Understanding Micro-Mechanical Properties of Your Samples Using the Linkam Modular Force Stage (MFS)
November 19, 2020
In this free webinar, representatives from The McCrone Group and Linkam Scientific present an overview of the modular force testing system. Gain a better understanding of microscopic and thermo-mechanical properties on a wide variety of samples and applications.
Charles Zona (CZ): Good afternoon, and welcome to another McCrone Group webinar. My name is Charles Zona, and today we welcome Glenn Miller from McCrone Microscopes & Accessories along with Robert Gurney of Linkam Scientific Instruments. Glenn and Robert are going to talk to us today about Linkam’s Modular Force Stage. But before we get started, I would like to give you a bit of Glenn’s and Robert’s backgrounds.
Glenn joined the McCrone team in 2018 and provides client training in scanning electron and polarized light microscopes along with thermal microscopy applications and advanced sample preparation techniques Glenn travels the United States installing microscopy systems for customers, including Linkam thermal stages and benchtop scanning electron microscopes, and also provides client training on these advanced instruments.
Robert leads Linkam’s marketing department and also helps develop scientific applications across a variety of research fields and industries using Linkam instruments.
Today’s webinar is a little bit different in that it is recording, and not taking place live. However, you can still ask questions by typing them into the questions field. We will answer all of your questions individually in the coming days. This webinar is being recorded and will be available on The McCrone Group website under the Resources tab. And now I will hand the program over to Glenn and Robert.
Glenn Miller (GM): Thanks, Chuck. Hello everyone, and welcome to today’s webinar about the new Linkam Modular Force Stage. As Chuck mentioned, I will be presenting alongside Robert Gurney from Linkam Scientific. We’re happy to be an authorized dealer for Linkam, provide support for their stages, and furthermore, have the ability to share information with our clients about their exciting new instruments like the MFS. The Modular Force Stage is a continuation of Linkam’s previous tensile stage—the TST350, except it is different in that the majority of the components that make up this new stage are modular; this meaning that each of these features can be exchanged and the stage can be customized depending on your application type.
The exchangeable features are: The grips. For example, there are standard grips, serrated grips, or three-point bend grips. There are different force beams; there are as low as two newton beams and as high as 600 newton beams. There are multiple heaters that you can swap in and out, including a 350°C heater, an ambient base, and a dish for holding liquids. There are different accessory port options at the front of the stage, including an insert for electrical connections to your sample. Finally, there are different lids that you can use on top of this stage based on your sample, from a wider window than standard to attaching humidity ports on the top to control the relative humidity inside of the chamber.
With this stage, you can conduct force testing not only in the tensile direction, which is stretching the sample, but also in the compression direction. You can additionally purchase a FLIR camera system with the Modular Force Stage and take high-quality images of your sample, creating videos of your trials, and furthermore, correlating the thermal data that you capture along with the imagery. During these tensile trials you can control several different parameters, including the jaw speed, the distance moved, and the force applied to the sample.
This stage also comes equipped with a high-resolution encoder to ensure that measurement of the changes in the length is extremely precise.
Overall, this stage records incredibly precise movement, and force application from the jaws. The maximum travel of the jaws is 85 mm in total with a speed range during each ramp of 0.1 to 5,000 micron/second, depending on the beam and the force applied to the ramp.
There are several different movement modes that you can apply during each ramp, including a step movement, which is a particular length at a particular velocity; a velocity movement, which is simply opening or closing the jaws at a particular velocity; tensile and compressive cycling, which is repeatedly opening and closing the jaws for a particular length and velocity in a cycle; as well as a controlled force movement, which is applying a particular force to the jaws in either direction.
The resolution of the distance of the jaws is 1 micron, and the force resolution ranges from 10-2 newton to 10-5 newton, depending on the force beam that you have inserted in the stage, which range from 2 newton to 600 newton.
The Modular Force Stage is very easy to use with either a transmitted or reflected light microscope. It has also been used in the past with FTIR microscopes, as well as inside of glove boxes for small angle X-ray experiments. This stage can simply be placed on top of an existing microscope stage, or if your microscope has the ability to remove the stage, it can be mounted using stage clamps onto the dovetail of the microscope.
