While I was playing pool the other day, I remembered a lesson that I learned during my time at the University of Seville as well as at Cranfield University. It is related to the quite complicated subject of Impact Dynamics… But don’t be afraid, today I’ll just cover a simple case as an introduction. In particular, I’m going to write about how the ideal collision between the white ball and the other ball that we are aiming to move.
First of all, we need to differentiate between different types of collisions, depending on the loss of translational kinetic energy or, in other words, the conversion of kinetic energy to rotations, vibrations or heat. For this case, let’s consider two bodies: one in motion (impactor) and another in stationary conditions. Hence, we can distinguish between the following categories:
- Elastic collision: all the energy is transmitted from one body to another, i.e. the impactor stops and the stationary mass starts moving at the same speed as the initial one from the moving mass.
- Completely inelastic collision: the moving mass stops after hitting the stationary body. The stationary mass remains as it was.
- Inelastic collision: the impactor suffers a decrease in speed after the collision, whereas the stationary mass starts moving at a certain speed.
- Superelastic collision: if additional energy is provided to the stationary body during the impact, then it will start moving at a higher speed than the one at which the impactor hit it.
Let me introduce you to Dr Nicholas Brown, one of the Composite Design Engineers at McLaren Racing and former EngD at the University of Surrey. It was a real pleasure having a conversation with him at the McLaren Technology Centre (MTC) in Woking, UK. We covered different topics about what is like to work at the top level of automotive engineering, including some tips for getting where he is now! Enjoy it!
First of all, I’d like to say how grateful I am to have you here, since I know you are extremely busy at the moment. Thank you for your time and your kindness. And now, let’s get started. Can you tell us a bit about your background?
So I did my masters first in engineering at Loughborough University; that was Aeronautical Engineering. I spent five years up there and did a placement year as well. So my placement year was with an aerospace electronic sort of warfare defense company, but I was doing more of the support work reliability team and things like that, writing general reports… Didn’t really do anything fancy, so I came out of there not wanting to do that and not really wanting to go on a graduate scheme. Then I had a year just between jobs and then the EngD came up, so I chose to do the EngD that as you know is a great opportunity. And then towards the end of it I was looking for more job roles and one came up at McLaren Racing as a Design Engineer, which implied using my composites knowledge for a more applied role. There are research aspects as well, but it’s mainly applying my knowledge. That was about a year and a half ago and now I’m still here! It’s quite fun! It’s good to apply all the things you know. As I said we do research up there but it is completely different to the research I did as an EngD.
Basically, when we want to determine the forces and displacements in a certain structure using Finite Element Analysis (FEA), what we are doing is creating a system of equations that relates the stiffness of the elements to the displacements and forces in each node. When we run a simulation, we do not see all the calculations. For that reason, today I want to illustrate a simple case that can be easily solved by hand applying that methodology.
Before getting started, just think of a spring. Everyone has come across the Hooke’s law at a certain point during school. It states that the force in the spring is proportional to a constant “k” multiplied by the variation in length of the spring. FEA follows the same principle, but in this case the “k” constant is the stiffness matrix and the variation in length is a vector of displacements and rotations, depending on the case.
Let’s study a simple static case. Our structure consists of two bar elements connected at a common node, where a load “P” is applied. The other two nodes have both horizontal and vertical displacements constrained (see the boundary conditions). For this particular case, the reactions in nodes 1 and 3 and the displacements of node 2 are requested. I have solved the problem by hand following a few steps that, based on my experience, can be generalised for more complex problems. Pretty much, the summary of the methodology is: Read more
Last February I participated in the Young Persons’ Lecture Competition, organised by IOM3. In particular, the local heat took place at the University of Surrey. I want to share with you the transcript of my presentation. I have to say that I tried to present a quite complex topic in a very simple way so that anybody without an engineering background could follow it. Hope you enjoy it!
