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Impact Resistance - tips for plastic material selection

Either I am dumb or the Izod and Charpy values expressed on the datasheets are confusing, but I have never been able to utilize them in practise. Apart from the units being sometimes in J/m and sometimes in J/m2, the tests are conducted in circumstances that are not particularly realistic in terms of load case, product geometry, material orientation and temperature. I understand that the general purpose of the data is to help designers to compare different plastic grades, but in case of impact resistance I haven’t found them useful. If you have been able to make use of them in practise, please tell us how in the comments at the bottom of this page. I have instead opted to divide the plastic materials into three groups:

1 Brittle materials that should be avoided when risk of impacts is high

These are for instance amorphous grades, such as PS, PSU, SAN and PMMA (although it is used on ice-skating rink panels). They all share a lack of overall toughness. Lack of toughness is also a factor that reduces the impact resistance of some reinforced plastics. PPS+40GF, for instance, has very high modulus and therefore low toughness. If you knock the edge of the corresponding Plasticprop sample, you can hear a glassy sound. This indicates low impact strength. The same applies for polypropylene. PP-H (homopolymer) is stronger and stiffer than PP-C (copolymer), but its toughness and therefore impact resistance is smaller.

2 Impact resistant materials

Polycarbonate PC is the mother of all impact resistant plastics. However, its superior properties are not fully explained by high toughness. The molecule structure of PC is very firm and it requires a lot of energy to tear the chains apart. The high impact resistance of polycarbonate is utilized in many alloys like PC/ABS, PC/PBT and PC/PA. Here is an amusing video that illustrates PC impact resistance over PMMA:

ABS is also known for its impact resistance which remains good also in low temperatures. This is based on the small butadiene particles that absorb the impact energy. The same principle applies also for HI-PS and impact modified PP (PP+TPE-O). PPO was earlier quite common choice for TV housing. It is often used as an example of good impact resistance, but my personal experience of the material is limited.

3 The materials in between the two

Practically all engineering plastics like PA, PBT and POM withstand impact relatively well. This again depends on toughness. If you can cause a permanent deformation of a material sample by bending it, the material is probably quite impact resistant.

Other material aspects to take into consideration

Reinforcement

Reinforcements are two-edged swords when it comes to impact resistance. Increased strength is a benefit but high stiffness reduces toughness. Being able to decode the Charpy-V or Izod values might help, but I suggest studying each case with a hammer.

The effect of temperature

Service temperature is an important factor in impact resistance. In elevated temperatures it tends to be higher (to a limit), but when it is lowered, plastic products tend to turn stiffer. As the modulus of the material is increased, some toughness is lost. Amorphous plastics do this gradually but semi-crystalline materials might turn from ductile to brittle very suddenly as the temperature goes below their Tg. A water bucket made of PP (Tg app -10°C), for example, might easily break on a cold winter day while a HD-PE bucket (Tg app. -90°C) is still ductile. Based on this, one might expect PA6 (Tg app. 50°C), for instance, to be brittle in room temperature, but it is not. It is not that simple, in other words; each plastic material has its own characteristics. Finding a stress-strain-temperature curve for each material candidate is therefore helpful and Campusplastics database is worth researching: Type for an example "stress-strain PC" into the search-area to find diagrams available for different PC grades.

Impact fatigue

Resistance against fatigue applies to impacts as well. Some plastic products might withstand single shocks well, but fail with repeated impact, even with smaller energy level. My practical experience on such cases is limited, but my understanding is that amorphous materials are more sensitive to impact fatigue than semi-crystalline, as is the case with normal fatigue. More detailed information on the phenomenon can be found in this article by Dupont.

Geometry

How to increase impact resistance with geometry? Very often material selection is determined by multiple requirements. A compromise in material impact resistance does not necessarily mean loss of ductility for your product, however, while even the toughest material fails if the product is not properly designed. Tips how to increase impact resistance with mechanics/geometry can be found here.

 

This blog focuses on the hands-on design of injection molded plastic products. If it is something close
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Thank you for reading,

Markus Paloheimo, Managing Editor, plasticprop.com

  • Markus Paloheimo (Ms.Sc) is a Product Designer with two decades of experience in the field of functional consumer and industrial products. His specific area of expertise and source of enthusiasm is injection molded plastic products. Markus Paloheimo is in LinkedIn.

