Strength at Yield (Tensile)

Mechanical Properties of Plastics

Tensile Strength at YieldWhat is tensile strength? Tensile strength is an ability of plastic material to withstand maximum amount of tensile stress while being pulled or stretched without failure. It is the point when a material goes from elastic to plastic deformation.

  • Elastic deformation - When the stress is removed, the material returns to the dimension it had before the load was applied. Valid for small strains (except the case of rubbers). Deformation is reversible, non-permanent
  • Plastic deformation -When the stress is removed, the material does not return to its previous dimension but there is a permanent, irreversible deformation.

Tensile strength is often referred to as ultimate tensile strength and is measured in units of force per cross-sectional area.

There are three types of tensile strength (See Graph 1 below):

  • Yield strength (A) - The stress a material can withstand without permanent deformation
  • Ultimate strength (B) - The maximum stress a material can withstand
  • Breaking strength (C) - The stress coordinate on the stress-strain curve at the point of rupture

In other words, materials first deform elastically - when you release the stress they return to their original shape. Then with more force they deform plastically, this is yield - when you release the stress they have permanently been stretched into a new shape. Finally, they break; this is ultimately tensile stress, or breaking point.

 » Select the Suitable Plastic with 'Good Tensile Strength' Meeting your Requirement 

Tensile strength (TS) at yield, sometimes called tensile stress at yield, measures the stress a plastic can withstand at the yield point, i.e. when an increase in strain is not provoked by an increase of stress. It is an important for a material that is going to be stretched or under tension. For structural applications, the yield stress is usually a more important property than the tensile strength, since once it is passed, the structure has deformed beyond acceptable limits.

Hence, it is one of the important mechanical properties for:

  • Material evaluation
  • Quality control
  • Structure design
  • Modeling, and
  • Failure analysis

Check out more on Tensile strength at yield:

 » Strength at Yield (Tensile)– Property values for several plastics
 » Difference between tensile strength and yield strength
 » How to measure tensile properties of plastics?
 » Significance of tensile properties and factors affecting tensile strength of plastics

Yield Strength vs. Tensile Strength

Yield Strength is the stress a material can withstand without permanent deformation or a point at which it will no longer return to its original dimensions (by 0.2% in length). Whereas, Tensile Strength is the maximum stress that a material can withstand while being stretched or pulled before failing or breaking.

  • Yield Strength can be seen on a stress-strain curve as the point where the graph is no longer linear.
  • Since it is quite difficult to determine an exact point where a line stops being linear, Yield Strength is usually the point where the value on the stress-strain curve is 0.2% off from what it would be if it was completely linear
Stress-Strain Graph
Typical Stress-Strain Curve

Stress-Strain Curve

When a stretching force (tensile force) is applied to an object, it extends, and its behavior can be obtained using stress-strain curve in the elastic deformation region (Known Hooke’s Law). The extension that a force produces is not only dependent on the material but also on other factors like dimensions of the object (e.g. length, thickness etc.)

Stress is defined as the force per unit area of plastic and has units Nm-2 or Pa. The formula to calculate tensile stress is:

σ (stress) = F/A

Where σ is stress (in Newtons per square metre or, equivalently, Pascals), F is force (in Newtons, commonly abbreviated N), and A is the cross-sectional area of the sample.

While, Strain is defined as extension per unit length. And, since it is a ratio of lengths, strain has no units.

ε (strain) = ΔL/L0;    ΔL = L-L0

Where L0 is the original length of a bar being stretched, and L is its length after it has been stretched. ΔL is the extension of the bar, the difference between these two lengths.

Learn More about Other Mechanical Properties: Young’s Modulus, Toughness, Hardness, Elongation at Yield, Elongation at Break, Strength at Break(Tensile)

Units to Measure Tensile Strength

In the International System, the unit of Tensile Strength is the pascal (Pa) (or megapascals, MPa or even GPa, megapascals), which is equivalent to newtons per square meter (N/m2).

In the US, pounds-force per square inch (lbf/in2 or psi), or kilo-pounds per square inch (kpsi) are commonly used for convenience when measuring tensile strengths.

NOTE: In engineering, strength and stiffness are concepts which are confuse often. For the right material classification, read about “Stiffness” here.

Stress-Strain Plots of Plastics
Stress-Strain Plots for a Typical Elastomer, Flexible Plastics, Rigid Plastic, and Fiber
(Source: Principles of Polymerization, Fourth Edition, George Odian)

How to Measure Tensile Properties of Plastics?

Tensile tests measure the force required to break a specimen and the extent to which the specimen stretches or elongates to that breaking point.

