Short answer

Designers should prioritize strategies that reinforce the foam's internal structure against mechanical failure rather than focusing on gas retention.

Field: Final Production
Source: University of Birmingham Institutional Research Archive (University of Birmingham) (2004)
Method: Experimental and Theoretical Analysis
Evidence: Strong effect

The primary cause of cushioning degradation in EVA foams used in running shoes is the physical deformation and failure of the cellular structure under repeated impact, rather than the diffusion of gas from the foam. This final production research insight is drawn from a 2004 study published in University of Birmingham Institutional Research Archive (University of Birmingham). Using Experimental and theoretical analysis, researchers explored how this design variable affects real-world outcomes. The key design takeaway: Designers should prioritize strategies that reinforce the foam's internal structure against mechanical failure rather than focusing on gas retention.

Study

Final ProductionHigh ImpactStrong effect

EVA foam cushioning degrades due to structural yielding, not gas loss, after 500km of running.

University of Birmingham Institutional Research Archive (University of Birmingham) · 2004

Key Findings

01The softening and reduction in cushioning properties of EVA foams in running shoes are primarily caused by the yielding and unyielding of the cellular structure.
02Gas loss due to diffusion in EVA foams under cyclic loads is negligible.
03Controlled running tests confirmed midsole foam deterioration, leading to increased peak plantar pressure and structural damage.

Application

Design takeaway

Designers should prioritize strategies that reinforce the foam's internal structure against mechanical failure rather than focusing on gas retention.

How to apply

When designing or selecting midsole materials for athletic footwear, prioritize materials and structures that demonstrate high resistance to cellular deformation and fatigue under repeated impact.

Project actions

01When testing materials for cushioning, consider simulating repeated impacts rather than just static compression.
02Investigate the micro-structure of foam materials to understand how their cellular arrangement affects durability.

Method & Evidence

AimTo investigate the primary mechanisms responsible for the degradation of cushioning properties in EVA foams used in running shoes over their lifespan.

MethodExperimental and Theoretical Analysis

ProcedureA specialized repeat impact machine was developed to simulate the loading conditions experienced by running shoe midsoles. The mechanical response of EVA foams was analyzed before and after simulated use. Diffusion coefficients of EVA foams were measured using a microbalance under controlled temperature and pressure. Theoretical analysis of gas diffusion in foams under cyclic loads was also performed. Controlled running tests were conducted to validate findings in a real-world context, measuring peak plantar pressure and structural damage.

ContextSports footwear design, material science for polymers

Variables

IVNumber of impact cycles, distance run (in controlled tests)

DVCushioning properties (e.g., peak plantar pressure, material softening), structural integrity of the foam

CVType of EVA foam, temperature, pressure (during diffusion tests), impact energy (in repeat impact machine)

Strengths & Limitations

Strengths

+Development of a specialized testing apparatus (repeat impact machine) for more relevant simulation.
+Combination of experimental testing, theoretical analysis, and real-world validation (controlled running tests).

Limitations

It's difficult to perfectly replicate the complex forces and environmental conditions of real-world use in a controlled experiment.

Reliability & validity

The development of a reproducible testing machine and confirmation of findings through controlled running tests enhance the reliability and validity of the results regarding the primary degradation mechanism.

Think critically

If gas diffusion is negligible, what other environmental factors (e.g., moisture, temperature fluctuations, chemical exposure) might contribute to EVA foam degradation in running shoes?

Design Principles

"Material degradation in cellular foams under cyclic loading is predominantly governed by mechanical fatigue of the cell walls and structure."

Understanding the true mechanisms of material degradation is crucial for designing more durable and effective footwear. This insight guides material selection and structural design to enhance longevity and performance, impacting user experience and product lifecycle.

What This Means for Your Design

The foam in your running shoes gets less bouncy because its internal structure gets squashed and damaged over time, not because the air leaks out.

How to use in your project

1.Use this research to justify your choice of materials or design features aimed at improving durability in your design project.

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Quick Cite

Paragraph starter

Research indicates that the degradation of cushioning in EVA foams, commonly used in running shoes, is primarily attributed to the mechanical yielding and failure of its cellular structure under repeated impact, rather than significant gas diffusion. This suggests that design efforts should focus on enhancing the structural integrity and fatigue resistance of the foam's internal matrix to improve product durability.

Source

University of Birmingham Institutional Research Archive (University of Birmingham)

Gas loss and durability of EVA foams used in running shoes

journal · 2004

View source

Questions About This Research

What does the research say about eva foam cushioning degrades due to structural yielding, not gas loss, after 500km of running?: Designers should prioritize strategies that reinforce the foam's internal structure against mechanical failure rather than focusing on gas retention. Evidence: University of Birmingham Institutional Research Archive (University of Birmingham) (2004).
Why does "EVA foam cushioning degrades due to structural yielding, not gas loss, after 500km of running." matter for design?: Understanding the true mechanisms of material degradation is crucial for designing more durable and effective footwear. This insight guides material selection and structural design to enhance longevity and performance, impacting user experience and product lifecycle.
How can designers apply this research?: Designers should prioritize strategies that reinforce the foam's internal structure against mechanical failure rather than focusing on gas retention.
What were the main findings?: The softening and reduction in cushioning properties of EVA foams in running shoes are primarily caused by the yielding and unyielding of the cellular structure.. Gas loss due to diffusion in EVA foams under cyclic loads is negligible.. Controlled running tests confirmed midsole foam deterioration, leading to increased peak plantar pressure and structural damage.
What research method was used?: Experimental and Theoretical Analysis.
How strong is the evidence?: Evidence strength is rated Strong effect, based on a 2004 journal from University of Birmingham Institutional Research Archive (University of Birmingham).
What should I do differently in my next project?: When designing or selecting midsole materials for athletic footwear, prioritize materials and structures that demonstrate high resistance to cellular deformation and fatigue under repeated impact.
What are the limitations?: The study focused specifically on EVA foams; findings may vary for other foam types. The simulated impact conditions might not perfectly replicate all aspects of real-world running. Long-term effects beyond the tested duration were not explicitly studied.