Tensile Test

If you’ve always wondered what a plastic component from a 3D printer can withstand, you’ve come to the right place. As part of the SmaP research project, we teamed up with the UTS Chair of Forming Technology and literally put our prints to the test (yes, well, maybe more like clamped).

The Attempt

The test we have carried out is the tensile test according to DIN EN ISO 527-1. This DIN standard contains the basic information about the exact execution of the tensile test for plastics.

The Sample

The specimen was dimensioned according to DIN EN ISO 527-2. This standard specifically defines the test conditions for molding and extrusion compounds. In our case, it is an extrusion compound, which is due to the manufacturing process (FDM 3D printers like the ones used extrude liquid plastic into an extrusion compound). Our specimen is a flat specimen of type 1A, this has a rectangular shape with so-called heads for clamping wedges. The width is 10 mm and a thickness of 5 mm.

Test Execution

3 different materials from 2 different printers were tested. 5 samples each were made. Samples of polylactide (PLA) and polyethylene terephthalate (PETG) were printed on one of our Prusa i3 MK3s printers. Furthermore, samples of onyx were produced on the Markforged MarkTwo. Onyx is a nylon with portions of carbon short fibers. For the test, a material sample in standardized form is inserted into a tensile testing machine. This machine stretches the specimen during the test until it breaks or elongation occurs without breakage (looks then like an elongated chewing gum). The specimen is stretched at a standardized speed (1 mm/min). The tensile testing machine continuously pulls the specimen apart during the test. The force that the specimen opposes this imposed strain is meanwhile recorded via the strain. The values in the evaluation can then be determined from the measured data. In the video below, you can see the experimental procedure and the tearing of a sample.

Results

The evaluation contains all essential information about the test and its boundary conditions, as well as a stress-strain diagram, the images of the specimens, and the data on material properties obtained from the test.

PLA

In the stress/strain diagrams of PLA, the range of elastic deformation can be seen in the range of about 0 – 1.8 %, which then stops abruptly when the tensile strength is reached, and changes to plastic deformation. From the area of plastic deformation, approximately between 1.8 and 2%, the quite pronounced part of the necking begins. The material still allows about 1.5% elongation until it finally breaks.

PETG

With PETG, the result cannot be reconstructed quite as nicely as with PLA. Sample PETG_P1, the upper outlier in the diagram, changes from the elastic to the plastic range at about 55 MPa, which then leads to necking at 60 MPa and ends in fracture of the sample at an elongation of 5.1%. The four other specimens behave similarly for the most part and also have only a small area of plastic deformation and pronounced area of necking. Compared to PLA, the elastic range of PETG is more pronounced.

Onyx

The onyx material also has a continuous transition from elastic to plastic deformation, although the region of elastic deformation is difficult to discern. Apparently, this ends at about between 8 and 10 MPa and then turns into a very pronounced part of plastic deformation, which subsequently leads to fracture with only slight necking.

Comparison

In this comparison, all evaluated specimens are summarized in a stress-strain diagram.

Here it can be seen that the specimens made of onyx (black) allow almost twice as much strain until fracture occurs, compared to the specimens made of PETG (red). Compared to the other two materials, the samples made of PLA allow even less elongation and are all already torn at an elongation of ε = 3.4 – 3.8 %. The comparison diagram also shows how much stress the materials can withstand, with PLA being the best performer except for the one outlier (PETG_P1). This is followed by PETG and in third place by the onyx material. Comparing all three materials with each other, it can be seen that PLA allows the least elongation in its elastic deformation range, but also quickly leads to breakage of the specimen after exceeding this range. Therefore, it can be said that PLA is certainly the material with the most brittle behavior. If you now want to realize one of your projects, you can follow these results to some extent, at least as far as tension and elongation are concerned, although the three materials naturally have other strengths and weaknesses.

The Pool Bottom Suction Robot Wheel

Anyone who has ever been to an outdoor pool knows how important it is to clean pools thoroughly. In the past, people might have been sent down there with a rag, but nowadays this is done by pelvic floor vacuums, small waterproof robots made of plastic and electronics that move back and forth tirelessly on the floor after closing time. The open-air swimming pool in Kaan-Marienborn has just such a machine, and one of its wheels was broken.

