- What is elongation at yield?
- What is the formula of elongation at yield?
- What is the importance of elongation at yield?
- Which materials show high elongation?
- What factors affect the elongation at yield?
- What are the test methods to calculate elongation?
- Which instrument measures elongation at yield?
- What is the elongation at yield values of several plastics?
What is elongation at yield?
Elongation at Yield is the ratio between increased length and initial length at the yield point. In an ASTM test of tensile strength, the test specimen is pulled from both ends. As the pulling progresses, the specimen bar elongates at a uniform rate. This elongation is proportionate to the rate at which the load or pulling force increases.
Beyond the proportional limit & elastic stress limit, further pulling of the specimen in the opposite direction causes:
-
permanent elongation or
- deformation of the specimen
There is a point when an increase of strain is not provoked by an increase of stress on the test specimen i.e., beyond which the plastic material stretches briefly without a noticeable increase in load. This point is known as the yield point. Elongation at yield is the ability of a plastic specimen to resist changes of shape before it deforms irreversibly.
Graph depicting the typical stress vs. strain curve of plastics
What is the formula of elongation at yield?
Elongation at yield is the deformation of plastic material at the yield point. It is the relative increase in length.
ɛ = (ΔL/L) x 100
Where:
-
ɛ is the elongation
- ΔL is the final length
- L is the initial length
We can measure Elongation at Yield in % (% of elongation vs. initial size at yield point). It is also called tensile elongation at yield.
What is the importance of elongation at yield?
Elongation at Yield is an important mechanical property of materials.
- It measures the load a material can withstand at the yield point before breaking.
- Used in components that absorb energy by plastic deformation.
Which materials show high elongation?
Ultimate elongation values of 100% are common for elastomers and film/packaging polyolefins. Rigid plastics, especially fiber-reinforced ones, often exhibit values under 5%. Materials that show high elongation are:
- Thermoplastics with High Elongation – View Products
- TPEs/TPVs with High Elongation – View Products
- Rubbers with High Elongation – View Products
- Thermosets with High Elongation – View Products
What factors affect the elongation at yield?
-
Velocity of Testing: Slow testing allows for polymer relaxation and higher elongation values.
- Orientation Level: Fibers that are less oriented tend to exhibit greater degrees of elongation.
- Temperature: In general, the elongation increases with an increase in temperature.
- Filler Content: The elongation of composites decreases with an increase in the filler content.
What are the test methods to calculate elongation?
Tensile tests measure the force required to break a specimen. It also determines the extent to which the specimen stretches or elongates to that breaking point.
In general, “tensile test methods” measure the modulus of elasticity of materials. 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
These methods determine the tensile properties of plastics and plastic composites. This is done under defined conditions that can range from:
- pretreatment,
- temperature,
- humidity, and
- machine speed
The test specimens are in the form of a standard dumbbell shaped.
For ASTM D638, the test speed is determined by the material specification. For ISO 527, the test speed is typically 5 or 50 mm/min for measuring strength and elongation, and 1 mm/min for measuring modulus.
Apart from Elongation at Yield, the tensile test results can also calculate:
Which instrument is used to determine elongation at yield?
An extensometer determines the elongation and tensile modulus. It is a device that measures the changes in the length of an object. It evaluates the stress-strain curve values.
The two main types of extensometers are contact and non-contact.
- Contact extensometers are further divided into two types:
-
Clip-on extensometer: They can measure displacements from very small to relatively large. That is from less than 1 mm to over 100 mm. Used for applications requiring high-precision strain measurement (most ASTM-based tests). Major advantages include:
- Automated testing clip-ons: They replace digital "sensor arm" extensometers. They can be applied to the specimen automatically by a motorized system. They produce much more repeatable results than traditional clip-on devices. They measure very high extensions (up to 1000 mm) without losing any accuracy. Major advantages include:
-
Better linearity,
- reduced signal noise, and
- synchronization with the corresponding force data.
