Employment Of Ultrasonic Flaw Detection In Testing

Abstract

Technology has become an integral part of life due to which there are new innovation and job created daily. This technology has changed the way we live it has bought improvement in everything around us, that also includes the field of travel also, because the need for men and material has increased in the recent years. The transport plays a major role in the functionality of industries, because it provides raw material and it helps in transport of the finished goods after production also.

One of such major transport modes is railways, it helps in speedy and mass transportation of both men and materials for the industries. But due to the daily usage and poor maintenance of railways track, it may lead to formation crack or breakage which will stand as a barrier for safety.

As the railways network present in a nation is very large, manual inspection of each and every track is impossible. So, varies method are present for inspection of the railways track which includes both destructive and non- destructive techniques.

As the destructive technique needs collection of samples mostly Non-Destructive Techniques (NDT) methods are used. One of such method is ultrasonic testing method which helps in testing of railway track without any loss. In this method high frequency sound used for diagnosing of track which gives a highly précised value. For the reduction of time and human effort, this method is combined with live robot for the purpose of automatic inspection. This helps in development of the solution for any problem that is been encountered.

Introduction

The Indian Railways has one of the largest railway networks in the world, crises-crossing over 1, 15,000 Km in distance all over India. However, with regard to safety Indian Railways are not up to the global standards. According to recent survey 25% of track length is in need of replacement due to the development of cracks on it. Manual detection of cracks not fully effective owing to much time consumption and requirement of skilled technicians. Nondestructive testing (NDT) is the process of inspecting, testing, or evaluating materials, components or assemblies for discontinuities, or differences in characteristics without destroying the serviceability of the part or system.

Other tests are destructive in nature and are therefore done on a limited number of samples, rather than on the materials, components or assemblies actually being put into service. But discontinuities and differences in material characteristics are more effectively found by NDT.

NDT Test Methods Overview

The types of test methods are varying with the type of penetrating medium and or the equipment used to perform that test. The current NDT methods are:

• Acoustic Emission Testing (AE)
• Electromagnetic Testing (ET)
• Guided wave testing (GE)
• Ground penetrating Radar (GPR)
• Laser Testing Methods (LM)
• Leak testing (LT)
• Magnetic Flux Leakage (MFL)
• Microwave Testing, Liquid Penetrant Testing (PT)
• Magnetic Particle Testing (MT)
• Neuron Radiographic Testing (NR)
• Infrared Testing (IR)
• Ultrasonic Testing (UT)
• Vibration Analysis (VA)
• Visual Testing (VT)

Among those test methods, the six most frequently used test methods are MT, PT, RT, UT, ET and VT. In this project we used Ultrasonic method for Railway inspection.

Ultrasonic Testing Methodology

Ultrasonic Testing (UT) uses high frequency sound energy to conduct examinations and make measurements used for flaw detection or evaluation, dimensional measurements, material characterization, etc., A typical UT inspection consists of pulsar/receiver, transducer, and display devices. A pulsar/receiver is an electronic device that can produce high voltage electrical pulse. Driven by the pulsar, the transducer generates high frequency ultrasonic energy.

The sound energy is introduced and propagates through the materials in the form of waves. When there is a discontinuity (such as crack) in the wave path, part of energy will be reflected back from the flaw surface. The reflected wave signal is transformed into electrical signal by the transducer and is displayed on a screen. In the applet below, the reflected signal strength is displayed versus the time from signal generation to when an echo was received. From the signal, information about the reflector location, size, orientation and other features can sometimes be gained.

Advantages of Ultrasonic Testing:

• It is sensitive to both surface and subsurface discontinuities.
• The depth of penetration for flaw detection or measurement is superior to other NDT methods.
• It is high accuracy in determining reflector position and estimating size and shape.
• Electronic equipment provide instantaneous results.
• Minimal part preparation required.
• Detailed images can be produced with automated systems

Limitations:

• Surface must be accessible to transmit ultrasound.
• Skill and training are more extensive than with some other methods.
• Materials that are rough, irregular shape, very small, exceptionally thin or not homogeneous are difficult to inspect.

Components Descriptions

• NDT Testing Machine. ‘The Ultrasonic Flaw Detector’ is the machine used for Non-Destructive Testing of a wide range of components.
• Testing Probe. The probe is the device used to detect the crack in the railway rails. It is a transducer which is contact to the railway track to detect the crack. The type of transducer used in this system is a contact transducer.
• Vehicular Robot. An automatic robot vehicle is a autonomous vehicle which can perform the desired function without human intervention. It can also provide accurate results and maintain high degree of accuracy over a long period of time. The term Robotic vehicle used because this vehicle combined both the function of a Robot and conventional vehicle. We have implemented a robotic mechanism on a vehicle in order to detect the crack in the railway rails.
• Arduino Mega. The Arduino Mega 2560 is a microcontroller board based on the ATmega2560. It has 54 digital input/output pins (of which 14 can be used as PWM outputs),16 analog inputs, 4 UARTs (hardware serial ports), a 16 MHz crystal oscillator, a USB connection, a power jack, an ICSP header, and a reset button. It contains everything needed to support the microcontroller; simply connect it to a computer with a USB cable or power it with a AC-to-DC adapter or battery to get started. The Mega is compatible with most shields designed for the Arduino Duemilanove or Diecimila.
• Battery. The battery is an energy device which gives the power supply to the motors and other electrical components to do their functions. The type of battery used in this application is rechargeable battery with the capacity of 12v and 2A.

