PEEK Tensile Strength Guide

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Understanding PEEK Tensile Strength: Effects of Temperature, Environment, and Reinforcement

Polyether Ether Ketone (PEEK) is one of the strongest and most reliable high-performance thermoplastics, widely used in aerospace, medical, semiconductor, automotive, and energy applications. Tensile strength is one of the most important mechanical properties engineers consider when selecting PEEK for load-bearing or high-temperature parts.

Unfilled PEEK typically provides tensile strength in the range of 90–105 MPa, depending on grade and processing. Reinforced versions—such as 30% carbon fiber (CF30) and 30% glass fiber (GF30)—offer significantly different strength behaviors and performance advantages. Understanding how temperature, chemical environment, and reinforcement influence tensile performance is essential for designing durable and stable PEEK components.

How Temperature Affects PEEK Tensile Strength

PEEK maintains strong mechanical properties at temperatures where many engineering plastics soften or degrade. However, tensile strength steadily declines as temperature approaches the material’s glass transition temperature (approximately 143°C).

Key temperature effects include:

  • Room temperature: Unfilled PEEK provides maximum tensile performance.

  • 100–150°C range: Noticeable decrease in strength; reinforced grades (CF30/GF30) perform significantly better.

  • Above Tg: Tensile strength drops more rapidly as polymer chains gain mobility.

  • Near melting temperature (340°C): The material loses structural load-bearing capability.

For continuous service above 120°C, engineers often choose carbon fiber reinforced grades for better retention of mechanical properties.

Influence of Environmental Factors

1. Chemical Exposure

PEEK has excellent chemical resistance to fuels, oils, solvents, and most acids. However, extended exposure to strong acids, halogens, or oxidative environments at elevated temperatures may affect its mechanical performance.

2. Moisture

PEEK has very low moisture absorption, meaning humidity has minimal effect on tensile strength. Even in steam or hot-water environments, PEEK retains most of its mechanical integrity.

3. Radiation & Sterilization

Different sterilization methods (gamma, autoclave, EtO) can impact tensile properties over time. Carbon-filled grades typically resist radiation effects better than unfilled or glass-filled versions.

PEEK CF30 vs GF30: Tensile Strength Differences

PEEK’s tensile behavior changes dramatically when reinforced with fibers. The two most common reinforced grades—CF30 and GF30—serve different engineering purposes.

PEEK CF30 (30% Carbon Fiber)

  • Higher tensile strength than unfilled PEEK (commonly over 120 MPa).

  • Much higher tensile modulus due to stiff carbon fibers.

  • Better retention of strength at elevated temperatures.

  • Lower elongation and stronger anisotropy depending on fiber orientation.

  • Ideal for load-bearing, structural, or high-temperature components.

PEEK GF30 (30% Glass Fiber)

  • Tensile strength improvement compared to unfilled PEEK, but lower than CF30.

  • Increased stiffness and dimensional stability.

  • Excellent cost-to-performance ratio.

  • Slightly higher density than CF30.

  • Better for housings, insulators, brackets, and components requiring stable dimensions across temperature changes.

Processing and Microstructure Effects on Tensile Performance

The tensile strength of PEEK components is strongly influenced by processing conditions:

  • Crystallinity: Higher crystallinity increases tensile modulus and heat resistance.

  • Cooling rate: Slow, controlled cooling improves mechanical stability; rapid cooling may reduce strength.

  • Annealing: Relieves internal stresses and increases crystallinity for more consistent tensile behavior.

  • Fiber orientation (in CF30/GF30): Mechanical performance is directional; strength is highest along fiber orientation.

  • Manufacturing method: Injection molding, compression molding, and machining from extruded stock can all produce different tensile values.

Proper processing is essential to achieve the expected tensile performance from the chosen PEEK grade.

Long-Term Tensile Behavior: Creep and Fatigue

PEEK exhibits excellent creep resistance compared with typical engineering plastics. However:

  • Higher temperatures accelerate creep.

  • Reinforced grades (especially CF30) significantly reduce creep deformation under sustained loads.

  • Fatigue performance is generally strong, making PEEK suitable for dynamic or cyclic load applications.

For components in continuous service above 100°C, reinforced PEEK grades are strongly recommended to maintain long-term mechanical stability.

Conclusion

PEEK is a high-performance material with outstanding tensile strength, especially when compared to other engineering plastics. Its performance depends on several key factors—temperature, environment, and reinforcement. Carbon-fiber-reinforced PEEK (CF30) offers the best tensile strength and stiffness for demanding load-bearing and high-temperature applications, while glass-fiber-reinforced PEEK (GF30) provides an excellent balance of strength, stability, and cost.

Selecting the right PEEK grade—and optimizing processing and design conditions—ensures components deliver the mechanical stability and long-term reliability required for advanced engineering applications.

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