This work presents a three-dimensional virtual simulation experiment for material deformation and failure that provides visualized experimental processes. Through a set of experiments, users can become familiar with the equipment and learn the operations in an immersive and interactive learning environment.
This work presents a set of comprehensive virtual experiments to detect material deformation and failure. The most commonly used pieces of equipment in mechanics and material disciplines, such as a metallographic cutting machine and a high-temperature universal creep testing machine, are integrated into a web-based system to provide different experimental services to users in an immersive and interactive learning environment. The protocol in this work is divided into five subsections, namely, the preparation of the materials, molding the specimen, specimen characterization, specimen loading, nanoindenter installation, and SEM in situ experiments, and this protocol aims to provide an opportunity for users regarding the recognition of different equipment and the corresponding operations, as well as the enhancement of laboratory awareness, etc., using a virtual simulation approach. To provide clear guidance for the experiment, the system highlights the equipment/specimen to be used in the next step and marks the pathway that leads to the equipment with a conspicuous arrow. To mimic the hands-on experiment as closely as possible, we designed and developed a three-dimensional laboratory room, equipment, operations, and experimental procedures. Moreover, the virtual system also considers interactive exercises and registration before using chemicals during the experiment. Incorrect operations are also allowed, resulting in a warning message informing the user. The system can provide interactive and visualized experiments to users at different levels.
Mechanics is one of the basic disciplines in engineering, as shown by the emphasis placed on the foundation of mathematical mechanics and theoretical knowledge and the attention given to the cultivation of students' practical abilities. With the rapid advancement of modern science and technology, nanoscience and technology have had a huge impact on human life and the economy. Rita Colwell, the former director of the US National Science Foundation (NSF), declared in 2002 that nanoscale technology would have an impact equal to the Industrial Revolution1 and noted that nanotechnology is truly a portal to a new world2. The mechanical properties of materials at the nanoscale are one of the most fundamental and necessary factors for the development of high-tech applications, such as nano-devices3,4,5. The mechanical behavior of materials at the nanoscale and the structural evolution under stress have become important issues in current nanomechanical research.
In recent years, the development and improvement of nanoindentation technology, electron microscopy technology, scanning probe microscopy, etc., have made "in situ mechanics" experiments an advanced testing technique important in nanomechanics research6,7. Obviously, from the perspective of teaching and scientific research, it is necessary to introduce frontier experimental techniques into the traditional teaching content regarding mechanical experiments.
However, experiments of microscopic mechanics are significantly different from macroscopic basic mechanics experiments. On the one hand, although the relevant instruments and equipment have been popularized in almost all colleges and universities, their number is limited because of the high price and maintenance cost. In the short term, it is impossible to purchase enough equipment for offline teaching. Even if there are financial resources, the management and maintenance costs of offline experiments are too high, since this type of equipment has high-precision characteristics.
On the other hand, in situ mechanics experiments such as scanning electron microscopy (SEM) are very comprehensive, with high operational requirements and an extremely long experimental period8,9. Offline experiments require students to be highly focused for a long time, and misoperation can damage the instrument. Even with very skilled individuals, a successful experiment requires a few days to complete, from preparing qualified specimens to loading the specimens for in situ mechanics experiments. Therefore, the efficiency of offline experimental teaching is extremely low.
To address the above issues, virtual simulation can be utilized. The development of virtual simulation experiment teaching can address the cost and quantity bottleneck of in situ mechanics experimental equipment and, thus, allow students to easily use various advanced pieces of equipment without damaging high-tech instruments. Simulation experiment teaching also enables students to access the virtual simulation experiment platform via the internet anytime and anywhere. Even for some low-cost instruments, students can use virtual instruments in advance for training and practice, which may improve teaching efficiency.
Considering the accessibility and availability of web-based systems10, in this work, we present a web-based virtual simulation experimentation system that can provide a set of experiments related to fundamental operations in mechanics and materials, with a focus on the in situ mechanics experiment.
In this work, the procedures of the microcantilever beam fracture experiment with cracks are discussed as follows, which is open for free access via http://civ.whu.rofall.net/virexp/clqd. All the steps are conducted in the online system based on the virtual simulation approach. Institutional Review Board approval was not required for this study. Consent was obtained from the student volunteers who took part in this study.