Lab manager Marios, Ms. Königsberg and Mr. Wagner from the city of Siegen, mayor Steffen Mues, operations manager Dirk Räwel and Jonas from Fab Lab, who built the wheel. Picture: City of Siegen

So we received an inquiry from the city’s sports and pools department asking if we could print something. The original manufacturer was no longer available and a new device would probably have blown the already tight corona budget. So Jonas and Marios took care of rebuilding the old wheel, first digitally and then printing it out in durable ABS. The mayor was also there and saw for himself that everything works – the application possibilities of Fab Lab Siegen are well received. So now spare wheels are no longer a problem and the robot is looking so confidently ahead, it has even taken on a part-time job at the indoor swimming pool at Löhrtor!

Press echo

10.07.2020 – wirSiegen
Outdoor pools: replacement wheel for pool cleaner comes from 3D printer

13.07.2020 – Westfälische Rundschau
Siegen: Wheel for outdoor pool vacuum cleaner from 3D printer

Face Visors Against The Virus

After the closure is before the start of production. After all, we, like many other public institutions, had to cease our operations on March 16. Now there were a dozen 3D printers standing around unused. MakerVsVirus and other ideas and projects that developed online in the following days invited us to do something against the virus.

Well, to make a long story short, we are now producing facial visors to reduce the risk of infection to medical personnel and other at-risk groups(the hip girls and guys also call them covid shields). The visors are given free of charge to medical facilities.

Our dear colleagues from the press office have also enriched the whole story with a little more detail and written it down here: Fab Lab of the University of Siegen prints face visors.

What Can I Do?

We can use donations of materials and assistance in making them!

Concrete we are searching for:

  • PETG-Filament 1,75mm
  • PETG-plates 0.5mm, transparent and clear
  • Elastic head hole rubber bands
  • Companies and individuals who have free 3D printing capacity themselves

Feel free to contact Peter Kubior:

Help, I Am a Medical Facility and I Need Visors!

Medical facilities interested in the facial visors can contact Peter Kubior by email:

I Am from The Press and Want to Know More!

Please contact our press office directly for further questions.

Stay healthy. #physicaldistancing not #socialdistancing
Your Lab-Team!

Pressreview

Cytrill – Game Controller Made in Siegen

Hackspace Siegen has developed a single-board computer for gaming, education, and experimentation that allows over 32 people to play together on one screen at the same time – a collaborative project for which our Fab Lab, among others, was used. From hardware to games, everything at Cytrill is open source.

It took about a whole year until the members of HaSi could hold the first finished controller in their hands. The idea was there, but a lot of thought went into the implementation: what should the game controller look like in the end? Which design is best for the use? In the end, a small, colorful single-board computer was created, which is similar in appearance to well-known controllers. Apart from the many buttons, the minimalistic, differently colored grips, which are plugged into the sides of the board, are striking. These grips were printed from PLA with the Luzlbot in our Fab Lab.

In the future, however, a second variant will also be created, in which two transparent Plexiglas plates are used instead of the grip panels, so that the complete circuit board remains visible. This variant is to be produced as a prototype in our lab using laser cutting.

Meanwhile, there are already several games for the controller: “Wallhack” (similar to Achtung the Curve), “RaceCtrl” (a car race), “Crystal Mett” (a game in which you have to collect crystal pigs in teams) and “SpaceCtrl” (a spaceship game). All games were created in the open source game engine Godot and so there is a GD script that controls the LEDs on the controllers that show the status or the current game color. The board itself is based on an ESP8266 radio module and has four small joysticks on each side. The controllers have a USB interface, but this is only used for loading and programming. Wifi is used to connect to games and applications, and power is supplied via a battery. The plates are decorated with an octopus and gold details.

Cytrill and individual games could already be tested in public, for example (as seen above) on the Day of Technology or the Siegen Art and Culture Week Art!Si, and gave pleasure to both young and old. The small colorful controllers attracted attention and as soon as they were tried out, some could hardly detach themselves from them. People who didn’t know each other before played against and with each other with visibly a lot of fun, much to the delight of the developers.

In the future, Cytrill will be used in workshops at our Fab Lab, but also for university teaching. The invention shows that the hacker and maker culture has already arrived in Siegerland and that it enables jointly developed, innovative projects.