On the MFS, there are windows on the top and bottom of the stage, as well as an aperture through the heater block to allow for transmitted observation of the sample. Please be aware that there are working distance requirements for both the top and bottom lids in order to focus your sample, so your objective in use and/or condenser must conform to this. For the top lid, there’s a 50 mm window for larger samples, and if necessary, there’s a 16 mm window with a shorter working distance requirement.
As mentioned previously, a FLIR camera can be paired with the system mounted onto a microscope and capture imagery that is able to be correlated with the thermal data that is recorded during each ramp. This is the only camera system currently available to automatically intertwine imagery and thermal data. With other camera systems, you will have to do this manually.
Linkam also offers a microscope dedicated to capturing images and videos using the thermal stage, fittingly called the Linkam Imaging Station. This microscope uses only one objective at a time and has no eyepieces, but it adequately gets the job done for imaging specimens.
The software that controls the Modular Force Stage is Link core software. This software is controlled via a Windows 10 (or 7) 64-bit desktop computer. With this software, you have the ability to control and record your temperature, the distance the jaws travel, the force applied to the sample, as well as the time each trial lasts. This software, when combined with the FLIR camera system, can take images during your ramps and profiles and create full resolution movies with correlated force, distance, and temperature data. This is extremely helpful for going back after your ramps have finished and pinpointing particular events that occur within your sample visually to the data that is collected. The software has the ability to create one to 100 different ramps per profile, and each profile can be saved to your user interface for use at a later time. When imaging, you can also calibrate the microscope’s objective that is in use to apply a scale bar to the images and videos.
Now to help explore into the application aspects of the Modular Force Stage, Robert Gurney from Linkam Scientific.
Robert Gurney (RG): Hello. Thank you, Glenn, very much for the introduction. As you say, we have a really great working relationship between Linkam and McCrone, and we’re really happy to be able to work with companies like McCrone and others around the world to keep you informed about our products and the applications that they can be used for. So thank you to everyone for watching.
I think the MFS here is an excellent tool for mechanical testing, and has many, many possibilities and different configurations to enable you to do all sorts of different mechanical tests. We’re going to expand a bit on Glenn’s introduction and give a few examples of types of mechanical testing and the applications that you could use a device like this for.
Let me start by telling you about some of the resources we have available for you to learn more about the MFS mechanical testing with this kind of device. If you go to our website into the MFS page, you’ll find a lot of application notes and research articles, and other articles and information on what some researchers have been able to do with the MFS and its predecessor, the TST, and hopefully these are all really interesting resources for you.
To give you a little bit of background about myself: I’m Linkam’s applications specialist. I’ve been with Linkam for a bit over a year, and my experience is as a scientific researcher, and my PhD is in mechanical testing of polymers. I also did a bit on optoelectronics and photovoltaics, and now that’s expanded to cover all sorts of different microscopy techniques and thermal analysis techniques, but hopefully, I can give you a little insight into my view and what’s possible with mechanical testing.
As I said, there are so many possibilities in the mechanical testing, which I’m sure you know. Here are just a couple of the possibilities of the type of thing you can measure with a mechanical testing device—anything from tensile strength to fracture modes, and analysis, modulus, and elasticity of materials. You can look at lifetime analysis, and fatigue analysis, and that’s all in addition to being able to observe what’s happening through microscopy or a number of other techniques, which we’ll talk about a little bit more with the MFS.
So mechanical testing and these types of analyses that I just mentioned are applicable in all sorts of different research fields. I’ve listed a couple of them here—anything from biomaterials, polymers, pharmaceutical compounds, to flexible electronics and food—there are all sorts of uses for this type of testing. To accommodate this very wide range of applications and different materials that can be used for this type of testing, there are a lot of different testing protocols and testing procedures that can be used with a device like the MFS. Usually, that involves perhaps a different style of grip, and also different testing protocols themselves, which we’ll go into a bit more.
Here’s just an overview of some of those modules that are available, ranging from the grips as you see on the right. Here we have all sorts of different grips for tensile testing, compression testing, for three-point bending, and probing a liquid cell with electrical connections; different window types that all sorts of different modular options—and these are also always expanding. We’re very happy to talk with you about customizing these, or even starting from scratch for new grips or different types of modules for different applications.
I’m just going to discuss a couple of different types of mechanical testing procedures and go through examples of each of them on this page.