- Non-contact extensometers: These devices are beginning to bring advantages for certain applications. Especially, in industries where it is impractical to use contact extensometers.
What is the elongation at yield values for several plastics?
Click to find polymer you are looking for:
A-C |
E-M |
PA-PC |
PE-PL |
PM-PP |
PS-X
| Polymer Name |
Min Value (%) |
Max Value (%) |
| ABS - Acrylonitrile Butadiene Styrene |
1.70 |
6.00 |
| ABS Flame Retardant |
2.10 |
2.20 |
| ABS High Heat |
2.10 |
2.80 |
| ABS/PC Blend - Acrylonitrile Butadiene Styrene/Polycarbonate Blend |
3.00 |
5.00 |
| ABS/PC Blend 20% Glass Fiber |
1.90 |
2.20 |
| ABS/PC Flame Retardant |
70.0 |
4.00 |
| ASA - Acrylonitrile Styrene Acrylate |
3.10 |
3.50 |
| ASA/PC Blend - Acrylonitrile Styrene Acrylate/Polycarbonate Blend |
4.00 |
4.00 |
| ASA/PC Flame Retardant |
5.00 |
5.00 |
| CA - Cellulose Acetate |
3.10 |
3.50 |
| CAB - Cellulose Acetate Butyrate |
3.60 |
5.00 |
| CP - Cellulose Proprionate |
3.70 |
4.10 |
| CPVC - Chlorinated Polyvinyl Chloride |
4.00 |
7.00 |
| ECTFE - Ethylene Chlorotrifluoroethylene |
5.00 |
5.00 |
| EVOH - Ethylene Vinyl Alcohol |
1.00 |
8.00 |
| HDPE - High Density Polyethylene |
15.00 |
15.00 |
| HIPS - High Impact Polystyrene Flame Retardant V0 |
1.00 |
2.10 |
| LCP - Liquid Crystal Polymer |
1.00 |
3.00 |
| LCP Carbon Fiber-reinforced |
1.00 |
1.00 |
| LCP Glass Fiber-reinforced |
1.00 |
3.00 |
| LCP Mineral-filled |
2.00 |
4.00 |
| LDPE - Low Density Polyethylene |
13.00 |
17.50 |
| LLDPE - Linear Low Density Polyethylene |
3.00 |
16.00 |
| MABS - Transparent Acrylonitrile Butadiene Styrene |
3.90 |
4.10 |
| PA 11 - (Polyamide 11) 30% Glass fiber reinforced |
3.00 |
4.00 |
| PA 11, Flexible |
30.00 |
49.00 |
| PA 11, Rigid |
5.00 |
10.00 |
| PA 12 (Polyamide 12), Conductive |
24.00 |
24.00 |
| PA 12, Fiber-reinforced |
5.00 |
42.00 |
| PA 12, Flexible |
25.00 |
26.00 |
| PA 12, Glass Filled |
5.00 |
6.00 |
| PA 12, Rigid |
5.00 |
15.00 |
| PA 6 - Polyamide 6 |
3.40 |
140.00 |
| PA 66 - Polyamide 6-6 |
3.40 |
30.00 |
| PA 66, 30% Glass Fiber |
3.00 |
3.00 |
| Polyamide semi-aromatic |
6.00 |
8.00 |
| PAI - Polyamide-Imide 30% Glass Fiber |
6.00 |
7.00 |
| PAI, Low Friction |
7.00 |
9.00 |
| PAN - Polyacrylonitrile |
3.00 |
4.00 |
| PAR - Polyarylate |
6.00 |
8.00 |
| PBT - Polybutylene Terephthalate |
3.50 |
9.00 |
| PBT, 30% Glass Fiber |
2.00 |
3.00 |
| PC (Polycarbonate) 20-40% Glass Fiber |
2.00 |
4.00 |
| PC (Polycarbonate) 20-40% Glass Fiber Flame Retardant |