1. Accessing the system and entering the interface
2. Preparation of the materials
3. Molding the specimen
4. Specimen characterization
5. Specimen loading and nanoindenter installation
6. SEM in situ experiment
The system provides clear guidance for the user's operations. First, beginner-level training is integrated when a user enters the system. Second, the equipment and the laboratory room to be used for the next-step operation are highlighted.
The system can be used for several different educational purposes for different levels of students. For example, Figure 1 includes seven of the most commonly used types of equipment in the mechanical and material disciplines, namely, the metallographic cutting machine, high-temperature universal creep testing machine, metallographic specimen inlaying machine, polishing machine, optical microscope, SEM, and micro- and nano-mechanics testing system. In the guidance for beginners, the user can learn about the descriptions of all the equipment used in the experiment. Then, all the equipment is used one by one to complete the experiment. The students can choose the equipment for repetitive experiments until they master the operating skills.
Figure 3 and Figure 4 also demonstrate that the system can enhance the design of the experimental scheme combined with the experimental operations, which can provide instant validation. In Figure 3, the user should choose to place the specimen in the correct direction to create a molded specimen. Figure 4 shows the interface for using the metallographic specimen inlaying machine, which also shows the results (as indicated at the bottom-left corner of Figure 4) of the previous step after the user confirms the selection, as shown in Figure 3. Figure 7 illustrates the in situ mechanics experimental results of the micro-cantilever beam with preset cracks. Through the analysis of the results, the user can determine how the results were obtained.
This protocol simulates the scenario in which the students are required to evaluate the load size and loading time of the rheological experiment of the parallel plate according to the length-to-diameter ratio of the specimen to be prepared. The experimenter needs to analyze the relation of the length-to-diameter ratio of the viscous fluid flowing into a cylindrical hole mold, the pressure p0, and the time t with a diameter of d under the action of constant pressure p0. This relation is shown below:
where L is the length, d is the diameter of the cylindrical hole mold, p0 is the constant pressure, η is the material viscosity, and t is the loading time. Once p0, η, and L/d are given, t can be calculated. If L/d doubles, the loading time will be four times larger than before. Figure 8 illustrates the relationship between the length-to-diameter ratio of metal glass flowing into the mold hole and time.
In real-world experiments, it was found that students often used a trial-and-error approach-that is, constantly adjusting the load size or loading duration until the required sample was finally made. In this protocol, an interactive interface is provided to validate the theoretical knowledge, and the loading time is determined according to the provided parameter values (material viscosity, initial sample size, and load size). A guiding question is provided as follows: "Metal glass is a Newtonian fluid with a viscosity of η = 107 Pa·s at the die casting experimental temperature. The fluid has no slip at the mold contact boundary. It is necessary to prepare a cylindrical specimen with a length-to-diameter ratio of 5. If the experiment can apply a large amount of pressure of 100 MPa, how long should the loading time be? If the length-to-diameter ratio is increased by 1x, how many times does the loading time increase by?" The students should figure out the answers, set the test scheme accordingly, and then conduct their experiments.
After the experiment, the students are asked to answer a few questions of different types, such as fill-in-the-blank questions and single-answer/multi-answer multiple-choice questions (MCQ), which focus on the key steps during the virtual simulation experiment to enhance their theoretical knowledge and experimentation. Table 1 shows the question examples for the online exam exercise after the experimentation. With integrated exercises, users can systematically review the entire process of the experiment and connect the theory with the experimentation.
The set of experiments offered by the implementation of the proposed virtual simulation mean that the following visualized and interactive knowledge-enhanced and skill-enhanced experiences can be provided: 1) an immersive virtual learning environment where users can "walk" through and understand the layout of the laboratory rooms and the details of each piece of equipment; 2) operations on different typical pieces of equipment in the mechanical and material disciplines to master operating skills; 3) safety awareness enhancement through wrong operations and warnings; 4) repetitive experiments and shorter time experiments instead of the duration of experiments; 5) following the protocol of conventional laboratories as closely as possible so that users can be familiar with the procedures and the "dos" and "do nots" even in the virtual environment.