We’ll start with the tensile strain analysis, often leading to tensile failure or fracture. This is a very standard test in which the sample is held between two parallel grips, as you can see in the photograph here of the MFS. The sample is then extended by opening the grips, separating the distance between the grips while the force is measured as a function of the distance between these grips. A quite common ending of this experiment, as I’ve said, is the failure of the sample. The graph on the top here shows typical output of this type of test, using the Link software, where you see the force gradually increase with extension until such point as the sample fails and the force drops to zero.
This is a pretty common type of graph that you get from this kind of tensile experiment, and there are a lot of ways to look in more detail at typical or specific aspects of this graph. The first thing that you need to do, and it is pretty standard to make it a little bit easier to look across different sample sizes or discrepancies between samples, would be to use stress and strain rather than force and distance, or force and extension. You can do that by taking stress…by looking at force F over area as the cross-sectional area of the sample A, and strain is extension here d over the initial sample length l0.
So let’s talk a little bit about the curve that you get and how you can break that down into its more representative parts, which relates to sample behaviors. So here, let’s look at the blue curve where I’ve taken the idea of this stress-strain curve and enhance certain features so we can talk about them a little bit easier. So the first one to look at is this initial period of stress and strain, or extension, where you see a linear stress-strain relationship, or elastic relationship, where the material follows Hooke’s Law. You would find that if you were to reverse the tensile measurement and start compression back to the initial sample length, it should follow the same line; there shouldn’t be any change there, that is. So if you keep extending, you get to a yield point, σ (sigma) yield, which represents the point at which the elastic behavior, or the behavior following Hooke’s Law, ends, and the sample is usually irreversibly damaged and is starting its yielding or failure mode. You then find, in certain polymer samples, that you have a period of softening, or more commonly, hardening, which we can link to a couple of examples of this in literature; it gets a little bit more complicated into polymer mechanics.
During this whole procedure you see necking where the sample stretches out like shown in this little cartoon above, until such point, as we mentioned before, the sample fractures or fails and the stress drops to zero. And just before that point is usually where you measure the maximum, or ultimate, tensile strength from. And then you can go a little bit further. There are things you can do, such as measure the Young’s modulus, which is the slope of the initial elastic parts of the curve. You can also look at the area underneath to look for values of toughness, and generally, you can look at this and see all sorts of things about elasticity, plasticity, strength, toughness, failure, and get a good idea about how the material behaves just by looking at this curve. One final part to add on this, is that you can see the second curve—this red curve here—and this is just to give you an example what might happen if you were to heat the sample up. As you well know, Linkam specializes in temperature control devices and stages, and chambers for other microscopy, and spectral speed techniques, so of course we do a temperature control. We actually have a couple of temperature control module options available for the MFS. What you might see if you were to warm up a sample, is it will have a lower modulus, so a lower slope, initial slope, and a bit more extension, and maybe a similar fracture. That’s just an example of what you might be able to do by heating up your sample and seeing what happens.
I have one more example for you of tensile strain leading to fracture or failure, and this is one example of how you can get a lot of extra information or combine the information from the graph with what you get from your microscope or spectroscopic technique. In this case, we’re looking at the sample under a microscope. This is a sample of some kind of plastic packaging, and as I’m speaking, you can see the graph and video synchronously moving, and you can see what happens as you extend the distance between the grips, and finally the sample fails and breaks. And it looks fairly similar to the curves we’ve seen before. I think you can identify these points—the modulus, and you can just about see a yield point, and then you can see the failure.
So let’s move on to tensile cycling, or hysteresis. This is a test that you can do with the same setup. So using the same type of grips, the same sample, in this case, obviously sort of a polymeric rubber sample, and what you would do here is, rather than simply extending, you would extend at a set velocity and distance…until you reach a distance, I should say. When you get to that distance, you reverse the direction of the movement of the jaws back to the original position. This is shown in the top graph here, where you see extension in the blue curve sort of going up and down as you extend and go back to the original position and back again. You can see a lot of other things on this graph; this is one of the graphs you see in Link, just to show what is happening during a live experiment, or what has happened during a live experiment.
You see the force, as well, in yellow. You see the temperature sort of slightly increasing in red, and the purple line across the middle is representing images—each one of these little dots— they’re all joined together because a lot of them are representing a still image which can be stitched together to a video as you saw in the last slide. This then turns into a force extension curve, below in yellow, where you see that the hysteresis cycle and then as before you can look a little bit more in detail at what that means.
