PDT 351 – Material Failure Analysis

PDT 351 – Material Failure Analysis

Failure in Service Very often, failure occurs to an industrial component during its service Failure is instability of a component to assume its intended function Major cause of failure include Improper design, e.g. material selection, load estimation Improper processing (fabrication) Improper use during the service, i.e. abuse of component © Wan Mohd Faizal

Example of failure Aircraft Accident : Aloha flight 243 in 1988
(miraculously only 1 victim) At that time, the aircraft experience 89,090 take off-landing cycle, well beyond design lifetime (75,000 cycles) At 24,000 ft altitude, the upper part of the fuselage rupture Spectacularly, the pilot manage to land safely the airplane Investigation suggested that the main cause of failure was fatigue crack propagation accelerated by corrosion. © Wan Mohd Faizal

Example of failure The sinking of the unsinkable Titanic, April 1912
(1517 victim) The hull of the Titanic was made up of steel having TDBT ≈ 30oc During the voyage to New York, Titanic collided with an iceberg The sea temperature was -2oc, way below TDBT The hull was highly brittle during the collision © Wan Mohd Faizal

Example of failure The collapse of Tacoma Narrows Bridge, 1940
A 1.8 km-long suspension bridge in Washington state, the first to used plate girder (I profile beam) to support the roadbed The main span collapsed under 64 km/hr wind 4 month after public opening Investigation suggested that the main cause of failure was aeroelastic flutter i.e. aerodynamic force on an object couple with a structure’s natural mode of vibration to produce rapid periodic motion © Wan Mohd Faizal

Type of failure Type of failure commonly uncounted
Yielding : permanent deformation Buckling : excessive elastic deformation Fracture : component separation Fatigue : failure due to repeated loading Creep : deformation that accumulates with time Corrosion : loss of material due to chemical action Wear : surface removal due to abrasion or contact © Wan Mohd Faizal

Design Approach © Wan Mohd Faizal

Why learning Design Against Failure ?
Avoid failure Provide general guidelines during the design, manufacturing, maintenance and use of engineering components Analyze failures Investigate the possible root cause of failure in an engineering component during the service Provided recommendations so that similar failure can be prevented in the future. © Wan Mohd Faizal

Report - Data Collection and Analysis

Data Collection and Analysis
. Analysis to determine the failure Macroscopic Analysis Non-destructing testing (NDT) Chemical Analysis Metallographic Analysis Mechanical Testing © Wan Mohd Faizal

. Analysis to determine the failure Macroscopic Analysis © Wan Mohd Faizal

. © Wan Mohd Faizal

Non-Destructing testing (NDT)
Method of Testing Capabilities Radiography Measures differences in radiation absorption Inclusion, Porosity, crack Ultrasonic Uses high frequency sonar to find surface and subsurface defects Inclusions, porosity, thickness of material, position of defect Dye Penetrate Uses a die to penetrate open defects Surface cracks and porosity Magnetic Particle Uses a magnetic field and ion powder to locate surface and near the surface crack Surface crack and defects Eddy current Based on the magnetic induction Measure conductivity, magnetic permeability, physical dimension, crack, porosity, and inclusions . © Wan Mohd Faizal

Engineering Report . © Wan Mohd Faizal

Course Outcomes (CO) At the end of the course, students should be able to… Describe, explain reliability engineering-defination on FMEA. Able to calculate reliability of simple engineering systems © Wan Mohd Faizal

What is FMEA? An industrial-strength Risk Assessment tool.
A set of systemized group activities intended to: Identify potential “failure modes” of a product or process Evaluate the “effects” of each failure mode on the system Define and prioritize action items to reduced the chance of failure mode to occurrence break the links between failure modes and effects Track the progress of all action items Document the entire process © Wan Mohd Faizal

Types of FMEA Design Process © Wan Mohd Faizal

Process FMEA Identifying the way in which a process can fail to meet critical customers requirements Estimating the risk of specific causes with regard to these failures Evaluating the current plan for preventing these failures from occurring Prioritizing the actions that should be taken to improve the process © Wan Mohd Faizal

When Are FMEAs Done? When a new process or service is to be implemented When a process is revised When there are a enough reported negative incidents for a given process to suggest that the process needs to be reviewed © Wan Mohd Faizal

FMEA Concepts Failure Mode - The ways in which a process can fail.
Potential Effect - Each failure mode has a potential effect, some effects are more likely to occur than others. Risk of Failure - Each potential effect has a relative risk associated with it. © Wan Mohd Faizal

FMEA Concepts RPN = S x O x D
a. S = Severity of the effect, given that the failure occurs b. O = Occurrence, probability of the failure mode c. D = Detection likelihood of the failure or effect not being detected before it is released for production Risk Priority Number – The value assigned to the severity, occurrence and detection of each potential failure on scale of 1-10 (low-high). RPN = S x O x D © Wan Mohd Faizal

Steps in FMEA Construct a detailed flow chart of the process.
Determine how each step could possibly “fail”. Determine the “effects” of each possible “failure”. Assign a Severity Rating for each effect. Determine the “cause” of each possible “failure”. Assign a Occurrence Rating for each effect © Wan Mohd Faizal

Steps in FMEA Assign a Detection Rating for each effect
Calculate and prioritize a Risk Priority Number (RPN) for each failure Review the process Take action to eliminate or reduce the Risk Priority Number Recalculate the resulting RPN as the failure modes are reduced or eliminated. © Wan Mohd Faizal

The FMEA Form (first half)
© Wan Mohd Faizal

The FMEA Form (second half)
© Wan Mohd Faizal

Concept of Stress and Strain

Concept of Strain . © Wan Mohd Faizal

Engineering Strain Tensor

Displacement Strain Relation

Principal Strains – Principal Direction of Strain

Principle Stress – Principal Direction of Stress

Deviatoric and Hydrostatic Part of a Stress Tensor

Equilibrium Equations

Hooke’s Law : Linear Elastic Material

Stress-Strain Relation

PDT 351 – Material Failure Analysis

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