In general, “tensile test methods” are applied to measure the tensile properties of plastics. The common methods used are:

  • ASTM D638 - Standard Test Method for Tensile Properties of Plastics
  • ISO 527-1:2012 - Determination of tensile properties. General principles

Of course, there exists several other methods as well as listed below, but they are not discussed here.

ASTM D638 and ISO 527 Test Methods

ASTM D638 and ISO 527 test methods cover the determination of the tensile properties of plastics and plastic composites under defined conditions in the form of standard dumbbell-shaped test specimens. The defined conditions can range from pretreatment, temperature, humidity, to testing machine speed.

The methods are used to investigate the tensile behavior of the test specimens.

Watch this Interesting Video on Micro Tensile Strength Test of Plastics per ASTM D638

Source: ADMET

And, the following calculations can be made from tensile test results:

For ASTM D638 the test speed is determined by the material specification. For ISO 527 the test speed is typically 5 or 50mm/min for measuring strength and elongation and 1mm/min for measuring modulus.

An extensometer is a device that is used to measure changes in the length of an object. It is useful for stress-strain measurements and tensile tests.

Significance of Tensile Properties

  • Tensile properties provide useful data for plastics engineering design purposes.
  • Tensile properties frequently are included in material specifications to ensure quality.
  • Tensile properties often are measured during development of new materials and processes, so that different materials and processes can be compared.
  • Finally, tensile properties often are used to predict the behavior of a material under forms of loading other than uniaxial tension.

Factors Affecting Tensile Strength of Plastics

Tensile Strength of PlasticsThe strength of polymers is further governed by their:

  • Molecular Weight: The strength of the polymer rises with increase in molecular weight and reaches the saturation level at some value of the molecular weight.
    • At lower molecular weight - the polymer chains are loosely bonded by weak van der Waals forces and the chains can move easily, responsible for low strength, although crystallinity is present
    • At higher molecular weight polymer - The polymer chains become large and hence are crosslinked, giving strength to the polymer

  • Cross-linking: The cross-linking restricts the motion of the chains and increases the strength of the polymer.

  • Crystallinity: The crystalline phase of polymer increases strength; hence the intermolecular bonding is more significant. Therefore, the polymer deformation can result in the higher strength leading to oriented chains.

Other than that velocity of testing, orientation level of fibers, temperature, filler content etc. also impact tensile strength values of thermoplastics.

Find commercial grades matching your mechanical properties target using "Property Search - Tensile strength at yield" filter in Omnexus Plastics Database:

Omnexus Plastics Database - Property Search

Strength at Yield (Tensile) Values of Several Plastics

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Polymer Name Min Value (MPa) Max Value (MPa)
ABS - Acrylonitrile Butadiene Styrene 29.6 48.0
ABS Flame Retardant 25.0 50.0
ABS High Heat 30.0 50.0
ABS High Impact 20.0 40.0
ABS/PC Blend - Acrylonitrile Butadiene Styrene/Polycarbonate Blend 45.0 55.0
ABS/PC Blend 20% Glass Fiber 75.0 80.0
ABS/PC Flame Retardant 50.0 60.0
Amorphous TPI Blend, Ultra-high heat, Chemical Resistant (High Flow) 112.0 112.0
Amorphous TPI, High Heat, High Flow, Lead-Free Solderable, 30% GF 147.0 147.0
Amorphous TPI, High Heat, High Flow, Transparent, Lead-Free Solderable (High Flow) 101.0 101.0
Amorphous TPI, High Heat, High Flow, Transparent, Lead-Free Solderable (Standard Flow) 101.0 101.0
Amorphous TPI, Moderate Heat, Transparent 95.0 95.0
Amorphous TPI, Moderate Heat, Transparent (Food Contact Approved) 95.0 95.0
Amorphous TPI, Moderate Heat, Transparent (Mold Release grade) 95.0 95.0
Amorphous TPI, Moderate Heat, Transparent (Powder form) 95.0 95.0
ASA - Acrylonitrile Styrene Acrylate 35.0 40.0
ASA/PC Blend - Acrylonitrile Styrene Acrylate/Polycarbonate Blend 50.0 65.0
ASA/PC Flame Retardant 58.0 58.0
ASA/PVC Blend - Acrylonitrile Styrene Acrylate/Polyvinyl Chloride Blend 45.0 50.0
CA - Cellulose Acetate 19.0 43.0
CAB - Cellulose Acetate Butyrate 16.0 43.0
CP - Cellulose Proprionate 22.0 50.0
CPVC - Chlorinated Polyvinyl Chloride 40.0 55.0
ETFE - Ethylene Tetrafluoroethylene 42.0 42.0
ECTFE 29.0 32.0
EVA - Ethylene Vinyl Acetate 7.00 40.0
EVOH - Ethylene Vinyl Alcohol 50.0 94.0
HDPE - High Density Polyethylene 25.0 30.0
HIPS - High Impact Polystyrene 20.0 40.0
HIPS Flame Retardant V0 20.0 30.0
Ionomer (Ethylene-Methyl Acrylate Copolymer) 3.1 30.0
LCP - Liquid Crystal Polymer 175.0 175.0
LCP Carbon Fiber-reinforced 190.0 240.0
LCP Glass Fiber-reinforced 160.0 220.0
LCP Mineral-filled 110.0 180.0
LDPE - Low Density Polyethylene 10.0 20.0
LLDPE - Linear Low Density Polyethylene 10.0 30.0
MABS - Transparent Acrylonitrile Butadiene Styrene 42.0 48.0
PA 11 - (Polyamide 11) 30% Glass fiber reinforced 32.0 40.0
PA 11, Conductive 23.0 40.0
PA 11, Flexible 25.0 27.0
PA 11, Rigid 40.0 45.0
PA 12 (Polyamide 12), Conductive 32.0 -
PA 12, Fiber-reinforced 23.0 40.0
PA 12, Flexible 23.0 24.0
PA 12, Glass Filled 39.0 49.0
PA 12, Rigid 38.0 44.0
PA 46 - Polyamide 46 65.0 85.0
PA 46, 30% Glass Fiber 128.0 132.0
PA 6 - Polyamide 6 50.0 90.0
PA 6-10 - Polyamide 6-10 50.0 65.0
PA 66 - Polyamide 6-6 45.0 85.0
PA 66, 30% Glass Fiber 100.0 125.0
PA 66, 30% Mineral filled 148.0 1152.0
PA 66, Impact Modified, 15-30% Glass Fiber 90.0 120.0
PA 66, Impact Modified 35.0 50.0
Polyamide semi-aromatic 70.0 78.0
PAI - Polyamide-Imide 150.0 150.0
PAI, 30% Glass Fiber 210.0 210.0
PAI, Low Friction 125.0 165.0
PAN - Polyacrylonitrile 50.0 65.0
PAR - Polyarylate 69.0 69.0
PBT - Polybutylene Terephthalate30% Glass Fiber 135.0 140.0
PC (Polycarbonate) 20-40% Glass Fiber 90.0 160.0
PC (Polycarbonate) 20-40% Glass Fiber Flame Retardant 90.0 140.0
PC - Polycarbonate, high heat 61.0 69.0
PCL - Polycaprolactone 24.0 25.0
PE - Polyethylene 30% Glass Fiber 52.0 63.0
PE/TPS - Thermoplastic Starch 30.0 55.0
PEEK - Polyetheretherketone 90.0 110.0
PEEK 30% Carbon Fiber-reinforced 200.0 220.0
PEEK 30% Glass Fiber-reinforced 150.0 180.0
PEI - Polyetherimide 100.0 110.0
PEI, 30% Glass Fiber-reinforced 150.0 160.0
PEI, Mineral Filled 90.0 100.0
PEKK (Polyetherketoneketone), Low Cristallinity Grade 100.0 105.0
PESU - Polyethersulfone 80.0 90.0
PESU 10-30% glass fiber 75.0 140.0
PET - Polyethylene Terephthalate 50.0 57.0
PET, 30% Glass Fiber-reinforced 130.0 150.0
