07/03/2017. Now, XJTU is a comprehensive university with 17 Academic Schools and 4 Teaching Hospitals. Xi an

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1 西安交通大学航天航空学院 School of Aerospace, Xi an Jiaotong University Advanced Electromagnetic Nondestructive Testing and Evaluation (NDT&E) Yong Li 3/7/2017 ENDE Mother city: Xi an Xi an 3/7/ Xi an Jiaotong University (XJTU) XJTU was founded in 1896 as Nanyang College in Shanghai, officially renamed as Jiaotong University in 1921, and was one of the earliest institutions of higher learning in China. Now, XJTU is a comprehensive university with 17 Academic Schools and 4 Teaching Hospitals. Energy and Power Engineering---No.1 in China Management Science ---No.1 in China Business Administration---No.1 in China Electrical Engineering---No.2 in China Mechanical Engineering---No.3 in China 3/7/

2 NDT&E Lab of XJTU Founded: 2005 Staff: 1 Prof., 3 Associate Prof. Students: 12 Ph.D Candidates, 21 Master Students Research Topics: NDT&E, Electromagneto Mechanical Coupling Budget: National Projects, Budgets from University and industry 3/7/ WHO AM I? --- A guy in ENDT&E Name: Yong Li Position: Associate Professor, Xi an Jiaotong University (XJTU) Education: BS B.Sc (2001, XJTU) M.Sc (2004, XJTU) Ph.D (2009, NCL) Work experience: Research Assistant ( ) 2009) Research Associate ( ) 2010) 3/7/ Contents Eddy current-based techniques: Eddy current Testing Alternating Current Field Measurement Pulsed Eddy Current Testing Magnetism-based technique: Magnetic Flux Leakage EM-Wave-based Technique: Electromagnetic Acoustic Transduction Principle and physical phenomena Typical signals Information extracted from signals Simulations THEORY 3/7/

3 What is NDT? Nondestructive testing (NDT) are noninvasive techniques to determine the integrity of a material, component or structure or quantitatively measure some characteristic of an object. ---from NDT Wiki 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. In other words, when the inspection or test is completed the part can still be used. ---from ASNT 3/7/ Key points (NDT vs. Medical Science) No damage to structures No influence on application Evaluation of defects Structural Integrity assessment Testing and evaluation of material properties No harm to human body No side effect Illness analysis Health evaluation Blood test, heart-beat, body temperature, pulse on wrist 3/7/ Development (I T E) Nondestructive Inspection (Damage?) Nondestructive Testing (Location of defects?) Nondestructive Evaluation (More quantitative in nature, defect size/shape/orientation, material properties) 3/7/

4 What is ENDT? techniques which use the induction of an electric current or magnetic field into a conductive part, then the resulting effects are recorded and evaluated from ASNT the process of inducing electric currents or magnetic fields or both inside a test object and observing the electromagnetic response from NDT Wiki Techniques based on Electromagnetism (physical phenomena, EM field response to defects, testing/resulting signals, instrumentation, etc.) 3/7/ Electromagnetism Electromagnetism is a branch of physics involving the study of the electromagnetic force, a type of physical interaction that occurs between electrically charged particles. The electromagnetic force usually exhibits electromagnetic fields such as electric fields, magnetic fields, and light and is one of the four fundamental interactions (commonly called forces) in nature. 3/7/ Electromagnetic field An electromagnetic field is a physical field produced by electrically charged objects. It affects the behaviour of charged objects in the vicinity of the field. The electromagnetic field extends indefinitely throughout space and describes the electromagnetic interaction. Electromagnetic ti field = Electric field + Magnetic field Stationary charges or time-varying magnetic field Moving charges 3/7/

5 Electric field In physics, the space surrounding an electric charge or in the presence of a time-varying magnetic field has a property called an electric field. This electric field exerts a force on other electrically charged objects. 3/7/ E-field vs. E-field (Electrostatics) Electrostatic fields are E-fields which do not change with time, which happens when charges and currents are stationary. In that case, Coulomb's law fully describes the field. 3/7/ E-field vs. M-field (Electrodynamics) Electrodynamic fields are E-fields which do change with time, for instance when charges are in motion. The electric field cannot be described independently of the magnetic field in that case. A magnetic field changing in time produces a curled electric field, possibly also changing in time. The situation in which electric or magnetic fields change in time is no longer electrostatics, but rather electrodynamics or electromagnetics. 3/7/

6 Faraday's law of induction Faraday's law of induction is a basic law of electromagnetism predicting how a magnetic field will interact with an electric circuit to produce an electromotive force (EMF) a phenomenon called electromagnetic induction. 3/7/ Faraday's law of induction The induced electromotive force in any closed circuit is equal to the negative of the time rate of change of the magnetic flux enclosed by the circuit. Electromotive force is the voltage developed by any source of electrical energy such as a battery or dynamo. It is generally defined as: electrical potential for a source in a circuit. around a closed loop the electromagnetic work that would be done on a charge if it travels once around that loop. 3/7/ Magnetic field Magnetic fields can be produced by moving electric charges and the intrinsic magnetic moments of elementary particles associated with a fundamental quantum property, their spin. Magnetic field sources are essentially dipolar in nature, having a north and south magnetic pole. 3/7/

7 Magnetic field vs. Electric field All moving charged particles produce magnetic fields. Moving point charges, such as electrons, produce complicated but well known magnetic fields that depend on the charge, velocity, and acceleration of the particles. 3/7/ Magnetic field vs. Magnetic field Lenz s Law: The direction of current induced in a conductor by a changing magnetic field due to Faraday's law of induction will be such that it will create a field that opposes the change that produced it. 3/7/ Ohm s Law The current through a conductor between two points is directly proportional to the voltage across the two points. 3/7/

8 Eddy current technique (EC) Applications: Crack detection Material thickness measurements Coating thickness measurements Conductivity measurements for: Material identification Heat damage detection Case depth determination Heat treatment monitoring Eddy current inspection is one of several methods that use the principal of ELECTROMAGNETISM as the basis for conducting examinations. Several other methods such as Remote Field Testing (RFT), Flux Leakage and Barkhausen Noise also use this principle. ---NDT Wiki 3/7/ Principles of EC Excitation coil Primary magnetic field Eddy currents Secondary magnetic field Conductive specimen 3/7/ Principles of EC 3/7/

9 Skin effect and penetration depth Eddy currents concentrate near the surface adjacent to an excitation coil and their strength decreases with distance from the coil. Eddy current density decreases exponentially with depth. This phenomenon is known as the skin effect. ( ed.org) 3/7/ Eddy Currents 3/7/ Inductance When induction occurs in an electrical circuit and affects the flow of electricity it is called inductance, L. Self-inductance: the property of a circuit whereby a change in current causes a change in voltage in the same circuit Mutual inductance: one circuit induces current flow in a second nearby circuit 3/7/

10 Inductance - 3/7/ Self inductance 3/7/ Self inductance 3/7/

11 Self inductance, inductive reactance 3/7/ Mutual inductance 3/7/ Mutual inductance 3/7/

12 EC and electric transformer 3/7/ Impedance 3/7/ Impedance plane REAL=(R-R 0 )/X 0 IMAG=X/X 0 3/7/

13 Testing principle 3/7/ Factors related to system performance Conductivity Permeability Excitation Frequency (50Hz-10MHz) Sensitivity Detection depth Spatial resolution Coil size Lift-off 3/7/ Simulations 3/7/

14 Simulations (TEDDY) 3/7/ Thank you! and Any Questions? Yong Li Tel: +86 (0) Web: 3/7/