Monday 22 June 2020

My Polymer Material Selection Online Course (Update #1)


In this blog post, I give you an update about my new online training course “polymer material selection”. 

What is my motivation for teaching such a topic? 

It is quite simple: failures arising from incorrect material selection and grade selection are persisting problems in different industries. 

There are almost 100 generic “families” of plastics and 1,000 sub-generic plastic types available at over 500 suppliers. 

How to know which is the optimal for your part? 

The end users are responsible to select the right polymer for the right purpose. 

 In this course, I will show you how to select polymers in a systematic way by using my polymer selection funnel method. 

We will go over the entire selection process, from how to establish part requirements, gather material data, and rank different polymers all the way to how to select a vendor after selecting the polymer. 

In this course we will cover: 
-How to prevent plastic part failure 
-How to outline product requirements 
-How to define material selection factors
-How to search for proper material data 
-How to create a decision matrix and weighting different polymers 
-How to set up prototype and part testing 
-How to select the optimal polymer material 
-How to select the optimal material vendor 

In a few hours, you will learn everything you need to select the optimal polymer material for your project, save thousands by preventing part failure, and will have fun in the process. 

Stay tuned – launch date is July 1st.

Thank you for reading!

Greetings,
Herwig Juster

If you liked this post, please share and like!
New to my Find Out About Plastics Blog – check out the start here section

Monday 15 June 2020

Design Properties for Engineers: Flexural Properties of High Performance Polymers

In this post we compare the flexural properties of 12 unfilled high performance polymers.

In the standard ISO 178, a method for determining the flexural properties of rigid and semi-rigid plastics under defined conditions is described. A bar-shaped test specimen will be placed on both ends over a block and a force is placed in the middle of the specimen with a constant speed. In this way, stress and strain behavior for bending can be estimated. This is similar to the tensile properties, however for the load case of bending.

In the bending test, the resulting stresses and strains are located mainly on one side of the specimen. This leads to different stresses in the edges of the specimen. One side of the specimen will be bended, while the other side will be strained at the same time. The resulting stresses are distributed in a uniform way compared to the tensile test. Further, the maximal loads which are applied in the bending test can result in higher strength values compared to the strength values obtained from the tensile test.

In general, flexural test data can be used for indicating the behavior of the selected polymer in use.

Flexural properties of high performance polymers reflect the findings of the tensile test results. Ultrapolymers such as PEEK, PBI, and PAI, as well as LCP have excellent flexural properties. Fluoropolymers on the other hand, have a low bending strength.

Flexural properties of 12 unfilled high performance polymers


Further design property data of high performance polymers are listed on my start here page as well as on my SlideShare page.

Thank you for reading!
Till next time!
Herwig Juster

If you liked this post, please share and like!
New to my Find Out About Plastics Blog – check out the start here section

Literature:
https://www.polytron-gmbh.de/materialeigenschaften.aspx

Monday 8 June 2020

Design Properties for Engineers: Tensile Properties of High Performance Polymers

In this blog post we compare the tensile properties (tensile strength, elongation, and modulus) of unreinforced and reinforced high performance polymers, including high temperature comparisons (150°C and 200°C).

Tensile properties are suitable to characterize the mechanical behavior of plastics. They describe the relationship between applied force (expressed in stress) and the deformation resulting out of this force (expressed in elongation).

The most used test is the tensile test according ISO 527. In this test, tensile bars are stretched under constant velocity. As a result, tensile stress (MPa or N/mm2) and tensile elongation (%) are obtained. The ratio of stress to strain is called Young modulus.

Tensile properties of high performance polymers can vary depending which polymer type was tested. The table below shows the tensile properties of unreinforced high performance polymers.
Comparison of tensile modulus, tensile strength and tensile elongation of unreinforced high performance polymers

Thermoset polyimides such as PBI and PI show brittle and high strength behavior. On the other end of the polymer spectrum we have PTFE which has a low strength, however shows a high elongation capability. PEAKs and Polysulfones reflect the typical tough and hard behavior of thermoplastics. PAI has a high strength and can already be used as an unreinforced polymer for several applications. It is able to handle high forces and still has good elasticity properties. Overall, PAI has balanced mechanical properties.

PTFE has a tensile modulus between 750 and 800 MPa and a tensile strength of less than 50 MPa with an elongation of over 250%. All the other high performance polymers show higher tensile strength values, combined with tensile moduli of over 2 GPa. However, the elongation is much lower compared to PTFE. PBI is the counterpart to PTFE with a high tensile modulus of nearly 6 GPa and a elongation at break of only 3%.

PPS, PEEK, and PAI show balanced tensile properties and all three have high tensile moduli of 4 GPa. So far, we considered only unreinforced high performance polymers. Adding glass- or carbon fibers will change the tensile properties. Tensile strength is increasing and elongation is decreasing. In the table below we can see improvements in tensile strength of all polymer classes; however reinforced PTFE will not reach the same tensile strength level as the other high performance polymers, especially when they are reinforced too.
Comparison of tensile modulus, tensile strength and tensile elongation of reinforced high performance polymers

Influence of temperature 


The base strength of high performance polymers can be increased with reinforcement fillers. However with increasing temperature, mechanical values are decreasing. This is shown in the next chart below.

Amorphous and thermoset polymers behave differently compared to semi-crystalline polymers when exposed to temperature. Up to the melting point, amorphous and thermoset materials show a nearly linear strength curve. Semi-crystalline polymers have a step-curve behavior. Before semi-crystalline polymers reach their continuous use temperature (CUT), mechanical properties have already decreased. Mechanical performance can change within few temperature differences. This behavior is clearly shown in the chart below: PAI, PBI and PI show at 200°C still good mechanical properties, and even as good as engineering polymers at room temperature. The tensile strength of PPS and PEEK has reduced significantly. PEEK has a tensile modulus of 3 GPa at 150°C. Increasing the temperature up to 200°C results in a decrease of under 1 GPa. PAI, PBI and PI have still high moduli values at 200°C and this reinforces the need of selecting properly polymers when temperatures are high.
Tensile modulus of high performance polymers at 150°C and 200°C

I hope you found the tensile property data of  unreinforced and reinforced high performance polymers, including high temperature comparisons (150°C and 200°C) useful and they can be helpful for you next part design or specification project.

Further design property data of high performance polymers are listed on my start here page.

Thank you for reading!
Till next time!
Herwig Juster

If you liked this post, please share and like!
New to my Find Out About Plastics Blog – check out the start here section

Literature:
https://www.polytron-gmbh.de/materialeigenschaften.aspx