As we said, usually, if you were to turn around while you’re in the elastic region, you would see…it should follow the same curve. In reality, that doesn’t often happen. You usually lose a little bit of energy somewhere, or it may be that you’ve passed the yield point, which is the case in this graph here. And you do see a little bit of hysteresis and lost energy here, and another example of what might happen if you were to heat the sample up and repeat this experiment here.
So I showed you an example of what you might do for a tensile test, averse of a polymeric or a rubber-like sample. Here’s a different example using a three-point bending test. You can see in the photo on the bottom left we have special grips for this with three points, which you can press the sample and bend or break the sample in that way. This can be used for lots of different products from sort of structural beams or small structural beams like this, to food samples that can be broken, or tablets which can be crushed or broken. In this experiment you rest the sample between grips, and you set the direction of movement to move the grips back towards each other. And what you can see in the graph on the top left, if you look at the yellow curve you see the force exerted by the sample resisting, and the three points bending, and then eventually it breaks and the force returns to zero. Again, you can see the purple dots on this graph showing where an image has been captured.
So let’s move on to a couple of application examples. Here we have a publication from Imperial College, London, where they used firstly the TST and then the MFS system to test the mechanical properties of a fibrous composite material which consists of a base polymer matrix—a PVA, to which they added varying fractions of one-dimensional nanomaterials, which, namely double-walled nanotubes, that you can see in figure A. They created these fibers from this composite through a process called wet coagulation spinning, where they draw out material from a coagulation bath. This allows some control over the alignment of the nanotubes in the polymer and the polymer chains themselves, which can influence the properties.
So looking a bit more closely at this graph, you can see they show the results of the tensile testing they’ve performed on these fibers. What they show is that they found that the fibers are extremely strong, with tensile strength on the order of gigapascals. They looked at the various compositions with different amounts of the nanomaterials, and they found an optimum through refining this blend ratio, as you can see in the graph, here. They found as you start to add nanotubes the modulus and stiffness increase, but after a certain point you reach and then pass a maximum value for strength here. You can see they cut up the graphs right at the failure point, which is where, as we’ve seen previously, they would fail and break—the stress falls to zero.
Furthermore, and very interestingly, and a big reason for the importance of this paper, is that they found that using a process called evaporation induced self-assembly, which is basically where they added a little drop of water to the damaged fibers and then heated them, through this process, they saw they were able to heal a fractured fiber and recover quite a large amount of the original strength, which is quite exciting. It has implications for a lot of applications wherever self-healing composites could be used—from building to biomaterials to all sorts of different packaging fibers and protective materials. I will provide you a link to this paper; it’s an open source paper.
We also have worked with several members of this group, in particular Hanna Leese, who has since moved on to the University of Bath working on similar types of materials, who we’ve done a case study with her on her new work at Bath which is really interesting work, and it’s up on our website for you to download.
Here’s another example. In this case, the researchers are looking at the durability of adhesive coatings, which are used for things like semiconductor, and protective coatings, or flexible electronics, or bioelectronics. This work is from a group in Lausanne; we actually wrote an application note on this with them, so look out for that on the MFS page of our website. Here they tested the film under uniaxial strain, in what they call a fragmentation test method. They’re interested in the crack density rather than the stress of the material, which you can see through the insert images here, and also what they’ve plotted on the main graph. They essentially counted the number of cracks in a certain area, and the visible area under the microscope, and they saw that this number increased as the strain increased, up to a certain point which is around eight percent as shown on the graph here, where after the number of cracks stabilizes, it was saturated. And they also saw signs of delamination which occurred at different strains, which you can see from the lines across the sample and the figure on the right. And just to know that they colored the main images green to make it easier to see the cracks. In the paper they go on to apply this theory to define different stages of strain-based fragmentation for various types of coatings in this field, and this will be a useful analysis and theory for future analysis and comparison of coatings like this, and failure of coatings like this.
So let me give you one final example before I hand you back to Glenn. This paper here is on biomaterials, in particular bones, but in general I think they have a great way of presenting stress-strain data to show how mechanical testing procedures can be used to classify, and even predict, trends in microscopic—or let’s say real world—behavior, and depending on the results of tensile tests or other mechanical tests. As I said, this one here is on bones, strength of bones, but it could equally be for nanocomposite fibers, or reinforced concrete beams, or all sorts of different materials and their mechanical behavior.
