousand more questions.
one of the graphs I told you about is this:
http://dma.ing.uniroma1.it/users/veniali/materiali_2.pdf save the slide 38

buona serata!!! !!!

 

[SOLID]

Since the problem is quite complex, you can begin by simplifying it using a bilinear curve where you will insert the voltage values to break and to nominal yield.

I don't know if you can do it, but once you correctly set the model you could perform an optimization analysis, where the bump to optimize is the fall height according to the stress in the material). . .

Good job!

 

[Spa]

Okay....now I will try this way too!!!! and....in case of need....I will know where to find you!!!! good day!!!!! and... thank you again!!! !