Conventionally, due to the limited amount of equipment and the occupation of graduate students for research purposes, undergraduate students rarely have the chance to conduct experiments with physical equipment. The virtual simulation system that integrates different types of equipment can help provide concurrently accessible and repeatable experiments to enhance their laboratory skills. After its deployment, the virtual system was applied in the autumn semesters of the 2020 and 2021 academic years for students with engineering mechanics backgrounds. Table 2 shows the results of the experiment, which include the mean completion time, the standard deviation of the completion time, and the average scores of the different years. The average score (100 in total) is calculated based on the evaluation of the experiment (70%, evaluated by the system) and the laboratory report on the web (30%, evaluated by the teacher). The results demonstrate that students can, on average, complete the experiment in ~73 min using a web browser, which is time efficient and verifies the efficiency of the web-based system based on the virtual simulation approach. In 2022, we performed a study to demonstrate the efficiency of the proposed protocol. Students from two classes with engineering mechanics backgrounds (two classes with the same teacher and the same class modules, divided into two classes for class size reasons) were divided into two groups (one class for each group). The students from Group 1 attended the physical laboratory to learn the theoretical knowledge and watch the operations from the teacher, while the students from Group 2 used the virtual interface that was developed based on the physical laboratory (including the layout and the equipment) for their experiment. Table 3 shows the online exam results (with a total score of 10) for the students without (Group 1) and with (Group 2) the virtual interface experience. It can be concluded that the students with the virtual interface experience performed better than those without the experience.
Figure 1: The developed three-dimensional equipment used during the experiments. It can be concluded that through this virtual simulation experiment, the user can be trained to be familiar with the most commonly used equipment in the mechanical and material disciplines. Please click here to view a larger version of this figure.
Figure 2: Highlighted high-temperature universal creep testing machine in the virtual simulation laboratory room. After completing the previous step (cutting the specimen), the next step is generated automatically, which either highlights the machine (when the machine is nearby) or the pathway leading to the machine (when the machine is not nearby). Please click here to view a larger version of this figure.
Figure 3: The interface for choosing the placement direction of the specimen. The user should choose the correct placement direction of the specimen to continue with the next step. Please click here to view a larger version of this figure.
Figure 4: The interface for using the metallographic specimen inlaying machine. The results of the previous step after the user confirms the selection (in Figure 3) are shown in the bottom-left corner. Please click here to view a larger version of this figure.
Figure 5: The interface with a highlighted pathway guidance. The user is guided to enter a room for the polishing and corrosion of the specimen. Please click here to view a larger version of this figure.
Figure 6: Wiring for the SEM machine. The user should connect the wires to continue with the experiment. Please click here to view a larger version of this figure.
Figure 7: In situ mechanics experimental process results of the micro-cantilever beam with preset cracks. The two curves show an example of the in situ mechanics experimental results of amicro-cantilever beam with preset cracks. (A) Displacement-time curve, (B) stress-strain curve. Please click here to view a larger version of this figure.
Figure 8: Calculation based on theoretical knowledge. The relationship between the length-to-diameter ratio of metal glass flowing into the mold hole and time. Please click here to view a larger version of this figure.
Figure 9: The warning shows that a wrong operation has damaged the scope. Users can click the button to level up/down the SEM detector. However, if they level up too much, the SEM detector will be damaged. Please click here to view a larger version of this figure.
Figure 10: The e-notebook for the online registration before using a chemical. Before the corrosion process, the user must register it in the notebook, which is the same as the procedure in the physical laboratory. Please click here to view a larger version of this figure.
ID | Exam question type | Question details | Provide choices |
1 | Fill-in-the-blank question | In this experiment, __ solution was used to corrode the silicon wafer. | None |
2 | Single-answer MCQ | When the high temperature universal creep testing machine is used for the experiment, which of the following materials can be regarded as Newtonian fluid? | A. Conventional metal |
B. Amorphous alloy | |||
3 | Single-answer MCQ | If a specimen is estimated to withstand the maximum force of 60mN, then in the range selection, choose InForce 50 or InForce 1000? | A. InForce 50 |
B. InForce 1000 | |||
4 | Multi-answer MCQ | Nanoindenter can be used to measure? | A. Hardness |
B. Modulus of elasticity | |||
C. Fracture toughness | |||
D. Viscoelasticity | |||
5 | Single-answer MCQ | SEM is an abbreviation for | A. Optical microscope |
B. Scanning electron microscopy | |||
C. Transmission electron microscopy |
Table 1: Question examples for the online exam exercise after the experimentation. Users are required to complete different types of questions so that they can systematically review the entire process of the experiment and connect the theory with the experimentation.