Cytrill on detail:

Zeit.Raum – Making Siegen come alive

The interdisciplinary research project ZEIT.RAUM Siegen is being carried out in close cooperation with citizens and aims to make the city of Siegen experience and understand its space and history in a collaborative way using innovative technology. ZEIT.RAUM is designed to facilitate collaboration and exchange between all interested parties – from academics and students to schoolchildren and amateur historians – about the city’s history, present and future. This opens up new forms of knowledge generation and transfer.

The project consists of two interlinked components: A touchable table-sized city model for interaction, produced using various digital fabrication processes and exhibited in the Siegerland Museum. Built-in sensors enable an interactive experience of the city and its history, which also stimulates individual memories. The second central element of the project is the Stadtwiki, a collaborative digital platform on Siegen’s city history, which is being developed by and for citizens. In addition to collecting information, it also serves as a forum to discuss the meaning of the data collected. Places of remembrance are identified, processed and reflected upon. All components of the project should be designed in such a way that they are easily accessible, understandable and easy to use for all interested parties.

One of the first test prints for the interactive city model

The role of the Fab Lab

We at Fab Lab are also involved in the project on several levels, especially in the creation of the interactive city model. The existing virtual 3D model of the city of Siegen, which was created by Prof. Jarosch, serves as the data basis for this. The topography is milled out of a large plate in the Lab. Which material is best suited for this is currently being tested. The true-to-the-original buildings of the city installed on it, on the other hand, are printed with the 3D printers in the Fab Lab. The sensor technology that will later be installed in the city model, which should be as user-friendly as possible, is also being developed in our lab. Several students are also involved in the project, working on individual components of the project within the framework of qualification theses.

Paper prototype for the interaction concept of the city model

Current developments

Currently, students are working on the design of the interaction concept and have, among other things, created a paper prototype of the city model. Likewise, the first prototypes for the city model have already been successfully printed and the sensor technology extensively tested. The model is printed with conductive filament so that the sensors can later be built directly into the city model. As part of this initial technical work, a developer board (see cover picture) was also created on which the following were installed: Arduino-Leonardo, Raspberry Pi 2, CAP1188-Breakout, 3D-printed touch sensor and 3D-printed matrix.

Test of the sensor technology to be installed in the city model

During one of our last project meetings, a first model of the Nikolaikirche – probably the best known landmark of the city of Siegen – was already printed. It took our Ultimaker a whole three hours to make the 1:9000 scale model.
Here you can see the result:

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Other project partners

In addition to the Fab Lab, the University of Siegen also involves the Chair of Didactics of History headed by Prof. Dr. Bärbel Kuhn, the Chair of Practical Geodesy and Geoinformation headed by Prof. Dr. Monika Jarosch and the Chair of Computer Supported Group Work headed by Prof. Dr. Volkmar Pipek. The realisation was made possible by the support of the university and the Friends and Patrons of the Siegerlandmuseum, who see the project as an investment in the future of the Siegerlandmuseum. The Siegerland Museum is to be strengthened by ZEIT.RAUM in its role for cooperative and inclusive historical work in and with the region.

We will of course keep you informed about further developments of the project in and around the Lab.

The origin of Fab Lab Siegen

Efforts to establish a Fab Lab at the University of Siegen are not entirely new. On a smaller scale, similar activities have already been carried out at Faculty III:

The HCI lab there also provides infrastructure (e.g. 3d printers) to some extent. Even though the HCI Lab is also quite open in principle, there are no Open Lab Days here, the equipment is not extensive, the area is very small and, in addition, the room is often needed for chair activities and can then of course not be used by everyone. However, we explicitly mention the HCI-Lab here, as its operation has already created quite a bit of expertise, especially in areas such as 3d printing or also Arduino. The Fab Lab Siegen and the HCI-Lab will therefore collaborate closely (e.g. for courses and workshops) and possibly consolidate hardware and equipment in some cases.

Hackspace Siegen

It is always impressive how many exciting, self-organized and open activities are already happening in a rather small city like Siegen. One such venture is Hackspace Siegen e.V. (HaSi).

A hackspace and a Fab Lab are conceptually quite similar – both are open, creative environments where projects can be realized, lectures and workshops are held, and quite a few other exciting things happen. Basically, though, you can say that a Hackspace is more software-oriented, while in a Fab Lab you focus more on production and hardware with machines and tools. For this reason, both concepts complement each other perfectly and Fab Lab and HaSi will work in lively exchange, support each other for projects and make good use of the different competences!