Special shape memory alloys are showing a reversible structural phase transition. This transition can be introduced by increasing temperature or stress.
In the shown example it is introduced by stress (force) which can be nicely seen in the hysteresis in the force – displacement graph.
Force displacement graph with 2 cycles showing the hysteresis with constant displacement and force rate
While applying stress with a constant stress (force) rate, the control loop of the electronics needs to handle the abrupt change of the stiffness of the sample. Once the transition is in place any further displacement of the sample doesn’t induce any increasing force reaction of the material.
For a constant stress rate the machine needs to rapidly increase the speed to achieve the set stress rate without overshooting or oscillating.
Same cycles showing force and displacement over time
These tests have been performed during our testXpo together with Dr. Eduard Vives from the Universitat de Barcelona. Many thanks to him for contributing the samples to us and helping us to find the proper settings on our machine.
For further information to the related materials see the references:
E.Bonnot et al. Phys. Rev. B 76, 064105 (2007)
E.Bonnot et al. Phys. Rev B 78, 094104 (2008)
E.Vives et al. Phys. Rev. B 80, 180101 R (2009)
E.Vives et al. Phys. Rev B 84, 060101R (2011)
30 students from the TU Freiberg came to Zwick as part of a one week student excursion. The students are mainly in master courses from different faculties like machine engineering or materials science.
After a short introduction of Zwick we have shown different machines and applications with static or dynamic loading.
A group of 12 students have visited Zwick during a study trip to Germany.
The Montanuniversität Leoben is located in Styria Austria and has his founding back in the 19th century. Founded as a University of Mining it has developed more and more expertise in the field of an Technical University.
The students are from the department of Mechanical Engineering. Zwick was part of their excursion to the University of Stuttgart, Wieland, Kuka just to name a few.
We had a very interesting afternoon together with many questions regarding Zwick and Materials Testing.
We are looking forward to welcome more students at our facility to exchange ideas.
Zwick was delighted to welcome delegates to their 4th Academia Day inManchester, which was organised in collaboration with theUniversity ofManchester. The event comprised a Seminar which focused on the topic; ‘Materials in ChallengingEnvironments’ and the presentation of the Zwick 2012 Science Awards.
The Seminar attracted distinguished speakers from Universities in theUKandGermanyand interesting presentations ranged from the challenges encountered by materials employed in Nuclear Power Reactor Systems to the Mechanics of Materials at High Temperatures.
A highlight of the event was the presentation by Dr Jan Stefan Roell, of the Zwick 2012 Science Award and Paul Roell Medal. A total of 73 outstanding entries had been submitted for the 2012 competition and from a shortlist of 10 papers the 3 winners below were selected.
Michal K. Budzik from the Université Bordeaux 1, France. “Instrumented end notch flexure – Crack Propagation and process zone monitoring Part II: Data reduction and experimental”
Angelica Segovia from the Universitat Politècnica de Catalunya, Spain. “Essential work of fracture analysis of the tearing of a ductile polymer film”
Pietro Carrara from the Università degli Studi di Firenze, Italy. “Shear tests of carbon fibre plates bonded to concrete with control of snap-back”
During a visit of a Prof. Lu from Nanjing at Zwick in Ulm we could successfully connect his new design of a biaxual clip-on extensometer to our testControl system. The clip-on comes with one axial and 2 transverse channels to measure the elongation and reduction in diameter on round samples at the same time.
Made and designed by his students he wants to connect this clip-on to one of the Zwick machines in his lab in Nanjing. One of our engineers connected the 3 strain gage channels with 3 universal connectors to our testControl and after some small adjustments in testXpert® II, like the amplification, the measured path of the clip-on was equal with the moving crosshead of the machine while using a split sample.
Superimposed display of the moving crosshead and Clip-On signal in testXpert® II
Now Prof. Lu can demonstrate the “new design” to his students on one of his Zwick machines.
This is just another impressive example of the flexibility of our testControl electronics.