PET, 30/35% Glass Fiber-reinforced, Impact Modified 100.0 110.0
PETG - Polyethylene Terephthalate Glycol 50.0 51.0
PE-UHMW - Polyethylene -Ultra High Molecular Weight 20.0 25.0
PFA - Perfluoroalkoxy 15.0 30.0
PI - Polyimide 120.0 120.0
PLA - Polylactide 59.0 61.0
PLA - injection molding 48.0 52.0
PMMA - Polymethylmethacrylate/Acrylic 38.0 70.0
PMMA (Acrylic) High Heat 65.0 79.0
PMP - Polymethylpentene 16.0 18.0
PMP 30% Glass Fiber-reinforced 60.0 68.0
PMP Mineral Filled 17.0 18.0
Polyamide 66 (Nylon 66)/Carbon Fiber, Long, 30% Filler by Weight 290.0 290.0
Polyamide 66 (Nylon 66)/Carbon Fiber, Long, 40% Filler by Weight 305.0 305.0
Polyamide 66 (Nylon 66)/Glass Fiber, Long, 40% Filler by Weight 230.0 230.0
Polyamide 66 (Nylon 66)/Glass Fiber, Long, 40% Filler by Weight 210.0 210.0
Polyamide 66 (Nylon 66)/Glass Fiber, Long, 50% Filler by Weight 270.0 270.0
Polyamide 66 (Nylon 66)/Glass Fiber, Long, 50% Filler by Weight 230.0 230.0
Polyamide 66 (Nylon 66)/Glass Fiber, Long, 60% Filler by Weight 270.0 270.0
Polyamide 66 (Nylon 66)/Glass Fiber, Long, 60% Filler by Weight 250.0 250.0
Polypropylene Homopolymer (PP Homopolymer)/Glass Fiber, Long, 30% Filler by Weight 120.0 120.0
Polypropylene Homopolymer (PP Homopolymer)/Glass Fiber, Long, 40% Filler by Weight 130.0 130.0
Polypropylene Homopolymer (PP Homopolymer)/Glass Fiber, Long, 40% Filler by Weight 120.0 120.0
Polypropylene Homopolymer (PP Homopolymer)/Glass Fiber, Long, 50% Filler by Weight 130.0 130.0
Polypropylene Homopolymer (PP Homopolymer)/Glass Fiber, Long, 50% Filler by Weight 130.0 130.0
POM - Polyoxymethylene (Acetal) 54.0 78.0
POM (Acetal) Impact Modified 35.0 50.0
POM (Acetal) Low Friction 48.0 69.0
POM (Acetal) Mineral Filled 50.0 75.0
PP - Polypropylene 10-20% Glass Fiber 35.0 56.0
PP, 10-40% Mineral Filled 19.0 27.0
PP, 10-40% Talc Filled 22.0 28.0
PP, 30-40% Glass Fiber-reinforced 42.0 70.0
PP (Polypropylene) Copolymer 20.0 35.0
PP (Polypropylene) Homopolymer 35.0 40.0
PP, Impact Modified 11.0 28.0
PPE - Polyphenylene Ether 45.0 65.0
PPE, 30% Glass Fiber-reinforced 100.0 130.0
PPE, Flame Retardant 45.0 65.0
PPE, Impact Modified 50.0 56.0
PPE, Mineral Filled 65.0 75.0
PPS - Polyphenylene Sulfide 50.0 80.0
PPS, 20-30% Glass Fiber-reinforced 130.0 150.0
PPS, 40% Glass Fiber-reinforced 120.0 150.0
PPS, Conductive 60.0 140.0
PPS, Glass fiber & Mineral-filled 60.0 150.0
PPSU - Polyphenylene Sulfone 70.0 76.0
PS (Polystyrene) 30% glass fiber 70.0 70.0
PS (Polystyrene) Crystal 35.0 60.0
PS, High Heat 40.0 60.0
PSU - Polysulfone 69.0 80.0
PSU, 30% Glass fiber-reinforced 100.0 125.0
PSU Mineral Filled 65.0 70.0
PTFE - Polytetrafluoroethylene 9.0 30.0
PVC (Polyvinyl Chloride), 20% Glass Fiber-reinforced 60.0 90.0
PVC, Plasticized 4.0 7.0
PVC, Plasticized Filled 10.0 25.0
PVC Rigid 35.0 50.0
PVDC - Polyvinylidene Chloride 20.0 30.0
PVDF - Polyvinylidene Fluoride 20.0 56.0
SAN - Styrene Acrylonitrile 65.0 85.0
SAN, 20% Glass Fiber-reinforced 100.0 120.0
SMA - Styrene Maleic Anhydride 35.0 50.0
SMA, 20% Glass Fiber-reinforced 56.0 75.0
SMA, Flame Retardant V0 20.0 25.0
SMMA - Styrene Methyl Methacrylate 36.0 85.0
TPI-PEEK Blend, Ultra-high heat, Chemical Resistant, High Flow, 240C UL RTI 105.0 105.0
TPS/PE - Thermoplastic Starch/ Polyethylene Blend (30 micron films tested) 25.0 25.0
TPS-Injection General Purpose, Starch GP 19.0 45.0
TPS-Injection Water Resistant, Starch WR 7.0 11.0

Commercially Available Polymer Grades with High Tensile Strength

Learn More about Other Mechanical Properties: Young’s Modulus, Toughness, Hardness, Elongation at Yield, Elongation at Break, Strength at Break (Tensile)

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