Modelling of a Miniature punch diskModelling of a miniature punch disk
In the industries, accurate measurements of the mechanical and strength properties of the metals are very crucial for an
effective and well-rounded planning, design and manufacture of components from the metals (Lewis 1). Unfortunately however,
due to certain constraints such as material unavailability or limitedness, among other factors the tests cannot be
effectively carried out. According to CEN (2007) for instance, the full scale destructive testing of components will ensure
an accurate analysis of the component. However, this kind of testing will require that the material be completely discarded
as it has been rendered useless in service (because welding the components back will reduce efficiency and increased risk of
failure in service) (Matocha&Hurst 1).
As a result, modeling testing methods have been introduced to replace the destructive testing, while giving results nearly
similar as if the destructive tests have been carried out. Miniature disks are developed to confirm the certain mechanical
properties of the material being tested, using a very small quantity of the material. In addition, the tests are used in
rapid solidification technology, failure analysis, life cycle assessment, coatings, properties of weldments etc. (Karthik 1).
Miniaturization or better put, miniaturized specimen technology (MST) is a concept originated from the practices in the
nuclear industry. This is because of the delicate behavior of nuclear element, the insufficient and expensive neutron
irradiation space(Klevtsov et al. 101), nuclear test specimens were then miniaturized or made available in small quantity for
the testing facility (Karthik 1). (Klevtsov et al. 101) mentioned it is only feasible to use miniaturized test specimen a
number of future fusion reactor alloy development irradiations.
The miniaturization modeling is carried out in order to investigate and understand accurately and reliably, the mechanical
properties of metals and steel products. The modeling process requires that certain properties of the metal steel, say the
tensile strength, is carried out and compared with the previous works on miniature testing and with simulated designs carried
out using the finite element analysis (FEA) (Lewis 1). The result from this comparison gives an indication of the
performance of the component so produced (or to be produced) in service.
Theoretically, the punch test’s major mode of deformation is shear happening between the clearance zone of the test specimen
and the lower die surface (Klevtsov et al. 101). Generally, it is a blanket operation (Karthik 2). When spherical indenters
are used, the geometry of indentation differs from nonspherical indenters. For the former, with increase in penetration, the
geometry of indentation changes, thus making it very suitable for determining a complete stress-strain curve of miniaturized
metals (Karthik 2). In Modelling of a miniature punch disk, the following process is captured. A flat end cylindrical punch
is used to punch a hole in a disc specimen clamped and secured in position. From the set-up, a plot of load displacement is
obtained (Karthik 1) similar to the conventional tensile test plot.
The modelling methodology will capture the plasticity models with a nonlinear modelling in which total strain = elastic
strain + plastic strain. The model will adopt a linear isotropic elastic behavior as the elastic criterion in which the
modulus of elasticity and shear stress gives bulk moduli and shear. A flow rule to determine the increment in plastic strain
from that in load. A hardening rule that guides the yield criterion during plastic deformation is also captured.
Disk-shaped specimens to be modelled will nominally be 3.0 by 0.25mm, using a nonstandard loading configuration due to their
small size (Klevtsov et al. 101). The mechanical property test of this disk is achieved by pushing a rod of a pre-determined
radius through the disk until it punches it to failure. The response of this loaded disk to the force applied by the rod is
graphically produced in the form of a force – displacement curve by the computer. Finite element analysis will be performed
in converting load/deformation results from the experiment to more useful stress/strain results (Partheepan et al., 1).
The horizon computer software was connected to the tensile machine setup to record the deformations. The software serves as
the input model for the machine, where in parameters from thickness of disc, diameter of disc and speed of crosshead were
inserted. The test was then started and stopped only when the sample is damaged. The process was repeated for then other
samples, each time, the result of the load and displacement was fed back in to Horizon software which records in excel
spreadsheet. All tests were carried out in accordance with procedures outlined in the “European code of practice for small
punch test method for metallic materials”.
The test was repeated nine more times in order to obtain ten different results so that an acceptable level of consistency is
achieved and the average taken. After the test, the results were all collated in excel. The results are used to validate the
model against experimental results. The comparison showed both the test samples and simulation showed the same method of
failure while the stress recorded was greatest when the disc failure was becoming obvious. This is the whole essence of
modeling; to compare the simulated result against the experimental results
In conclusion, the miniature punch disk testing method can be considered to be an accurate method of investigating the
mechanical property of metals. It is a convenient modelling testing method that can substitute the commonly used destructive
testing in which materials are lost.