Comments

Tommy Tullos
I found your article very helpful, I am a student at Baton Rouge Community college and we are trying to develop a payload resistance when dropped from an near space environment with the aid of a small parachute. The problem I'm running into is the whole payload can weight no more than 1 pound. Is Styrofoam the best material for this project or do you have any ideas that can aid me in this project. Thanks
Markus Paloheimo
Hello Tommy, thanks for your feedback. It is a bit difficult to say without seeing the application, but some sort of a sandwich structure using Styrofoam sounds reasonable. Perhaps you use foam for constructing a bumber element on the spot that first hits the ground. That would absorb some of the energy.
Paul
Do you think stacking multiple sheets of a Polycarbonate will help increase its strength? for example adding 1/4" + 1/4" to make 0.5"
Markus Paloheimo
Paul, Sometimes a thick layer of plastic might have slightly foamy central area (due to process and cooling) and therefore it might be relatively weaker in correspondence to part with smaller wall thickness. But theroretically strength should be the same. Stiffness of the structure, however, is decreased unless you glue or rivet the two layers together.
Eric
I am trying to figure out out impact resistant 1/8" ABS is and if temperatures between 45 and 100 degrees would affect its durability in stopping pitched baseball at between 50 and 90 MPH.
Markus
Hello Eric, In Celcius that range would be from app 7C to 38C. ABS is very durable in low temperatures (far below that) but softens already in 80-100C. If the shield has proven to withstand the impacts close to room temperature, I would say that the risk is relatively low. It might be that the component can withstand the impacts better in 38 C than in room temperature. But isn't this quite easy to test in practise?
Mick Rodgers
Hi I am currently working on a project whereby I need to provide a see through barrier/guard with extremely high impact resistance. I am looking to shield working personnel from potential pipe joint failure. The 2" diameter pipes are carrying hydraulic fluid and are subject to working pressures of up to 10,000 Psi, the guard would be positioned approximately 3" away from the pipes. Any advice would help Mick
Markus
Hello Mick, I'd see polycarbonate quite ideal for this. It is transparent and offers the best impact resistance of all plastics. You should makes sure that the shield itself is not under continuous pressure (this goes with the fastening method as well, no bending, no tight screws). Chemicals are hazardous to PC, so it would be good to prevent people from touching the screen with dirty gloves etc. too much. Markus
Brian McLaughlin
Hello, We are currently producing a child's product that will be made of polypropylene # 5. We need to have the CSPC test it and one of the tests is a "drop test", which is dropping the product 10 times from a height of 4.5 feet. Will PP # 5 withstand this test and not break apart. Respectively, Brian McLaughlin
Markus
Brian, that depends very much on the weight of the product. Can you find a corresponding product and attach some weight on it... making it similar to your product? If you can then successfully drop it 50 times or from a height of 8 feet, you can be quite confident that the final product will survive the test. Markus
David Bourne
Hello, I'm an mechanical engineer (unfortunately with limited knowledge of plastics) working on a quality issue of cracked/fractured window cassettes. We use a product with 2,5mm PMMA sheet x 2 with a distance strut between to create a 19mm thick double glazed window cassette. I discovered that the window frames, on either side of the cassette, when screwed together create a continuous pressure on the cassette surface and I assume that this is the main reason behind the cracks they suffer? I guess that in a construction of this kind the frames on either side should bottom-out and the cassette ideally "float" between rubber seals? Would the same thing apply for SAN material in the same application? Any help you can offer is much appreciated / David
Wayne
In my opinion, part of the problem is that the theory of the test is wrong. The theory behind the Charpy impact test is that the energy consumed in breaking the material is measured and expressed as energy/area broken. For a tough material, energy is initially absorbed in deforming the material. Some is converted to heat and some is stored and available for release when the stress is removed. When the break occurs, the stress is relieved and some of the stored energy is released as mechanical motion and some as heat. The Charpy impact test attributes all this to energy consumed in breaking the material. When a value is given as energy/length, it is dimensionally incorrect if the above theory is applied. For the IZOD test, the depth of the break is always 1/8 inch and apparently omitted in reporting the result, so instead of reporting 12 ft-lb/in where inches is the width of the sample, it would be 96 ft-lb/sq in to reflect the area broken.
Markus
That is a good point and worth keeping in mind.. Thank you Wayne!
Markus
David Bourne, As PMMA, SAN is also an amorphous material and prone to stress-cracking. There is a high risk that the same phenomenon will occur with SAN...or actually any transparent plastic material. If possible, try to avoid the over-tightening situation.
Eric
Markus, You answered me about the impact resistance of 1/8th in. ABS with regard to temperature about a year ago. My project is moving along well and I understand your responses are not guarantees. But, I am trying to find test data or opinions that show the resistance of this with regard to a baseball or lacrosse ball thrown at up to 100 MPH or other comparable test data. Can you point me in the right direction? Thanks
Markus
