Failure Analysis Of Circular Plate Using Different Material Cards

Failure Analysis Of Circular Plate Using Different Material Cards

ABSTRACT:

The failure analysis of circular plate been carried out by different material parameters (Elasto-Plastic material) which include the analysis of ductile and brittle materials. Then, compared the results as cases by using RADIOSS solver is done.

DESCRIPTION:

MODEL:

• The model is like a circular plate and a rigid sphere. The circular plate is made up of aluminium material and the sphere is a rigid one.
• The model come up with a defined mesh and having the point of impact.
• The study of failure is been carried out by using different material laws like law2 and law27
• By changing the material parameters what would be the result is been analysed and discussed as in a case study manner.

Material properties are:

1. Young's modulus (E) = 71000 MPa
2. Density (RHo) = 0.0028 g/mm3
3. poisson's ratio (nu) = 0.33
4. Yield stress (a) = 290 MPa
5. Hardening Parameter (b) = 562.3 Mpa
6. Hardening Exponent (n) = 0.63

LAW 2 : ELASTO-PLASTIC MATERIAL MODEL (PLAS_JOHNS)

case 1: Law2_epsmax_failure

• This is the given model and the shell properties are edited as per the recommended one to satisfy the real time situation

Ishell=24; Ismstr=2; Ish3n=2; N=5; Ithick=1; Iplas=1

• In the material card, Law=2 (M2_PLAS_JOHNS_ZERIL) is selected
• Density, Young's modulus, Poisson's ratio are already defined
• EPS_p_max = 0.151, maximum strain value in %
• SIG_max = 425, maximum stress value
• The model have failure johnson card which have D - ductile parameters and element formulations are defined.

• The von mises stress is plotted by using hyperview. When the plate stressed by the rigid body it goes upto its elastic limit and then changes into plasticity.
• here, the failure of element takes place when the value of strain exceeds one integration point of the EPS_p_max ,the element gets deleted or cracked.
• Ixfem=0 so the element gets deleted and Ifail_sh=2 so when the stress tensor is set to zero,if the condition reached then elements gets deleted and some are getting crack formulation and the cracks propogate over the longer distance.

• From the energy plot we can see that the external work is done by sphere and circular plate remains the same thats why there is no kinetic energy
• The plate absorbs the kinetic energy and changes into internal energy.
• The maximum increase in internal energy is 27500 joules (absorbed energy) after that element getting removed.

Elapsed time = 128.50 s

No. of cycles = 49480

Energy error = 0.2%

mass error = 0.0%

The energy error is 0.2% because the internal energy is created thats why energy error occurs and there is no mass added to satisfy the energy error thts why its zero mass error.

case 2: Law2_epsmax_crack

In this case, the failure johnson card FAIL/JOHNSON has been modified as

Ifail_sh = 1 (shell is cracked not deleted)

Ixfem = 1 (xfem formulation, failure element cracked)

Dadv = 1 (crack advancement for real time scenario)

In this failure model, when the strain value exceeds the failure plastic strain eps_max=15% its getting cracked. The XFEM and Dadv feature helps to visualisation of cracks formulation. The maximum stress generated is 306.7MPa which is the maximum stress absorbed by the shell. Both the case 1 and case 2 ar more or less same but the failure card determines more realistic crack formulation.

This failure case have increase in internal energy i.e the maximum energy absorbed is 32500 joules.

Elapsed time = 122.99 s

No. of cycles = 49391

Energy error = 3.8%

mass error = 0.0%

Due to energy absorbed by the shell the energy error occurs at 3.8% and the is no mass to satisfy the energy need so zero mass error.

case 3: Law2_epsmax_nofail

In this case the previous model is taken out and the failure johnson FAIL/JOHNSON card have been deleted so we cannot define crack formulation and the optional ductile parameters are also deleted.

In this failure case, the element gets cracked when the strain reaches the max plastic strain value, and the elements are getting cracked and propogate over the longer distance so its like a very poor element formulation property. The maximum stress generated is 270.5 Mpa.

From the above energy plot the maximum energy absorbed by the shell is 27500joules which is same like case 1 and after that the element getting removed. The crack formulation is the major difference in this case.

Elapsed time = 136.02 s

No. of cycles = 49405

Energy error = 0.8%

mass error = 0.0%

The energy error occurs normal and the crack formulation is very poor in this case, there is also no need of mass added to satisfy energy error.

case 4: Law2 with no eps_max value

In this case the previous model is taken out and the EPS_max = 0.4 is been deleted so it takes the default failure plastic strain value as 10^30, which is very high and the material behaves like elastic model. hence, the failure in this case depend upon SIG_max = 425MPa i.e the maximum stress that the material can withstand its limit .

