Abstract
This experiment explores damping and the effects of different testing parameters. In this laboratory exercise, data on how various damping treatments and the impact of imperfect boundary conditions affect the measure parameters. In particular, the half-power bandwidth technique and FRFs of an I-beam section were used to measure the modal damping of multiple modes in the frequency domain. This experiment also examined how various hammer tips changed the effective bandwidth of the measurement. The experiment was conducted in three parts, where part I used the cantilever beam, part II used the I-beam section, and part III used the I-beam section on a different platform. The data obtained from the experiments were collected and analyzed within the same part of the experiment. Based on the scrutinized data, the experiment concluded that the test parameters affected the damping ratio of I-beam.
Relevance
Some engineering fields rely heavily on damping data; hence, this experiment provides a way to understand this profession’s critical aspect. As such, engineers have to test different aspects of the materials used and their behavior when they are subjected to different forces. This experiment tests how I-beam behaves in different conditions, making it easy for engineers to understand how to use any particular material. The knowledge of material behavior with respect to forces and when other materials are added, for instance, foam, affected the I-beam’s behavior. The data collection skill gained in this experiment is relevant when real materials are tested for industrial purposes. Moreover, by comparing results from a different situation, one can notice how the material reacts, and this know give a rationale for the change.
Introduction
This project aims to learn how different situations affect the behavior of the cantilever beam and I-beam. The test is also essential in enhancing the skills that are relevant in the industry. This experiment was divided into three sections; the first used an aluminum cantilever beam that was clamped and its length measured. The second part of the test involved placing an I-beam on a form and attaching an accelerometer near one of its top flanges ends using wax. The accelerometer was then connected to NI DAQ Channel 1. The third part of the experiment involved returning the I-beam to the form and using a white nylon tip, and recording and exporting the top-flange-to-top-flange FRF with a range of 100Hz to 25 kHz.
Experimental Setup and Procedure
Equipment
- LabVIEW operating system
- Accelerometer
- Computer (Brand: DELL)
- BNC Cables
- Impact Hammer
- Cantilever Beam
- I-Beam
- Caliper and Rule
- White, Black, and Red Nylon.
Procedure
- The aluminum beam was secured in the clamp and its free length recorded. The fee length determined was used throughout this experiment. The gaps between the base of the clamp and the top at the four corners were set to correspond to the thickness of the beam, which was 1/16″. The accelerometer was attached to the beam’s tip using wax, and then it was connected to NI DAQ Channel 1. After the connection, LabVIEW was started, and SigFA_DomTF.vi loaded.
- The beam was given an initial displacement while keeping its tip displacement less than 10 percent of its length. Free decay was recorded and time series exported. The displacement was doubled for every subsequent test, and data recorded.
- Two of the clamp crews were loosened, and the other two were tightened, making the clamp crooked. This made the gaps between the clamp’s base and its top near 0″ on one side and about 1/8″ on its other side. The gaps were recorded, then free decay was recorded, and two free decay time series were exported using an initial displacement while keeping its tip displacement less than 10 percent of its length. The clamp was loosened then the beam was sandwiched between two rubber pads. The rubber/beam/rubber combination were properly clamped, and two more free decay time series exported using the same initial displacement.
- The clamped beam was restored by removing the rubber pad sandwiches. A tap-based damping treatment was applied on the surface of the clamped beam, and two free decay time series recorded and exported using the same beam free length and the initial displacement.
- An I-beam was placed on a form and accelerometer attached near an end of the top flange with wax’s help, and the system was connected to NI DAQ Channel 1. The impact hammer was connected to NI DAQ Channel 0. LabVIEW was started, and SigFA_DomTF.vi loaded. Data was exported up to 25 kHz, which dictated that a shorter length was used to limit the number of points of collecting data.
- A location on the top flange towards the end opposite the attached accelerometer was marked. A stainless steel hammer tip was used to record FRF from the marked point to the accelerometer. The recorded phase of FRF magnitude was exported from 100Hz to 25 kHz. Then apart at the bottom of the flange was marked and the corresponding FRF magnitude and phase exported from 100Hz to 25 kHz. A location on the bottom flange was marked, and the related FRF magnitude and phase, from 100 Hz to 25 kHz.
- The I-beam section was moved to the tabletop and FRF magnitude and phase exported from 100Hz to 25 kHz.
- The I-beam section was returned to the foam, and a white nylon tip was used to record and export the top-flange-to-top-flange FRF from 100Hz to 25 kHz. This part of the experiment was repeated for black and red rubber tips.