Abstract: What would happen if you removed the roof of your car? First of all, you would have a convertble vehicle to enjoy that one sunny day we have in England. Second and most importantly, you would probably be the bravest person on earth. Driving on a bad road or even going over a speed bump could have dramatic results. Using simple engineering concepts, logic and a shoe box you will be able to understand why that could happen ad how automotive companies overcome this issue.
Let’s start from the beginning. What is Strength of Materials? It is the science that studies the behaviour of solid objects when they are subjected to stresses and strains. So, first question: what kind of objects? Basically we can have 1D, 2D and… Exactly! 3D elements! Some examples could be a bar (1D), a shell or a plate (2D) and a hexaedron (3D). For this particular topic, I’m going to focus on 2D elements, since the body panels of a car can be considered as very thin shells assembled together.
Although the performance of lithium-ion batteries (LIBs) have been remarkably improved in the past decades, there is a big risk in the use of this type of battery: they can catch fire when they are subjected to abuse. Researchers from Stanford University have developed a nanocomposite material which can be included into the electrodes in order to prevent the explosion of the battery.
To perform in an efficient way, LIBs require operation conditions which are within a specific range of current density, voltage and temperature. Nevertheless, when they are subjected to abuse conditions, exothermic reactions can take place, leading to a fast increase in internal temperature and pressure. What does it mean? Well, our battery is likely to explode!
Current LIBs include external sensors to prevent overheating and overpressure but, unfortunately, temperature and pressure inside the cells can actually increase much faster than they can be detected by those external sensors. Because of that, several alternatives have been developed in order to include internal components to solve the problem. For example, ceramic coating has been proven to be an effective way to shut down the battery and improving the thermal tolerance. However, after the battery is shut down, it cannot be used again. Using solid-state electrolytes can be another option, but the overall performance of the battery is decreased due to their low ionic conductivity. Read more
A while ago, I wrote a simple document for undergraduates in order to explain that composite materials can fail in different ways. This was created as a high level document which could be used to find useful references with regards to failure modes, basic failure criteria and damage propagation models. I wanted to share this with you in case you are new in this field or just if you simply want to learn some basics of composites!
A composite can be defined as a material which is composed of two or more constituents of different chemical properties, with resultant properties different to those of the individual components. They usually consist of a continuous phase (matrix) and a distributed phase (reinforcement). These reinforcements can be fibrous, particulate or lamellar and they are usually stiff and strong, so that they are responsible for providing the stiffness and the strength of the composite. On the other hand, the matrix provides shear strength, toughness and resistance to the environment.
Fibre reinforced composites are considered as the strongest and sometimes also the stiffest, due to:
- Alignment of molecules or structural elements.
- Very fine structures.
- Elimination of defects.
- Unique structures.
- Statistical factors.
With regards to fibre reinforced composite materials, their main failure modes are:
- Fibre failure induced by tension in fibre direction.
- Fibre failure induced by compression in fibre direction.
- Matrix fracture induced by tension.
- Matrix fracture induced by compression.
It is remarkable that fibre failure typically caused composite failure, whereas matrix failure may not cause the same drastic effect. Read more
After a relatively long period of instabilities, the Spanish composite manufacturer Carbures is raising again. This is really good news for the Spanish industry and for all those engineers who are interested in this kind of advanced material.
It’s just been made public that in 2016 Carbures reached their historic record in terms of the production of aircraft components made of composite materials. As a matter of fact, their production has increased 16.2% with respect to 2015, manufacturing a total of 45,695 aircraft parts. Therefore, we can say that Carbures have returned to the place where they belong: being one of the top composite manufacturers for the European aerospace and defence sectors.
For those who don’t know the company, they produce structures for quite a few members of the Airbus fleet. For instance, some of the civil airplanes which use their components are: A320, A320NEO, A330, A340, A350 or even the impressive A380. In addition, they also contribute to the military sector (e.g. A400M). The parts which are manufactured by Carbures include from lids of the oil tanks of the engine to parts of the fuselage. Read more