Sorry Eric, I checked my database but did not find an article or study that would be a straight answer to your problem. If you are worried of performance in eleveated temperature, you could try PC/ABS. That does not increase cost significantly. Still, I would rather trust testing that datasheets on this.
Paul Tana
Nice article Markus Paloheimo. It has enabled me to make an intuitive decision as to the encapsulation of my device. I can't tell you what that device is as it is a company secret. Polycarbonate is a very strong thermoplastic polymer and has excellent properties for Mining and Oil & Gas environments. I am also exploring if Polyurea can be used to strengthen it more. Thanks for the information, it was a really good source... Kudos.
Humberto
Hi. Please help to choose I need to have a big area for LCD so material must be clear, but the problem is the unit will be inside a car, so having direct sunlight. in terms of strenght, best is to have Clear PC, but the problem is the aging of it, so PMMA is better because it dont get yelowish and is more scratch resistent and it can also be polished. but at same time is much less impact resistant. Is there any way to improve the impact resistance of PMMA. or are there an efective way to improve the scratch resistence to PC and also aging resistence? Thanks
Markus
Hello Humberto, PC screens are commonly used with a UV protective film. Have you studied those?
Azeem Ali(karachi pakistan)
hello, i have material problem with my Bulk Needle Hub component. i fix hub on syringe 5cc barrel due to low stiffness hub stretched.when i compare my hub with other one or ISO standard so,its size tapper same but due to stretched it gets lose please suggest high stiffness PP material to control fixing my component. waiting for your reply.
Muhammad Azeem Ali khan
Hi, Markus, please help me that, i am making my product in (PP 589 titan) material but due to low stiffness component stretched on conical fitting kindly suggest any PP material which has high stiff and Rockwell property.
Markus
Muhammed, how about adding some glass fibre in? Markus
Markus
Azeem, wouldn't some glass fill would do good to your case as well? Or can you go from PP to PA or PBT? This would give you higher modulus. PP homopolymer should have slightly higher modulus than PP copolymer.
Chel
Hi Markus, We have PA6 samples from 2 different suppliers... At normal temp, they both look good. But when we subject both to -15degC for 2 days, we did a hammer test. One is brittle, the other one just bend when we hammered it. We actually wanted the latter result. But weird that it is the same material yet they perform differently at low temp. Any thoughts why this happened? Thanks.
Markus
Hello Chel, The difference can sometimes be significant. It might be the softeners that are used. They have effect on the mechanical properties and therefore toughness of the material. Most likely, under the said temperature, the brittle sample is stiffer than the durable one. When changing from one supplier to another (wihtin the same grade) you should always make sure by testing that the outcome still fulfills the original requirements. Changing the material might have an effect on surface quality, colour/shine, straigthness and dimensions as well.
Andrew (Eindhoven, Netherlands)
We are using a Lexan 143R PC in a component (wall thickness 3mm) where it is required to survive the IK 10 (20 J) impact, but it shatters on the second hit! There is not much scope in changing the wall thickness, so I am looking for an alternative plastic with better impact resistance properties. I know PC is pretty much the "mother of all impact resistant plastics" but is there anything else we can try? Thanks.
Markus
Hello Andrew, Could it be the desing or process? Are there any sharp corners or could there be a weld-line on the stressed area? Without knowing the dimensions of the whole product 3 mm wall thickness sounds fairly high. But that being the reason for breakage, I don't think so. Perhaps you could try some other grade, but there is not really a reasonable substitute for PC, especially if the product is transparent. Markus
Anuj Sonthalia
Hi Markus, We have started manufacturing Airport trolley. We were a bit worried of the type of plastic we should use to make the front bumpers of the trolley. The trolley would be used in very hot temperature areas and also places with heavy snowfall. Could you please suggest the right plastic which can withstand the range of temperature and have a high impact resistant. We plan to fit it on to the tubular structure of the trolley using metal rivets. We were looking at option of PVC.
Markus
Hello Anuj, As a bumber, it has to be soft, right? What do you mean by "very hot temperature". Over 100°C? Typically TPE-O is used on car bumbers. If this is enough for automotive industry, could it be suitable for a trolley as well? Elevated temperature does not necessarily make the bumber any worse as a bumber as long as it does not get too soft and collapse under the impact. In low temperature some materials get brittle. That is worth checking. I recommend you try to find some more reference cases where a certain material has proven to serve well under similar circumstances. You can also do some practical tests yourself using a freezer or an oven. Perhaps LDPE, TPE-U, EVA...
Mark Hupertz
Hi Marcus We manufacture conveyor products and have designed a plastic housing that will replace a cast steel housing. However in underground coal mines they do not permit Aluminium or plastics unless they can pass the fire hazard test. Previously the standard was FRAS ( fire resistant and anti Static) However latest developments now focus on VOC and toxicity when it burns. Are there materials available for high impact or Impact modified plastics that are FRAS and least harmful when burning. Look forward to hearing from you.
Rob Savage
Hi Markus My question goes to the forming of parts in PC Can PC be injected into moulds and is there a limit to the thickness one could go to in a solid rod form.
