Impact of Temperature on Mechanical Properties
The impact behavior of plastic materials is strongly dependent upon the temperature.
- At high temperatures, materials are more ductile and have high impact toughness.
- At low temperatures, some plastics that would be ductile at room temperature become brittle.
Brittleness is a general term indicating that a polymer absorbs relatively little energy during fracture i.e. it may simply mean that it breaks easily. While ductility of a material is its ability to deform under load.
What is ductile/brittle transition temperature (DBTT)? It is the transition temperature below which a ductile plastic specimen becomes brittle, i.e. when the ductile / brittle transition occurs - boundary between
brittle and ductile behavior.
This is usually not a specific temperature but rather a temperature spread over 10°C range.
The brittle-to-ductile transition is one of the
important thermal properties to consider in the selection of a material. It is essential for the
understanding of part failure processes (fatigue, overload, or environmental stress cracking) especially in parts used for structural applications, especially in low‐temperature conditions.
Ductile / Brittle Transition Temperature (DBTT) is expressed in °C.
It is equally important to understand that, on cooling of polymer, the ductile/brittle transition temperature may not necessarily correspond to the brittle/ductile transition temperature observed on heating of the polymer.
Check out more on Ductile / Brittle Transition Temperature
How to Measure Ductile / Brittle Transition Temperature
Standard to measure Ductile / Brittle Transition Temperature is ISO 6603-2 (multi-axial instrumented impact).
It specifies a test method for the determination of puncture impact properties of rigid plastics, in the form of flat specimens, using instruments for measuring force and deflection. It is applicable if a force-deflection or force-time diagram, recorded at nominally constant striker velocity, is necessary for detailed characterization of the impact behavior.
ISO 6603-1 can be used if it is sufficient to characterize the impact behavior of plastics by a threshold value of impact-failure energy based on many test specimens.
Also Read: Toughness of Polymers & Izod and Charpy Test Methods for Measurement
Factors Influencing Ductile-Brittle Transition
![Brittle Vs Ductile Fracture in Material]( "Brittle Vs Ductile Fracture in Material")
Brittle Vs Ductile Fracture in Material
(Source: Reliability Design of Mechanical Systems, Woo, Seongwoo)
An increase in temperature brings about changes in the state of the
amorphous polymers (e.g. polycarbonate (PC), general-purpose polystyrene (GPPS), polymethyl methacrylate (PMMA), polyvinyl chloride (PVC), acrylonitrile butadiene styrene (ABS)), and hence, brings changes in the tensile behavior of the polymer. As discussed above, at the lowest temperature, polymers are brittle. As the temperature increases they become more tough until they reach Ductile-Brittle Transition.
It is above this transition temperature that polymers become sufficiently ductile that they can exhibit necking. Still further increase in
temperature produce a rubber-like behavior that is displayed until mechanical strength breaks down.
Crystalline polymers (e.g. polyolefins, polyether ether ketone (PEEK), polyethylene terephthalate (PET), acetal (POM), etc.) follow the mechanical behavior of amorphous polymers at the low temperature. Hence, their ductile-brittle transition temperature is established by the amorphous content of the material.
Thus, the more crystalline is the material is, the less sensitive it is to the changes brought by the amorphous content.
Crystalline polymers show high strength & less ductility
than the same polymers in the amorphous state at the same temperature
Cross-linked polymers have the same range of mechanical properties displayed by amorphous polymers, so long as the crosslinking is light. As the crosslinking increases, the mechanical properties are modified such that at the extreme end of high crosslinking, the polymer is virtually insensitive to temperature changes.
There are many factors (to consider for designers!) that contribute to make a ductile polymer behave in a brittle manner. These include:
- Stress concentration & design features: Faster stressing, cyclic loading, triaxial tension etc. are some of the feature that tend to make ductile polymer more brittle.
- Polymer & compound features: Increase in crosslink density restricts molecule mobility and hence make polymer more likely to brittle. Change in proportion in copolymers and blends can lead to change in balance of properties and hence toughness may suffer. Plasticizers are used to increase
flexibility – however a decrease in plasticizer concentration (either deliberately or migration) reduces ductility. Hard particulate fibers used to reinforce the polymer may impair the toughness of composition & reduce the
elongation at break.
- Processing features: Melt processing to shape polymers may introduce several features which can promote embrittlement. E.g. Development of anisotropy by alignment of molecules or fibrous fillers; inhomogeneity giving a distribution of microstructure throughout the wall thickness of a product or residual stress caused by solidification from the melt during cooling.
- Environmental factors such as temperature: Decrease in temperature leads to less mobility and hence more brittle behavior of plastics. This transition is more marked in amorphous polymers near their Tg.
Other factors that influence the ductile-to-brittle transition include chemical contact, degradation, contamination, strain rate etc.
