MATERIAL

The Nitinol (Nickle 51% + Titanium 49%) is a shape memory alloy which can be programmed to take a certain shape at actuating temperature which is called the austenite state ranging from 45-85⁰C. This smart material possesses a great load carrying capacity when it is transforming back to its programmed shape on deformation. This capacity of pulling weights on activation was explored in series of experiments to understand the potentials of this material for use in architectural scale.

OBJECTIVE

The aim is to study the materiality and behavior of Nitinol with the actuator of heat, and design an architectural application using the properties of expansion, contraction and weight bearing strength from series of investigations to control a responsive building façade system, dependent completely on passive heating techniques.

TESTING STRENGTH CAPACITIES OF ZINC AND NITINOL SPRINGS

In the T1 test series of experiments, standard zinc springs are put through series of investigations to find their spring constant and degree of expansion and resistance. The T2 test series of experiment is performed on the Nitinol spring to understand its weight bearing capacity and pulling strength on heating.

TESTING NITINOL-ZINC SPRINGS IN SERIES

The results of T1 and T2 are used in test series T3 to couple the zinc and Nitinol together to find a match between the 2 springs. This creates a loop movement on expansion of either spring.

Conclusion: In cold state, the strength of Zinc spring must be a little more than Nitinol spring. Nitinol on heating pulls the zinc spring due to its high capacity of pulling weights while nearing austenite and the zinc contracts to expands Nitinol spring on cooling. This loop of linear expansion of springs is performed at every change of temperature above and below actuating temperature of Nitinol. The length of each spring is crucial in determining the displacements between springs used to mobilize the kinetic system.

Best result obtained a movement of 34% expansion of the length of joint.

DESIGN OF JOINT

The joint are designed with 20mm Nitinol spring and 40mm zinc spring connected in series. The central point of connection of springs is mobile which slides in either direction while the ends are constricted. The Nitinol in martensite is stretched by the zinc spring to maintaining equilibrium of forces. On actuation by heat or electricity, the Nitinol contracts, displacing the central piece which lengthens the joint by 34mm in a 100 mm joint. On completion of one loop, the displaced point returns to original position. Different lengths of springs are studied to obtain maximum displacement.

APPLICATION SYSTEM 1

The capacity of Nitinol-zinc joint to displace objects is studied on fabrics. Stretched fabrics possess resistance which is combined with the resistance of zinc to determine the lengths of each spring to perform the loop. However the displacements observed in the experiment is minimal and not efficient for architectural scale.

APPLICATION SYSTEM 2

The Zinc spring which creates a counter force to pull back Nitinol spring in the joint is replaced by elastic metal ring in order to be embedded in a specific shape. Nitinol spring is planted on the diameter of this ring. On heating, the Nitinol contracts, thus deforming the ring under high tension and is stretched back by the tensed ring once the spring cools down. This displacement caused by deformation of ring is coupled with stretched fabric to initiate a kinetic system. The best result obtained in this joint was 40mm in one direction with Nitinol spring of 20mm and resultant displacement of 4 springs in different direction is 88mm.

Objective: Design a structural and self-assembling structure from a two-dimensional, flexible material like fabric

Topic: Responsive structural behavior based on the properties of pre-stretching of fabric

Description: Our research was initially inspired by the Programmable Textiles project of the Self-Assembly lab of MIT. The objective of this project was to program pieces of textile to deform in a specific way after patterns had been 3d-printed on them at a pre-stretched state. The objectives of our research are to understand the mechanisms through which these deformations occur, to add interactive elements and to explore how a structure of these principles could be applied in architecture.

At the first stage, our research was focused on the deformations that occur when simple patterns are being 3d-printed with certain filament on stretched lycra fabric. The conclusions extracted from this stage are important for the form-finding of our final structures in a bigger scale.

The next step of our research was to define a way to enlarge our structures. The PLA filament we mainly used for the 3d-printing is a typical thermoplastic material, meaning that becomes pliable or moldable above a specific temperature and solidifies upon cooling. This way, when the prototypes are heated the printed pattern becomes less stiff and at the same time the forces of the stretching of the fabric prevail and the deformation becomes more intense. Except if an external force is applied, the pattern becomes stiff again when cooled in a new position.

Following this principle, among the heat-responsive polymers we think that the shape memory polymer could have a lot of potential for the further development of our project. Changing the stiffness of the material by heating, in the desired places would offer us control over the form of the structure in a much larger scale.