So this paper is from a group in Hamburg who look at the mechanical properties of bones from three different sample groups. They take a femur bone sample firstly from healthy young individuals, and the second group is those with osteoporosis, and the third was treated with biophosphonate (BP), which is a treatment for osteoporosis.
For the test, they subjected the bone samples to trauma in the form of low or high energy induced fracture using three-point bending apparatus. You can see they’ve plotted stress versus strain here, and the curve follows a fairly typical progression with increasing stress until failure in all cases. And on the right—the bottom right, these three graphs show they’ve plotted the average modulus yield stress and maximum bending stress, which can all be calculated from the stress-strain curve.
And all of these graphs are a trend where BP improves the strength of osteoporosis-affected bones, but not quite as much as the original bone. The main graph here actually shows the average or standard deviation in stress-strain, from which they’re able to identify regions as shown on the graph associated with each of these three groups.
Okay, before I hand you back to Glenn, let me just point you in the direction of the MFS applications page on our website. You can follow the link here, where you can find application notes and links to research papers and other articles—all of the stuff I’ve mentioned today and more—so please do check it out. You can check out the brochure, as well.
- Inorganic Nanotube Mesophases Enable Strong Self-Healing Fibers
- Fragmentation Test Method for Adhesion Analysis of Coatings In Situ in a Microscope
- Intrinsic mechanical behavior of femoral cortical bone in young, osteoporotic and bisphosphonatetreated individuals in low- and high energy fracture conditions
And that’s all from me. Over to you, Glenn.
GM: Thank you very much, Robert. Now I’m going to go through some videos taken of the Modular Force Stage to show you what the anatomy of the stage looks like, as well as what imagery using the FLIR camera and software looks like.
So this first video that you can see on the slide is a macro view of the stage with a rubber band clamped down as the sample. I ran this for roughly a 13,000 micron cycle stretch, stretching it back and forth to show the elasticity of this rubber band.
Now we have a micro view of the rubber band with a 2.1 mm scale bar at the top left of the image. This goes through the same cycle as in the first video, but we’re able to watch it very closely, and even closer, if we desired. On the right hand side you can see the data on this ramp. Temperature is on the upper left y-axis and is ambient throughout the trial. Force is on the close right y-axis, and you can see it consistently increases and decreases through the trials. Extension is on the far right y-axis, and you can see it also consistently increases and decreases through these cycles, since we extended and retracted the same amount. On this upper graph, the purple line that’s going diagonally through the center is a data point for every image that was captured through this trial. Below this is a graph representing the force applied with respect to the length of extension. This has several lines back and forth due to the cycling, but shows that the amount of force applied is relatively linear based on the amount of extension.
On this slide, we have the surface of a band-aid stretching through a similar cycle as the rubber band, but only 3,500 micron back and forth. The extension and temperature fluctuations are similar in this experiment, but as you can see in the upper and lower force graphs, as you continuously extend and retract this band-aid, it requires less force to make the same extension over time. On the upper graph, the force peaks consistently decrease, and on the lower graph, there is a large amount of force for the first cycle and then it slowly drops off more and more as the cycles continue.
And for our final example, we did a pill crush in between the two jaws. On the left hand side you can see that we have the pill positioned horizontally in between the jaws, testing the compression force until failure in this direction. We set the jaws to close at 2 microns per second until failure, and then manually halted the experiment once we saw that the pill was crushed. You can see on the graph to the right that it took roughly 200 seconds and a force of 130 newtons to achieve failure, once the force jolts back to 70 newtons.
We’d like to thank you all for attending this webinar. As mentioned at the beginning, we will be answering any of the questions that you might have had during this webinar in the coming days. Resources and additional information can be found at the links below mine and Robert’s contact information. Please feel free to reach out, and have a great day.
CZ: Okay…thank you again for attending today’s webinar. If you have any questions, please go ahead and type them into the questions field, and Glenn and Robert will reach out in the next day or so to answer all of your questions. So we’ll leave the webinar open for a little while here, so you can type in any questions you might have.
I’d like to thank Glenn and Robert for doing this presentation, and a big thanks to all of you who tuned in today. We really appreciate your time. And please check out our webinars page for upcoming McCrone Group webinars. Thank you.