Year | Number of students | Mean completion time | Standard deviation of the completion time | Average score |
2021 | 58 | 71 min and 46 s | 11 min and 39.5 s | 79.83 |
2020 | 77 | 73 min and 3 s | 11 min and 15.4 s | 80.21 |
Table 2: The results of experiments in different years. Students with engineering mechanics backgrounds completed the experiments in two different academic years.
Group ID | Number of students | Average score | Standard deviation of the score |
1 | 18 | 5.56 | 1.15 |
2 | 22 | 8.09 | 1.27 |
Table 3: The online exam results (with a total score of 10) for students without (Group 1) and with (Group 2) the virtual interface experience. Students with engineering mechanics backgrounds were divided into two groups in 2022 to demonstrate the efficiency of the protocol.
One of the advantages of virtual simulation experiments is that they allow users to conduct the experiments without concerns regarding damaging the physical system or causing any harm to themselves11. Thus, users can conduct any operations, including either correct or wrong operations. However, the system gives the user a warning message that is integrated into the interactive experiment to guide them to conduct the experiments correctly when a wrong operation is conducted. In this way, users can learn the correct operations. For example, when a user conducts operations on the SEM, as shown in Figure 9, they may level up the SEM detector too much and damage it by accident.
Similar to hands-on experiments in physical laboratories, users who conduct virtual experiments should also follow correct procedures, which can potentially enhance their experimentation and safety awareness. For example, as illustrated in Figure 10, when preparing a KOH solution for the corrosion process of the specimen into a metallographic specimen, the user should register in a notebook before using the chemical.
Although this system provides a complex and comprehensive virtual environment for material deformation and failure experimentation, the main limitation is that it currently lacks user customizations. Users follow the steps to conduct experiments, and they rarely have a chance to implement their ideas. However, the system can be improved to provide students with more freedom to implement their ideas and create their own designs and implementations.
Three-dimensional virtual simulation has been an important topic throughout the world during the past decade in terms of providing immersive interfaces for engagement and learning12,13. Studies regarding virtual simulation have been conducted in various disciplines, such as in control engineering14 for safety considerations15 and in chemical engineering for production practice16. In the materials and mechanics discipline, the system can be used for the training of students regarding experimental protocols, the use of equipment, and the verification of theoretical knowledge. With respect to existing methods, the proposed virtual simulation approach can be accessed by users at any time from anywhere as long as internet and a web browser are available, meaning this approach is cost-effective and highly efficient. By providing seven different types of costly equipment, the online system allows users to repeatedly enhance their operations and laboratory skills in this single online system.
The system can be used in combination with traditional teaching and learning in future applications of the technique. For example, the system could be combined with hands-on experiments. Students could conduct virtual simulation experiments before they conduct hands-on experiments in conventional laboratories. Compared with conventional methods, the system is interactive and immersive. Further to the benefits provided by traditional education, virtual simulation-based experimental teaching provides a full range of auxiliary functions, which can exercise students' ability to use the knowledge they have learned to solve practical problems. Additionally, this type of teaching also cultivates students' research interests and sense of innovation by training them to master the testing techniques, methods, and principles of advanced micro- and nano-scale mechanical experiments and effectively helps students improve their professional and comprehensive qualities.
The authors have nothing to disclose.
This work was supported in part by the Fundamental Research Funds for the Central Universities under Grant 2042022kf1059; the Nature Science Foundation of Hubei Province under Grant 2022CFB757; the China Postdoctoral Science Foundation under Grant 2022TQ0244; the Wuhan University Experiment Technology Project Funding under Grant WHU-2021-SYJS-11; the Provincial Teaching and Research Projects in Hubei Province's Colleges and Universities in 2021 under Grant 2021038; and the Provincial Laboratory Research Project in Hubei Province's Colleges and Universities under Grant HBSY2021-01.