Design and Analysis

• Isometric Views. We have a 3-D rendering of our robot created using Creo 2.0. It explains the basic layout of our robot on the railway track. The structure is divided into two parts – The Upper portion housing the Ultrasonic Machine and Wheels, and the Lower portion housing the XY Linear Mechanism. The two sections can be detached from each other and carried separately thus allowing dismantling of our robot with ease.
• Analysis of Chassis. The chassis is then subject to displacement analysis using ANSYS software for thorough evaluation of its structural capabilities. The following analysis confirms that the chassis is able to withstand upwards of 15kg of load acting on it while allowing free lateral movement of the wheels.

Design Calculations

Calculation Of Design Torque:

𝑇 = 𝐹 ∗ 𝑅

Where T refers to Torque,

F refers to Force,

Force = Mass ∗ Accelaration due to gravity

𝐹 = 10 ∗ 9.81 = 98.1𝑁

R refers to Radius 0.0375m,

Torque = 98.1 × 0.0375

Torque= 3.67 N-m.

Power Calculation of the Motor:

𝑃 = 𝑉 ∗ 𝐼

Where ‘P’ refers to Power,

‘V’ refers to Voltage, ‘I’ refers to Current.

Here we have used Battery with 12Volts, 3Ampere.

𝑃𝑜𝑤𝑒𝑟 = 12 ∗ 3 = 36𝑊𝑎𝑡𝑡𝑠

Speed Calculation of a Motor:

𝑃 =

2𝜋𝑁𝑇

60

Where P refers to Power W,

T refers to Torque N-m,

N refers to speed of the Motor.

N= 60∗𝑃

2𝜋𝑇

= 36∗60

2𝜋∗1.839

Speed N = 93.7 rpm.

Drive Wheel Motor Torque Calculations

During the selection of motors which is capable of producing enough torque to drive the robot, it is always necessary to calculate the force applied between the tire and inclined surface to move a robot.

Total Tractive Effort, 𝑇𝐸 = Force necessary to overcome rolling resistance + Force necessary move a vehicle upon a slope + Force necessary to accelerate to final maximum speed in desired time.

Gross vehicle weight, 𝑅𝐺 : 10 kg(98.1 N)

Weight on each drive wheel : 24.5 N

Radius of wheel/tire 𝑅𝐷 : 0.0375m (37.5 mm)

Preferred top speed 𝑆𝑀 : 0.1 m/s

Preferred acceleration time : 5S

Maximum incline angle, α : 20

Working surface : Dirty/sandy

Determination of force necessary to overcome rolling resistance:

Rolling resistance is the force necessary to drive a vehicle over a particular surface.

Rolling Resistance (RR) = gross vehicle weight × surface friction

= 98.1 × 0.037

RR = 3.62 N

Determination of force necessary to move a vehicle upon a slope:

Grade resistance is the amount of force necessary to move a vehicle up a slope.

Grade resistance (GR) = gross vehicle weight × sin α

= 98.1 × sin 20

GR = 3.423 N

Force to accelerate to final maximum speed in preferred time:

Acceleration force is the force necessary to accelerate from a stop to maximum speed in a desired time.Acceleration force

(AF) = (gross vehicle weight × preferred maximum speed) /

(9.815 × time required to achieve a maximum speed )

98⋅1∗0⋅1

98.1∗5

= 0.2𝑁

AF = 0.2 N

The total tractive effort is the sum of the force necessary to overcome rolling resistance, force necessary to move a vehicle upon a slope and force necessary to accelerate to final maximum speed in preferred time.

Total Tractive Effort (TE) = 3.62 + 3.423 + 0.2 = 7.243N

TE = 7.243 N

Determination of Wheel Motor Torque

To verify the vehicle will perform as designed in regards to tractive effort and acceleration , it is necessary to calculate the required wheel torque based on the tractive effort.

Wheel Torque, TR (N-m) = Total tractive effort × Radius of

Wheel × Resistance Factor

The resistance factor accounts for frictional losses between the wheels and their axles and the drag on the motor bearings.

Typical value range between 1.1 and 1.15.

TR = 7.243 × 0.0375 × 1.1

TR = 0.298 N-m.

Reality validation of Motor wheel torque:

To verify that the vehicle can transmit the required force from the drive wheel to the ground, the maximum tractive torque a wheel can transmit is equal to the normal load times the friction coefficient between the wheel and the ground times the radius of the drive wheel.

The maximum tractive torque = weight on the drive wheel*µ*

Radius of drive Wheel/tire (m)

= 24.5 ∗ 0.45 ∗ 0.0375

𝐓𝐦𝐚𝐱 = 0.413 N-33388m.

Since the total wheel torque calculated is less than the sum of the Maximum Tractive Torques for all drive wheels the slipping will not occur.

Result

Ultrasonic test methods provide quantitative information regarding thickness of the component, depth of an indicated discontinuity, size of discontinuity etc. The output data is viewed by means of small web camera which is collected and the defects are identified by means of image processing system. It involves comparison of predefined data with acquired data and results are accomplished. When a machine detects the crack or a discontinuity in the railway track the high peak was shown in the machine that informs the detection of a crack. Due to the sensibility of the Ultrasonic testing even a minute crack in the inside of the track can be selected.

Conclusion

This project is made with pre-planning, that it provides flexibility in operation. This innovation has made the more desirable and economical. This project “Employment Of Ultrasonic Flaw Detection In Testing Of Railway Cracks” is designed with the hope that it is very much economical and help full to the Indian Railways and Public Safety. By using this automated control robot, testing can be done on both the top and sides of the railway tracks and also human work is reduced. Along with that ultrasonic testing method increases the accuracy of crack detection and results are viewed and stored by means of image processing system. The robot can also be programmed for different length of the tracks and testing can be done and the cracks are predicted in an easier way.