Next Steps After Testing

Back to: Making Sense of Test Data

In a previous lesson, we considered the following questions when defining pass/fail criteria:

• What does the test mean if the parts pass?
• What does the test mean if one or more parts fail?

Depending on the results, there are several post-analysis actions an engineer can take after testing. If the test passes the test requirements, the design can be approved for production; however, there is typically more action taken post-analysis, even if the result is a true pass.

Validating the Result

If a test result is a true pass, the validity of the result must be confirmed. Devices under test (DUT) have inherent variability, meaning their materials, manufacturing processes, dimensional stack-ups, etc. are not perfectly controlled. Therefore, testing just one DUT is generally not acceptable. Engineers typically rely on statistical confirmation, hence the need for a sampling plan and/or Weibull analysis.

If a DUT fails under test, the engineer must determine the root cause of the failure, confirm the test parameters and setup, and then adjust the design (ideally) or the test before repeating. By using valid processes and reliable systems, engineers can confidently determine that the test itself is not an issue and, instead, a design flaw needs addressing.

Verifying several other test factors can help confirm the validity of the test result:

• • All sensors and equipment were properly calibrated
  • Consistent environmental conditions (e.g., temperature, humidity) were maintained
  • Test setup, procedures, and data recording processes were accurate and complete
  • Data analysis software was accurate (can be confirmed by comparing outputs with known inputs)
  • Test methods and results complied with industry standards and regulations

The engineer must also confirm that the DUTs were built to specification by checking the four Ms: man, method, material, and machine.

Improving the Design

Iterative testing is a product development test method in the product development cycle that runs repeated tests following incremental changes. Iterative testing can be used for design validation but also for design improvements.

Even with a true pass, an engineer might consider opportunities for improvement/optimization for cost savings or part substitution. Additionally, an engineering team may revisit a design after production. Extreme changes can be costly and time-consuming; minor adjustments periodically are more economical and improve the design while maintaining user familiarity.

Design optimization may look like:

Performance Tuning
Adjusting operational parameters to achieve optimal performance and minimize unwanted vibrations, such as balancing rotating components and fine-tuning operational speeds.

Enhancing User Comfort
Improving user experience by reducing perceptible vibrations, such as ergonomic adjustments and noise reduction.

Energy Efficiency
Identifying and mitigating sources of vibrational energy loss, such as implementing efficient design solutions.

Cost Savings
“Decontenting” unnecessary structural materials or using alternate materials.

Modifying the design

Regarding a true fail, a previous lesson stated:

“There is often significant organizational pushback when engineers identify test failures. With irrefutable recorded data to correlate the operational environment and established test acceleration methodologies, an engineer should have no problem convincing an organization that a design change is necessary to avert future issues.”

Often, an engineer requires additional insight into the product behavior to modify the design. More advanced analysis techniques, such as modal analysis or fatigue analysis, can provide additional data for informed design modifications.

Product Improvement

There is a myriad of ways an engineer might improve a design based on their test results and troubleshooting, including:

Identifying Weak Points

Stress Concentration
Locate any points of high stress that lead to material fatigue

Resonance Frequencies
Identify any resonant frequencies that amplify vibrations

Component Interaction
Assess component interaction and identify any weak points

Operational Conditions
Determine if operational conditions (e.g., load, speed) affect product behavior

Material and Design Modifications

Damping Materials
Introduce materials that absorb and dissipate vibration

Reinforcement
Strengthen weak points with additional supports or thicker materials

Component Redesign
Shift natural frequencies away from operational ranges

Material Substitution
Replace existing materials with ones that have better vibration resistance properties

Improving Durability

Fatigue Analysis
Estimate the lifespan of components under cyclic loading

Thermal Effects
Consider the combined effects of vibration and temperature on material properties

Corrosion Resistance
Identify how vibrations may accelerate corrosion

Environmental Testing
Conduct tests in varied environmental conditions (humidity, temperature) to ensure durability

Optimizing Design for Manufacturing

Simplifying Design
Streamline design, reducing the number of parts and potential failure points

Cost-benefit Analysis
Balance the cost of design modifications with the benefits of improved performance

Standardization
Use vibration-resistant designs that can be standardized across different product lines

Ease of Assembly
Design components to minimize the impact of assembly tolerances on vibration performance