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Designing the Perfect Bra?

Finite element analysis and a high isotactic polypropylene homopolymer....

Assembled from material supplied by Ove Arup and Partners' Advanced Technology Group, Charnos, PPD and SMP Multi-Shot Ltd

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The search for a bra with a perfect fit has been made by many women over the years. However, until recently there has been little application of engineering to bra design, despite an early patent brought by an aeronautical engineer. In fact, the basic design has not changed dramatically since its appearance in 1885. But now a brand new design of bra has been released.

The Designers

London-based industrial designers, Dick Powell and Richard Seymour, were asked by a TV show to attempt a radical redesign of the bra. They were assisted during the project by the consulting engineers, Ove Arup and Partners' Advanced Technology Group, who by using sophisticated computer modelling software were able to give an insight into the engineering performance of the bra using advanced computer techniques.

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The recent interest in bra design has been prompted by the fact that average breast size is getting bigger - the average size has increased from 34B in the 1950s to 36C today.

Modern bras, which are mostly designed from a fashion perspective to look flattering, are unable to provide the necessary support. Comfort is also an issue. A study by Nottingham Trent University showed that 70% of women were wearing a bra that doesn't fit properly. Either women cannot find sizes to fit them or the bra size alters with wear and washing.

The problem for manufacturers is then to produce a bra with the necessary support and fit, with no loss of performance over time, which is attractive to the eye and is capable of all of this in a wide range of sizes.

Non-Linear Finite Element Analysis

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The role of Arup's Advanced Technology Group in assisting Powell and Seymour in this difficult task was to assess the performance of the existing bra design. Louise Waddingham, who undertook this unusual analysis task noted, "The group is used to advising a wide range of designers, engineers and manufacturers and specialises in using advanced engineering methods in the vehicle, nuclear and seismic engineering industries."

In this particular case, the Arup engineers used dynamic non-linear finite element techniques to analyse the bra's structural performance. A computational representation of the bra on a body was created by scanning the geometry of a model. The bra was then constructed using techniques usually associated with the modelling of airbags and seatbelts in cars. This enabled the non-linearity of the bra material, contact interaction with the body and large displacements to be represented.

The performance of the bra was then analysed by applying vertical accelerations to simulate a person jogging lightly or walking briskly. The analysis displayed fluctuating stresses in the bra cups and straps, varying with the walking pattern, and a higher constant stress around the base band where the bra was pulled tight onto the body.

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More interestingly, the behaviour of the underwiring was revealed. As manufactured, the underwiring is a two dimensional form. When being worn, the wire undergoes bending in two directions. It is bent around the body as the bra is put on and also bends in the other direction as it supports the weight of the breast. In addition, the axial forces along the length of the wire are significant in its tendency to pop out of its casing after repeated wear.

Quoted in Time magazine, designer Dick Powell says bras are more complex than he first imagined. Larger breasts tend to want to go "east-west, while bras want them to go north-south," he explains. "The resulting force causes a fairly considerable amount of rubbing and irritation."

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Seymour and Powell focussed on the inefficiency of the underwiring and in their bra design they replaced the wire with 'Bioform', a large plastic moulded support that extends to the underarm area. They suggested that the Bioform bra fits all the requirements of support, comfort and washability as well as adapting across three sizes at once.

In fact, their ideas were received well by Charnos, a leading bra manufacturer, which decided to put the Bioform bra into production.

Productionising the Design

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The innovation of the new bra is in the unique, three-dimensional undercup support component which does not contort or distort the breasts, but simply shapes and supports in the most flattering, comfortable way, especially for fuller cup sizes.

A structure inspired by an aerobie, the essence of Bioform is a 2-shot moulding process where the inner core or armature replicates the underwire, but is infused in a softer polymer that holds and shapes the breasts. In more detail, the cup is made from a soft, body-forming polypropylene TPE, specially formulated by Krailburg, supported by a high isotactic polypropylene homopolymer from Solvay.

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A prototype 2-shot tool of a mid-range size was produced to enable moulding trials of the shortlisted materials to be evaluated in wearer trials. Having optimised one size in the range, a Finite Element Analysis (FEA) study was conducted to refine the structural performance capabilities of the other sizes in the range. The results of the FEA study gave Charnos the confidence to commit to the seven sizes of production tooling.

It was recognised that twin-shot moulding would be the most efficient production method for the novel insert. It would also ensure that the two materials would create a single, inseparable component - one of the most common problems with the traditional design was the underwires detaching in the washing machine. Extensive wear and washing trials were conducted to ensure that similar problems did not occur with the new insert.

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The Bioform eliminates the 'Ouch Zone' - identified by Seymour and Powell (and millions of women) as the problematic area under the arm where underwired bras dig in and pinch the flesh - and has been designed to withstand machine washing.

The beauty of the Bioform is that any fabric can be stitched to its unique polymer form, which means that as Charnas expands the range, Bioform bras will be available for both everyday wear and occasion wear, with a Bioform moulded t-shirt bra set to follow the 'original' design very soon.

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The Bioform range was launched last year in leading stores in the UK and USA. Commenting on the launch success, Tony Hodges, MD of Charnos said, "Sales of Bioform have exceeded the expectations of ourselves and our retailers. Bioform has become the Number One selling bra in those outlets lucky enough to have it."

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