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 (National Highway Traffic Safety Admin) 914 recalls of 29 million motor vehicles in 2018

◦ USCG (United States Coast Guard)

◦ 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 & QUANTIFIES◦ Feasibility◦ Product specifications

TESTING VALIDATES◦ Product concepts - prototypes◦ Product specifications◦ Product performance◦ Manufacturing processes◦ Aging/wear-out mechanisms◦ Failure modes

TESTING MONITORS◦ 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 obtain 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 the Ducks – Seattle Accident 2015- 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 the Ducks – Seattle Accident 2015 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…”