Markus
Rob, You can buy PC as rod. Those are made by extrusion rather than injection molding. In injection molding I would consider 6-8m as an upper limit for PC, depending on case. Just google "polycarbonate rod" and you see what is available. Markus
Markus
Mark Hupertz, Sounds challenging. Please check this https://www.ensingerplastics.com/en/shapes/high-performance-plastics These materials are widely used in aviation industry due to their good fire resistance. The downside of these materials is their cost. There are more common plastic fire retandant grades available as well. I believe in your case the classification should be at least UL-94/V0. https://en.wikipedia.org/wiki/UL_94 Good luck, Markus
Joe Olivera
Hi Markus, I am starting the process of building a impact resistant music instrument case for air traveling. I was thinking in using ABS, is that the right choice? Would you recommend any other material? Thanks.
Markus
Joe, I don't see any reason why ABS would'n be the material in your case (and for your case). It is relatively cheap, has good impact strength and does not easily get brittle in low temperatures. Pleas bear in mind ABS sensitivity to stress cracking. Good luck with your product, Markus
Gary Flanagan
Hi Marcus, Your thoughts of replacing an extruded square length 4.0 metres long, 30mm external diameter with a 3mm internal wall section material: Black Polycarbonate Looking at replacing Polycarbonate with a Copolymer Polypropylene. Advantages/ Disadvantages Please??
Loei Badreddine
We are trying to use polycarbonate in lieu of plywood. I am trying to find out what thicknesses of ploycarbonate sheet I need that are equivalent to 1/2" and 3/4" plywood from impact resistance aspect. Thanks,
Markus
Gary, Did I get this right, you want to replace PC with PP? Advantages: Lower cost, less weight, better chemical resistance, better resistance against continuous stress, better against fatigue Disadvantages: Lower modulus and strength, lower impact strength (if the structure is tough, it might be OK), lower service temperature, difficult to glue or paint if needed. Hmmm...thats about it. Good luck, Markus
Markus
Hello Loei, Very difficult to say. Even though PC is very impact resistant, if you get a small crack on it, it starts spreading. Plywood does not do that since it is cross-laminated. So, when it comes to impact resistance, I don't think you can reach the level of plywood. But you might still reach the level that is sufficient for your purpose. Markus
Tarjei Neverlien
Hi. My company is looking to change some products from PC/ABS to pure PC because of dropping prices of PC. But so far we have found that the pure (10% glassfilled) PC materials we have tested are more brittle in cold climate testing (products for Nordic market). Is this a general rule? That adding ABS will give better impact properties in cold climates. I have some additional questions related to other challenges related to changing to pure PC (both PA6 to PC and PC/ABS to PC). For example 1. Use of regrind material, 2. Moulding parameters, 3. Design of Mould, .. etc It seems that your forum may offer some advice - do you have somewhere could I post such questions?
Markus
Tarjei, It is true that ABS has very good impact resistance in low temperatures and that is one of the most common reasons for compounding PC and ABS. When changing from semicrystallinen PA to amorphous PC you have to be especially careful with continuous stress leading to stress cracking. Especially if there may be some chemicals involved. You can send me email to markus@plasticprop.com. Markuks
Kristine Dayao
Hi. I am only a grade 11 student working on our invention project. I am looking for a material with high impact strength which can be used as a table top. Anyway, our proposal is an earthquake-proof table for school which can withstand falling objects. Do you think that polycarbonate can be used as a shield?
Markus
Kristine, Yes, if it needs to be transparent. If not, ABS would be cheaper option and still quite strong against impacts. If you want to hide under the table, I would see the metal legs as vital part of the construction. Good luck with the project! Markus
Jonny
Hello Markus. I´m really impressionate with this website. Congrats!! I´m working in a pair of bracket (right and left) that stands a LCD screen in their middle. This LCD screen must not be released after an impact test (about 5 kg at 20 km/h) towards its screen (it means that the brackets must not collapse). In short, between the screws that fasten LCD/bracket and the screws that fasten bracket/support, it is about 50 mm, and I´m designing them by reinforcing with many ribs in between them (parallel ribs). I´m planning to apply PC/ABS blend, but would like to know if there is so kind of reinforcement to increase this resistance to impact, just like increasing the elastic deformation, in order to delay the rupture as much as possible. And I don´t know if the ribs will help or disturb the elastic deformation, by making it brittle. What do you think?
Markus
Jonny, PC/ABS is very strong against impacts. There should be grades that are especially modified against impacts. You need to make sure that the component does not carry too much weight in order to avoid stress cracking. And please pay attention to the screw bosses as well. Parallel ribs do not necessarily make the frame much stiffer against bending. It is possible that you get a stress concentration on one of the ribs, but my hunch is that if you reach the level of deformation required for this, your screen is on the floor already. If the product is not very big, you get a pretty good picture of the difference by 3D-printing (SLS) the bracket with and without the ribs. Of course the material is not the same and there are no weld lines and such, but usually this type of comparison is very informative. BR, Markus

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