Research in Engineering Education Symposium 2011 - rees2009

Universidad Politécnica de Madrid (UPM) Página 730 de 957
second step would imply the development of two additional virtual experiments for the
next academic year. The choice of such experiments, besides their scientific interest, which
will be commented later, is based on the relatively complex preparation of the specimens
(for the case of dislocations observation) or the long time required for the tensile tests
(several specimens tested at different strain rates and temperatures), which make these
experiments in its classical version available only to a reduced number of students. This
was the case in which both experiments were first introduced for at our University
(academic year 1997/98, for a group of 15 Master’s degree students).
On the one hand, understanding dislocations is a key issue for students of Material Science
and Engineering. Dislocations are crystalline line defects which are responsible for the
plastic deformation of a crystal. There is a complex phenomenology involving dislocation
creation, dislocation dynamics and annihilation, which in turn are crucial in order to
understand the hardening mechanisms in metals (Hull & Bacon, 2011). Moreover, it is
highly desirable that students be familiarized with microscopy and the observation of
micrographs already during their first year at university. On the other hand, tensile tests,
being the most common mechanical tests, are central to the formation of future engineers.
In particular, tensile tests on polymers (PMMA) can shed light on phenomena such as glass
transition, necking and strain localization, crazing and micro-cracking, to name but a few
(Ramos-Carpio, 2007).
Methodology
First, students are provided with an experiment guide containing some of the theoretical
foundations and the experiment procedure together with the key questions that at the end
should been answer in a final report they must complete. Some additional material such as
pictures and related bibliography is included. This point is relevant because the
information contained in the experiment guide is not complete, so each group of students
is encouraged to conduct their own research on the suggested issue.
A video is recorded and edited by the teaching staff. In the case of dislocations, this video
begins with a general introduction to the experiment and continues with a step by step
development of the practice, where a monocrystalline specimen made of NaCl is prepared
and a Vickers indentation is performed on it. The video is embedded in several parts
inside a PowerPoint file. This file also provides a complement to the theory with images
and numerical simulations on dislocation dynamics. The students can download it during
a certain period of time. Customized experimental data is generated by an algorithm
through a scaling parameter based on the students’ personal code. Among these
customized data, a magnification number is attached to an array of micrographs, and
students are asked to measure elements such as the distance between surface steps,
indentation footprint size or the density of dislocations in a certain area (see Fig. 1). The
methodology is identical for the tensile test on PMMA. Here, the scaling parameter is used
to generate a file containing the specimen dimensions, cross-head displacement,
extensometer measurements and load. Students are asked to obtain the nominal and true
stress-strain curves and to describe the deformation and fracture mechanisms from
pictures (Fig. 2). For both experiments, students are expected to process the information
Proceedings of Research in Engineering Education Symposium 2011
Madrid, 4 th - 7 th October 2011