Impact hammer test of an Aluminium 6082 T6 plate, 260 x 246 x 1.5 mm, free boundary conditions

Plate data

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E = 70 GPa

ν = 0.33

ρ = 2700 kg/m^3

h = 1.50 mm (±0.01mm)

width = 246 mm

length =  260 mm

Experiment description

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- a Cartesian coordinate system (XYZ) is defined in one of the corners of the plate, with XY laying on the mid-plane of the plate;

- the X axis is aligned with the length direction;

- the Y axis is aligned with the width direction;

- the free boundary conditions are approximated experimentally by means of soft cotton wires, and the plate is tested while hanging on the cotton wires that are fixed at two corners, by means of adhesive tapes;

- a mesh of 5 by 5 points is defined on the plate, with the following coordinates (in meters):

1, [0., 0.]
2, [0.065, 0.]
3, [0.13, 0.]
4, [0.195, 0.]
5, [0.26, 0.]
6, [0., 0.0615]
7, [0.065, 0.0615]
8, [0.13, 0.0615]
9, [0.195, 0.0615]
10, [0.26, 0.0615]
11, [0., 0.123]
12, [0.065, 0.123]
13, [0.13, 0.123]
14, [0.195, 0.123]
15, [0.26, 0.123]
16, [0., 0.1845]
17, [0.065, 0.1845]
18, [0.13, 0.1845]
19, [0.195, 0.1845]
20, [0.26, 0.1845]
21, [0., 0.246]
22, [0.065, 0.246]
23, [0.13, 0.246]
24, [0.195, 0.246]
25, [0.26, 0.246]

- the accelerometer is fixed at point 5;

- the time-response to the hammer impact is obtained for each point by hitting with the impact hammer at each point;

- three time-response data points are obtained at each point;

- for all measurements a total of 2^15 = 32768 time samples are obtained, corresponding to a time interval of 0 <= t <= 3.840 s, and a minimum sampling rate of 8000 Hz.  

Details about the hardware

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1) Data Acquisition Module NI 9234

With four input channels simultaneously acquire at rates up to 51.2 kS/s (kilosamples per second). The operating temperature limits are from -40 °C to 70 °C, maximum of 5 g vibration, and maximum of 50 g shock.

2) Impact hammer with load cell 086C02

The first channel corresponds to the impact hammer load cell measurements, in Newtons [N]. The hardware sensitivity (+-15%) is 50 mV/lbf or 11.2 mV/N.

3) Unidirectional Accelerometer 352A24

The second channel corresponds to the accelerometer measurements, in gravity units [g], being 1 gravity unit = 9.81 m/s^2. The hardware sensitivity (+-10%) is 100 mV/g or 10.2 mV/(m/s^2).

Reading the experimental data

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I use the https://nptdms.readthedocs.io/en/stable/quickstart.html module to read the experimental data saved with the "*tdms" extension. The following example illustrates how to read the data at all the points:

from nptdms import TdmsFile

# reading from the experimental results
# - the hammer impact force in [N] as a function of time from df.iloc[:, 0]
# - the accelerations in [g] as a function of time from df.iloc[:, 1]
times = {}
hammer_impacts = {}
accelerometer = {}
for point in usedpoints:
    tdms = TdmsFile('WaveForms Point%02d.tdms' % point)
    df = tdms.as_dataframe()
    df.index = df.index/df.shape[0] * tmax
    times[point] = df.index
    hammer_impacts[point] = df.iloc[:, 0] 
    accelerometer[point] = df.iloc[:, 1]