Magnetic Fields to Aid the Manufacturing of hi-performing Composites

Bradley Mee has spent his Wolfson bursary in our lab developing a novel method to align reinforcing fibres within a polymeric matrix using magnetic fields. In this way, the mechanical properties of the composites can be tailored for specific applications and load requirements.

In his final report he wrote:

“Polyurethane composites are widely used due to their strength and light weight-ness, as well as the low cost and scalability in production. The PU material comes in two separate liquid chemicals that once combined in equal amounts rapidly expand to 200% of the original volume and cure hard, taking the shape of the mould it is placed in. There is an opportunity to shape and further increase the strength of these parts by forming a composite of PU and carbon fibres (added in the liquid/expanding stage), with localised reinforcements. It has previously been shown that these composite materials produced increase stiffness in both tensile and compressive testing.

The aim of the project is to test the hypothesis that [a magnetic field] aids the alignment of carbon fibres in a certain direction and will increase the strength of the material, compared to randomly located fibres. To achieve this; firstly, a literature review of electromagnetism and permanent magnets was carried out. Secondly, finite-element software was used in order to create a model of the problem and to visualise the magnetic fields created by the magnets. These two objectives provided the basis for a prediction on the direction and alignment that magnetised carbon fibres. Thirdly, lab-based experiments were carried out using a magnetometer to measure the actual magnetic field strength in air. The results were compared to those of the computer model and confirmed to be congruent. Finally, composites were produced in a bespoke mould and the specimens underwent mechanical testing.”

Bradley in the lab during sample production

Bradley has returned to his Electrical and Electronics Engineering studies and is aiming to pursue a career in the aerospace where these high performing composites could be in use in the near future.

Enhanced mechanical performance of lightweight polyurethane foam reinforced with a low content of aligned magnetised short carbon fibres

Our latest work for the manufacture of reinforced cellular polymeric structures is out now. We used a hybrid manufacturing process using insitu magnetisation of carbon fibres that then could be guided, oriented and positioned to those areas of the reacting polymeric core where reinforcement was most needed. In this study we found out that:

• It is possible to attach magnetite nanoparticles to carbon fibres via a facile electrochemistry route, quick and suitable for mass production
• These magnetised fibres can be aligned in a structural foam such as a rigid thermoset (polyurethane) foam using a relatively weak source magnetic field
• The tensile mechanical properties are improved with content loading as low as <0.4%vol, making this approach economic for the manufacturing industry of lightweight composites.

The paper can be accessed at the Composite Interfaces Journal via Taylor & Francis Online.

For a full description of the work and sponsoring bodies, visit this page.

Engineered foams for wheelchair seating

We have published the results arising from our studies on open cell polymeric foams that can be tailored so that they support those who are bed bound or wheelchair users providing them with general well being and alleviating pressure points.

Avoiding pressure points, managing sores and permitting air permeability are the three main design specifications that clinicians aim to when choosing a cushion. In addition to that, a functional cushion, such as those who support lateral movements (e.g. leaning sideways to grab a glass of water and be helped to return to your initial position without compromising one’s stability) and protect from vibration and impacts (e.g. dropping off a curb), are the focus of our research project.

The Multifunctional Materials Lab and clinicians from the NHS have studied how we can help their clinician colleagues understand cushion performance and therefore aid them with the prescription of these to patients and users.

The results from our study have been published in the Medical Engineering and Physics Journal and in the Assistive Technology Journal .

The International Standard that regulates developments in this topic is the ISO16840-2:2007, which is currently under revision. We are hoping our work to inform their work and assist in their revisions for the replacement ISO 16840-2.