Polymer Grades with Good Ductility at Low Temperature
Ductile / Brittle Transition Temperature Values of 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 (°C) |
Max Value (°C) |
| ABS - Acrylonitrile Butadiene Styrene |
-25.00 |
-40.00 |
| ABS Flame Retardant |
-40.00 |
-20.00 |
| ABS High Heat |
-40.00 |
-20.00 |
| ABS High Impact |
-40.00 |
-20.00 |
| ASA/PVC Blend - Acrylonitrile Styrene Acrylate/Polyvinyl Chloride Blend |
0.00 |
8.00 |
| CA - Cellulose Acetate |
-30.00 |
-30.00 |
| ECTFE - Ethylene Chlorotrifluoroethylene |
-76.00 |
-76.00 |
| ETFE - Ethylene Tetrafluoroethylene |
-100.00 |
-100.00 |
| EVA - Ethylene Vinyl Acetate |
-69.00 |
-69.00 |
| FEP - Fluorinated Ethylene Propylene |
-150.00 |
-150.00 |
| HDPE - High Density Polyethylene |
-70.00 |
-70.00 |
| HIPS - High Impact Polystyrene |
-40.00 |
-20.00 |
| HIPS Flame Retardant V0 |
-40.00 |
-20.00 |
| Ionomer (Ethylene-Methyl Acrylate Copolymer) |
-110.00 |
-71.00 |
| LCP - Liquid Crystal Polymer |
-200.00 |
-50.00 |
| LCP Carbon Fiber-reinforced |
-200.00 |
-50.00 |
| LCP Glass Fiber-reinforced |
-200.00 |
-50.00 |
| LCP Mineral-filled |
-200.00 |
-50.00 |
| LDPE - Low Density Polyethylene |
-70.00 |
-70.00 |
| LLDPE - Linear Low Density Polyethylene |
-70.00 |
-70.00 |
| MABS - Transparent Acrylonitrile Butadiene Styrene |
-40.00 |
-40.00 |
| PA 66 - Polyamide 6-6 |
-80.00 |
-65.00 |
| PA 66, Impact Modified |
-105.00 |
-85.00 |
| PAI - Polyamide-Imide |
-196.00 |
-196.00 |
| PAR - Polyarylate |
-100.00 |
-95.00 |
| PBT - Polybutylene Terephthalate |
-40.00 |
-40.00 |
| PCTFE - Polymonochlorotrifluoroethylene |
-250.00 |
-250.00 |
| PE - Polyethylene 30% Glass Fiber |
-110.00 |
-110.00 |
| PEEK - Polyetheretherketone |
-65.00 |
-60.00 |
| PEEK 30% Carbon Fiber-reinforced |
-65.00 |
-65.00 |
| PEEK 30% Glass Fiber-reinforced |
-65.00 |
-70.00 |
| PESU - Polyethersulfone |
-98.00 |
-101.00 |
| PET - Polyethylene Terephthalate |
-40.00 |
-40.00 |
| PETG - Polyethylene Terephthalate Glycol |
-40.00 |
-40.00 |
| PFA - Perfluoroalkoxy |
-150.00 |
-150.00 |
| POM - Polyoxymethylene (Acetal) |
-40.00 |
-40.00 |
| POM (Acetal) Impact Modified |
-50.00 |
-40.00 |
| POM (Acetal) Low Friction |
-40.00 |
-40.00 |
| PP - Polypropylene 10-20% Glass Fiber |
-30.00 |
-5.00 |
| PP, 10-40% Mineral Filled |
-20.00 |
-5.00 |
| PP, 10-40% Talc Filled |
-20.00 |
-5.00 |
| PP, 30-40% Glass Fiber-reinforced |
-30.00 |
-5.00 |
| PP (Polypropylene) Copolymer |
-20.00 |
-10.00 |
| PP (Polypropylene) Homopolymer |
-20.00 |
-10.00 |
| PP, Impact Modified |
-40.00 |
20.00 |
| PPE - Polyphenylene Ether |
-50.00 |
-40.00 |
| PS (Polystyrene) Crystal |
20.00 |
20.00
|
| PS, High Heat |
20.00 |
20.00
|
| PSU - Polysulfone
|
-100.00 |
-100.00
|
| PTFE - Polytetrafluoroethylene
|
-200.00 |
-200.00
|
| PVC (Polyvinyl Chloride), 20% Glass Fiber-reinforced
|
-10.00 |
1.00
|
| PVC, Plasticized |
-40.00 |
-5.00
|
| PVC, Plasticized Filled
|
-40.00 |
-5.00
|
| PVC Rigid
|
-10.00 |
1.00 |
| PVDF - Polyvinylidene Fluoride
|
-62.00 |
-30.00
|
| SAN - Styrene Acrylonitrile |
20.00 |
20.00
|
| SAN, 20% Glass Fiber-reinforced
|
20.00 |
20.00
|
Related Read: Glass Transition Temperature in Plastics