ASQ Reliability Division October 10, 2019 Timothy M. Hicks, P.E. - - PowerPoint PPT Presentation

ASQ Reliability Division October 10, 2019

Timothy M. Hicks, P.E. (Mechanical Performance) Roch J. Shipley, Ph.D., PE, FASM (Materials)

 Structural integrity is ensured in the design phase by a thorough

review of a product’s intended use and foreseeable misuse

• Testing is performed for verification
• Materials of construction are reviewed
• Manufacturing process controls ensure that the design intent is met
• Documentation addresses operation, maintenance, and inspection, with

warnings

 The testing methods utilized for design verification and

validation are also critical when it comes to analyzing failures

 Today’s focus will be to:

• Discuss some different aspects of structural integrity testing
• Provide an overview of processes utilized to ensure a successful and safe

design

• Provide guidance to get it right the first time, avoiding any need for failure

analysis

 Timothy M. Hicks, PE (Tim)

• Mechanical Engineer

▪ BS - Michigan Technological University ▪ MS – Rensselaer Polytechnic Institute

• Industry – 36 years experience

▪ 27 years in design, testing, and manufacturing ▪ 9 years in engineering consulting

 Roch J. Shipley, PhD, PE, FASM

• Materials Engineer

▪ BS and PhD – Illinois Institute of Technology

• Industry – 39 years experience

▪ 10 years in manufacturing and corporate research ▪ 29 years in engineering consulting

 General overview

• Wide variety of companies and industries on call

 Please ask questions during or after presentation  Broad overview of topics  Don’t hesitate to seek out more information from

• colleagues
• suppliers
• industry groups
• technical societies
• additional experts
• follow-up with us afterwards (contact info at the end)

 Requirements  Design concept  Detailed design  Failure Mode Effects Analysis (FMEA)

• So issues are recognized and avoided to the fullest

extent possible

 Assess, test, and validate

• Software modelling
• Full scale prototypes
• Materials samples

 Goal is to be both efficient AND complete

 Design still in concept phase – Low  Manufacturing in progress – Medium  Products in distribution chain – High  Products in the field – Even higher  Failures have occurred in the field - Highest  Therefore, test early and often!

 Thousands of recalls per year  Recalls.Gov combines

• CPSC (Consumer Product Safety Commission)
• NHTSA

SA (National Highway Traffic Safety Admin)

 914 recalls of 29 million motor vehicles in 2018

• USCG (United States Coast Guard)
• EPA

EPA (Environmental Protection Agency)

• USDA (United States Department of Agriculture)
• FDA (Food and Drug Administration)

 Compilations on sites such as

• https://www.statista.com/topics/3798/product-recalls-

in-the-united-states/

• Again, test early and often!

 Dimensional  Appearance  Load → Stress

• Specification
• Reasonably foreseeable

 Usage / Wear  Maintenance, inspections, service

• Consequences of deviations

 Temperature

• Operation
• Shipment, storage, etc.
• Washing, sterilization (medical devices)

 Chemical

• Operation
• Biocompatibility
• Washing, including adjacent components, sterilization, etc.

 UV

• Natural
• Sterilization

 Radiation

• Sterilization
• Again, specified vs. reasonably foreseeable
• Nuclear – another whole area

 Metal  Plastic / Polymers  Ceramic  Composite material

• Concrete
• Wood

 Concepts apply to all materials, details differ

 Casting  Forging  Molding  Welding  Machining

• Surface finish
• Stress concentrators
• Might remove beneficial grain flow in formed parts
• Residual stress

 Heat treatment  Stamping  Additive (3D printing)

 Evaluates all possible failure modes for

manufacturing processes and product useage

 Critical dimensions, surface finish, etc.  Materials / components themselves do not

fail

• Respond to environment – predictable ways

(engineer’s responsibility)

 Load / stress – including complex stress states, residual stress  Chemical / Corrosion  Temperature  Wear

 Testing to address potential materials “failures”  Mechanical loads → stress

• Processing → may introduce residual stress

 Residual stress – heating – thermal expansion etc.  Shot peening (beneficial)

 Again, verify

• Deformation

 Elastic  Plastic (permanent)

• Buckling
• Fracture

 Chemical environment  Wear

 Temperature – high or low

• Thermal expansion and stress

 Varies with material

• Change in mechanical properties
• Change in lubricant performance
• Enable or accelerate chemical reactions

 E.g. Oxidation, changes in material

 TESTING ESTABLISHES

ABLISHES & QUANTI NTIFIES FIES

• Feasibility
• Product specifications

 TESTING VA

VALIDAT DATES ES

• Product concepts - prototypes
• Product specifications
• Product performance
• Manufacturing processes
• Aging/wear-out mechanisms
• Failure modes

 TESTING MONITORS

ITORS

• Manufacturing processes
• Product aging / wear
• Product performance

 Standard properties and test methods

• Publicly available
• Or company standards
• Clear communication all along the supply chain

 Not handbook and similar “typical” or average

properties.

 Not supplier typicals

• What happens when supplier changes?