2.00 |
4.00 |
| PC - Polycarbonate, high heat |
6.00 |
7.00 |
| PC/PBT Blend - Polycarbonate/Polybutylene Terephthalate Blend |
4.40 |
4.50 |
| PC/PBT blend, Glass Filled |
1.300 |
1.590 |
| PE - Polyethylene 30% Glass Fiber |
1.50 |
2.50 |
| PEEK - Polyetheretherketone |
5.00 |
5.00 |
| PEEK 30% Carbon Fiber-reinforced |
1.00 |
3.00 |
| PEEK 30% Glass Fiber-reinforced |
2.00 |
3.00 |
| PEI - Polyetherimide |
6.80 |
7.20 |
| PEI, 30% Glass Fiber-reinforced |
7.20 |
3.00 |
| PEI, Mineral Filled |
6.00 |
6.00 |
| PEKK (Polyetherketoneketone), Low Cristallinity Grade |
3.00 |
8.00 |
| PESU - Polyethersulfone |
1.90 |
6.70 |
| PESU 10-30% glass fiber |
2.00 |
6.00 |
| PET - Polyethylene Terephthalate |
3.80 |
3.80 |
| PET, 30% Glass Fiber-reinforced |
2.00 |
7.00 |
| PET, 30/35% Glass Fiber-reinforced, Impact Modified |
6.00 |
6.00 |
| PETG - Polyethylene Terephthalate Glycol |
3.90 |
4.10 |
| PI - Polyimide |
4.00 |
10.00 |
| PMMA - Polymethylmethacrylate/Acrylic |
2.00 |
10.00 |
| PMMA (Acrylic) High Heat |
2.00 |
10.00 |
| PMMA (Acrylic) Impact Modified |
3.80 |
5.00 |
| PMP - Polymethylpentene 30% Glass Fiber-reinforced |
2.00 |
3.00 |
| POM - Polyoxymethylene (Acetal) |
8.00 |
23.00 |
| POM (Acetal) Impact Modified |
10.00 |
15.00 |
| PP - Polypropylene 10-20% Glass Fiber |
3.00 |
4.00 |
| PP, 10-40% Mineral Filled |
2.00 |
3.00 |
| PP (Polypropylene) Copolymer |
6.00 |
250.00 |
| PPA - Polyphthalamide |
6.00 |
6.00 |
| PPE - Polyphenylene Ether |
2.00 |
7.00 |
| PPE, 30% Glass Fiber-reinforced |
3.00 |
3.00 |
| PPE, Flame Retardant |
2.00 |
7.00 |
| PPE, Impact Modified |
30.00 |
30.00 |
| PPS - Polyphenylene Sulfide |
1.00 |
4.00
|
| PPS, 20-30% Glass Fiber-reinforced |
1.00 |
2.00
|
| PPS, 40% Glass Fiber-reinforced
|
1.00 |
2.00 |
| PPS, Conductive
|
0.50 |
3.00
|
| PPS, Glass fiber & Mineral-filled |
1.00 |
3.000
|
| PPSU - Polyphenylene Sulfone
|
7.20 |
7.20
|
| PS (Polystyrene) Crystal |
1.00 |
4.00
|
| PS, High Heat |
1.00 |
4.00
|
| PSU - Polysulfone
|
5.70 |
6.00
|
| PSU, 30% Glass finer-reinforced
|
2.00 |
3.00
|
| PSU Mineral Filled
|
2.00 |
5.00 |
| PVC (Polyvinyl Chloride), 20% Glass Fiber-reinforced
|
2.00 |
5.00 |
| PVC Rigid
|
5.00 |
6.00
|
| PVDF - Polyvinylidene Fluoride
|
2.00 |
16.00
|
| SAN - Styrene Acrylonitrile |
2.00 |
5.00 |
| SAN, 20% Glass Fiber-reinforced
|
1.00 |
2.00 |
| SMA - Styrene Maleic Anhydride 20% Glass Fiber-reinforced
z |
2.00 |
3.00 |
| SMA, Flame Retardant V0
|
2.00 |
2.00
|