Unfortunately, I was busy at that moment, so I couldn't participate in it. However, now with much more free time, I decided to do it by my own (without any compesation) to show how a small structure design can be done, and to show new engineer students. If I can, I will prepare a video on youtube to show step by step with all the details how I did it.
As the most important point, the company of the challenge made public the requirements of the underrun protector. All the features and requeriments are inside the next pdf file: https://mega.co.nz/#!ONggkC4K!DEhosz1uiOcregHUNwPCTLYPXKk6_LTQAem-wdBcJxQ
The most important points of the requirements are the dimensions, the load cases, the material, and the options that we can do.
The dimensions of the main protection (the beam) are a length of 2500 mm and 100 mm of width. The minimum thickness is 10 mm, but could be more.
The load values are defined by the client in three static load cases of pressure, that are distributed as it can see in the pdf or in the next image.
The first case of load is of 1,25e6 Pa, the second is 2,5e6 Pa and the third 1,25e6 Pa.
The material selected y the customer is a normal Steel with a young modulus of 205GPa, a poisson value of 0,28 and a density of 7870 Kg/m3.
According to the customer, the maximum deformation allow is 40 mm, and the maximum stress value of 355 Mpa. The steel used has a elastic limit point of 200-250Mpa, so the value proposed by the client has sense since it is a protection devide that has to be taking out in case of an impact.
The steel a stress break point around 400 Mpa, so it represents a 1,127 of extra stress, that in my case I cannot be sure since the trucks industry is not my specialty. Taking that the extra value of stress is correct, if not it can be changed, I proceed wit the study/project.
The client also ask that the entire model must be designed in one piece, not as an assembly. The stress study could be done using one online CAE software that in my opinion is not the most accurate; so for this study I will use the CAD software Catia to design the protection, the Abaqus CAE in the Standard mode for the tress/deformation analysis and the software excel fot the mathematical operations.
Other designers during the challenge spent all their resouces in design a "cool" underrun protection. Most of then were designers not engineers, so a "cool" design is more their role. In my case, as an engineer, I prefer center the design in a protection that can resit all the client load cases, with the less material possible, and if it can be the less weight too using just one material, less volume means less weight).
For that reason, my objective is to find the minimum thickness of the beam (according with the shape of the section) that can resist the pressures.
Because start doing designs in catia and analysing with Abaqus until have the correctone would take months, the best way is to use the excel and the material mechanic to make the three load cases and determine the minimum thickness, and then check it using the computer softwares.
The next file is the excel, in which the three load cases are calculated. I compared a normal flat section with a square (empty inside) and this last one, was too strong, so the material wasted would have bee too much.
https://mega.co.nz/#!OA4HXbwS!VfPF-3lwYy9cDr2rGpuMoYUuzNqWt9WspD2WlFzcMNk
After determine the minimum thickness of 45 milimiters, I check the values using a catia model and run it using Abaqus CAE.
As it can be seen easily, if a comparation is done between the excel results and the Abaqus ones, the values are very close, showing that the protection can resit the impacts.
No comments:
Post a Comment