Performance Parameters of Ultra-High Molecular Weight Polyethylene (UHMWPE) and Their Meanings 

Tensile Strength The maximum tensile stress that a specimen can withstand until fracture during a tensile test. The result is expressed in kilograms-force per square centimeter (kgf/cm²) or pascals (Pa), calculated based on the original cross-sectional area of the specimen at the fracture point.

Young's Modulus The elastic modulus under tensile load, representing the ratio of tensile stress to the corresponding strain within the proportional limit. It is expressed in kilograms-force per square centimeter (kgf/cm²) or pascals (Pa).

Elastic Limit The maximum stress a material can withstand without leaving any permanent deformation. It is expressed in kilograms per square centimeter (kgf/cm²) or pascals (Pa). Note: During actual strain measurement, a small load rather than zero load is often used as the final or initial reference load.

Elastic Modulus Within the proportional limit, the ratio of stress (such as tensile, compressive, bending, torsional, or shear stress) to the corresponding strain in a material. It is expressed in kilograms-force per square centimeter (kgf/cm²) or pascals (Pa).

Impact Strength

1. The maximum capacity of a material to withstand impact load.

2. The ratio of the energy absorbed by a material during fracture under impact load to the cross-sectional area of the specimen. It is expressed in kilogram-force centimeters per square centimeter (kgf·cm/cm²) or newton-meters per square meter (N·m/m²).

Flexural Strength The maximum stress a material can withstand at the point of rupture or at a specified deflection under a bending load. It is expressed in kilograms-force per square centimeter (kgf/cm²) or pascals (Pa).

Vicat Softening Point Test A test method to evaluate the tendency of thermoplastic materials to deform at high temperatures. Under conditions of a constant heating rate, a flat-ended needle with a specified load and a cross-sectional area of 1 mm² is placed on the specimen. The temperature at which the needle penetrates the specimen by 1 mm is recorded as the Vicat softening temperature.

Hardness The ability of UHMWPE to resist indentation and scratching. Note: Different testing methods yield various hardness values, including Barcol hardness, Brinell hardness, Rockwell hardness, Shore hardness, Mohs hardness, scratch hardness, and Vickers hardness.

Yield Stress The stress at the yield point on the stress-strain curve.

Stress The force applied per unit area on a material. It is expressed in kilograms-force per square centimeter (kgf/cm²) or pascals (Pa). Note: If the unit area is calculated based on the original cross-sectional area, the resulting stress is engineering stress; if calculated based on the instantaneous cross-sectional area during deformation, it is true stress. Types of stress include shear stress, tensile stress, and compressive stress.

Stress Cracking The phenomenon where cracks form on the external or internal surfaces of a plastic material due to prolonged or repeated application of stress below the material's mechanical strength. Note: The stress causing cracking can be internal or external, or a combination of both, and the rate of stress cracking varies with the environmental conditions.

Internal Stress The stress within a material in the absence of external force, caused by improper processing, temperature changes, solvent effects, etc.

Stress-Strain Curve A graph plotting stress (vertical axis) against strain (horizontal axis) during material testing.

Yield Point The first point on the stress-strain curve where stress does not increase with strain. At the yield point, the specimen begins to undergo permanent deformation. The stress can be tensile, compressive, or shear stress.

Creep The phenomenon where the strain in a material changes over time under a constant stress. Note: Instantaneous strain is not included.

Creep Recovery The portion of deformation that decreases over time after the load is removed from the specimen.

Fatigue Limit The maximum stress in a fatigue test at which the specimen does not fail after an infinite number of stress cycles. Note: Many plastics do not exhibit a true fatigue limit. Therefore, the stress level at which 50% of specimens do not fail after 10⁷ to 10⁸ cycles is used to represent the fatigue limit.

Fatigue Life The number of stress or strain cycles a specimen can withstand under alternating cyclic stress or strain before failure.

Haze The cloudy or turbid appearance caused by light scattering within or on the surface of transparent or translucent plastics. It is expressed as a percentage of the forward-scattered light flux to the transmitted flux.

Light Transmittance The percentage of light flux transmitted through a transparent or translucent material relative to the incident light flux.

Transparency The property of a material that allows visible light to pass through with minimal scattering.

Oil Resistance The ability of a plastic to resist dissolution, swelling, cracking, deformation, or deterioration of physical properties caused by exposure to oils.

Coefficient of Linear Expansion The percentage change in length of a material for every degree of temperature change.