In this failure case, when deleting the EPS_max value ,the failure plastic strain is taken as 10^30 as default so it wont get failure because it depends on the max stress SIG_max value. The rigid body elements are getting intersect with the shell because of maximum stress and the also the material absorbs the maximum stress. If the frame gets one more it will increase the stress so may be some of the elements can be deleted. But the SIG_max value keeps the material behave like an elastic one.

In this energy plot, the shell can can absorb 65000 joules of energy for our time limit as 5ms and its still going on. The material have highest stress it can absorb but when this material is an elasto-plastic, if it behaves more like an elastic material it will repulse the same amount of force that may cause danger to protect the passenger when it uses as an bumper beam.

Elapsed time = 60.39 s

No. of cycles = 48737

Energy error = 3.0%

mass error = 0.0%

The energy error occurs because of internal energy created and the computation time decreases because it doesn't have plastic strain value to calculate failure strain.

case 5: Law1 Elastic material property

In this case, the previous model have been used to convert that into LAW1 elastic model to perform simulation, The density, Young's modulus, Poisson's ratio remain same as it is. The simulation is done using radioss solver.

In this failure case, The elastic material property LAW1 is carried out and it have the highest stress value of 1086MPa and the stress absorption is not that much high than LAW2. Since we didn't apply failure plastic strain so there is no failure elements. This material is not safe for crash analysis.

In this energy plot, the LAW1 elastic material absorbs high energy i.e 850000 joules. The material is very elastic since so it will be bouncy. If we use that material it would just break and transfer force catastrophically to the inside of the vehicle. This material is not safe for crumple zones in the vehicles.

Elapsed time = 126.68 s

No. of cycles = 47969

Energy error = 0.3%

mass error = 0.0%

The energy error increase and then stabilizes as 0.3% because of the internal energy generated in the material because it absorbs energy and repuls back due to LAW1 material property.

case 6: LAW 27 BRITTLE MATERIAL

This law combines an Isotropic elasto-plastic model with orthotropic brittle failure model. The failure or damage occurs only in tension. This material is like a layered one which have glass which is covered by plastic on both sides. This model is mainly used in windscreen related applications.

Material property :

• SIG_max0 = 425 MPa
• EPS_t1 = 0.14 (tensile failure strain at which stress starts to reduce in the principal strain direction 1)
• EPS_m1 = 0.15 (maximum tensile failure strain in principal strain direction 1)
• d_max1 = 0.999 (maximum damage factor in principal strain direction 1)
• EPS_f1 = 0.151 (maximum tensile strain for element deletion in principal strain direction 1)
• EPS_t2 = 0.14 (tensile failure strain at which stress starts to reduce in the principal strain direction 2)
• EPS_m2 = 0.15 (maximum tensile failure strain in principal strain direction 2)
• d_max2 = 0.99 (maximum damage factor in principal strain direction 2)
• EPS_f2 = 0.151 (maximum tensile strain for element deletion in principal strain direction 2)

In this failure model LAW27, the recommended shell properties are modified to get real time reults. There is no EPS_max value so failure of this material is depend on SIG_max value. The maximum stress is 287.3 MPa, this model behaves like an elasto-plastic model but the main aim of this material is brittle. since it satisfied the material need by assigning proper parameters. The failure elements after the defined plastic strain values have been deleted.

From the energy plot, the material behaves like an elastic model but the brittleness property is still there. The maximum energy absorption is 37500 joules, Which seems to be having an good elastic behaviour as well as without compromising the brittleness property. This material model is very safe to be used in Windscreen related applications.

Elapsed time = 68.56s

No. of cycles = 49541

Energy error = 1.2%

mass error = 0.0%

The energy error occurs due to internal energy generated because of the absorption of energy. The computation time is less because the material property is brittle and it have plastic strain value.

CONCLUSION :

The rupture of circular plate, due to the impact of rigid sphere was studied and several failure parameters and different material laws were compared.

• If the model is performed under elastic conditons Law 1 must be an ideal choice.
• If the material is used in front bumper beam, case 2 LAW2_epsmax_crack would be an ideal choice, because it absorbs maximum stress and proper crack propagation.
• If the model is used in windscreen like applications LAW27 would be an ideal choice, because it absorbs maximum energy to withstand stress as well as behaves like a glass and satify its needs.

Law 2 and Law 27 is more or less equal. Each and every material have different property, Choice of material is depend upon the usage of applications under certain condition is analysed by comparing the results.

LINK TO VIEW:

https://drive.google.com/file/d/1FQpoPWZ2gckwuAHyKULyCGRxLsTxJol5/view?usp=sharing