 ASTM (American Society for Testing and

Materials) – 12,500+ documents

 ANSI (American National Standards Institute)

9,500+ documents

 SAE (Society for Automotive Engineers)

10,000+ documents

 IEEE (Institute of Electrical and Electronics

Engineers) – 1,100+ documents

 ISO (International Organization for

Standardization) – 22,600+ documents

 International Electrotechnical Commission

(IEC) – 9,000+ documents

 International Telecommunications Union (ITU)

4,000+ documents

 Chemical composition

• Plastics less standardized than metals
• Plasticizers, additives for UV exposure

 Mechanical properties  Heat treatment  Microstructural requirements  Non-destructive examination  Manufacturing processes

• Including personnel, e.g. welding certifications

 Surface finish, coatings, friction  Corrosion and wear resistance  At temperatures of interest  And more  Control with test program

 Materials  Test procedures

• Match functional requirements

 Accredited laboratory  Supplier certification with every order, if

feasible

• Protect yourself and your company
• Avoid misunderstandings
• Keep on file

 Component  Sub-system  System  Full product  Cyclic or peak load  Accelerated durability  Field performance  Dormant state shelf life (e.g. airbags, oxygen

system on aircraft, fire detection systems)

 Functional testing  Performance testing  Reliability testing  Environmental testing  Mechanical testing  Mean time between failures (MTBF) prediction

• Many product lives follow Weibull distribution
• Important for setting warranty terms

 Conformance testing  Safety certification

• Determine useful life and factor of safety

 Product Testing (Mechanical Lab/Field)

• Functional Testing
• Stress Testing
• Performance Testing
• Environmental Testing

 Materials Characterization (Analytical Lab)

• Analytical Chemistry
• Chemical composition and microstructure
• Microscopy
• Surface Analysis
• Mechanical Property Testing

 Finite Element Analysis/Modeling (FEA)  Experimental Stress Analysis

• Strain gages
• Various coatings

 Component Testing

• Prototype
• Early production

 System Testing

• Prototype
• Early production
• Audit

 Powerful tool to evaluate design

alternatives

 Inputs must match real world

 Material properties, grid size, boundary conditions, temperature, etc.

 Validate model with physical test to

• btain correlation

 Do the materials of construction

• Meet specification?
• Appropriate for the application?
• Behave as expected?

 Much can often be learned through

examination of failed test specimens

• Loads
• Temperature
• Chemical environment
• Weld process
• Contact/witness marks, wear, etc.
• Assembly

 Scientific Method – hypothesis testing

• Has anything changed?

 Many tests are destructive, so statistical

analysis is necessary

• Integrate with Statistical Process Control (SPC), etc.

 Yield

• Affected by temperature, strain rate

 Ultimate

• Affected by temperature

 In aggressive environment

• Stronger is not always better!

 Fatigue

• Affected by corrosion

From Instron, one supplier of testing machines

*

Force/Area Change / Original Length

 Location is part of specification  Separately manufactured test bars

• Castings, forgings, etc.
• Avoid misinterpretation – properties may vary

 Directionality may be important  Hardness correlated with tensile strength

• Considered non-destructive

 Goal – reproducible results – material

property

 Specimen geometries (proportional)  Test as received or after environmental

exposure

 Strain rate (applied force)  Stress rate (change in length)  Temperature

• ASTM E21 if elevated temperature

 Report as desired

• Engineering stress strain – based on initial

dimensions

• True stress strain –

 account for decreasing area  show strain hardening

 Ductile, micro void coalescence, dimpled

rupture

 Brittle

• Cleavage, transgranular
• Intergranular
• Can result from both material and environmental

conditions

 Ultimate stress – overload  Progressive (time dependent)

• Constant stress

 Stress corrosion cracking  Hydrogen embrittlement  Metal embrittlement  Creep, stress rupture

• Cyclic stress - fatigue

 Mean, alternating,  R.R. Moore – mean is 0, fully reversed

Environment surrounds the specimen

Reference: ASM Handbook of Failure Analysis and Prevention, (Volume 11), ASM International, 2002.

 Measure energy to fracture, e.g. Charpy  Applicable to metals and non-metals

• Steels exhibit ductile – brittle transition with temp.

 Test as received or after env. exposure

 Plane strain fracture toughness  A material property  Measure of material resistance to crack

propagation

 Used in damage tolerant design

• For highly stressed parts in which cracks are likely

to develop

• How often should the component be inspected so

that a crack will be detected before it grows to critical length

 Because materials and properties may vary

throughout a component

 State of stress may also vary  Full scale component/systems tests are often

performed

CETestGroup.Com

Ride de the e Duc ucks ks – Seattle attle Acc cciden ident 2015 015

• WWII vintage single use combat vehicles
• Vehicles stretched repurposed for tourism including front axles being

rebuilt but were not verified for application or repetitive loading / usage

• After initial front axle fractures during use, no analysis was performed
• Implemented repair that was insufficient and poorly executed, and

covered up ability to visually inspect for cracks

• Catastrophic front axle failure resulted in loss of vehicle control, causing

a head on collision, with multiple fatalities and injuries

Ride e the Ducks ks – Seattle ttle Accid ciden ent 2015 15 con’t:

Options available to avoid failure and accident:

• Design analysis at beginning would have shown the axles had an inherent

crack initiation point – groove cut to improve turning radius performance

• Materials and stress analysis for developing field repair
• Ultrasonic, magnaflux, or X-ray testing during inspections would have

detected cracking before fracture

“Trust but verify…”