140

Virtual Experiment System for Metal Creep Performance Testing Based on VRML

TANG Jia-li, LIU Yi-jun, WU Fang-sheng

College of Computer Science and Engineering

Jiangsu Teachers University of Technology

Changzhou 213001, China

e-mail: tangjl@jstu.edu.cn

Abstract—A virtual experiment system for metal creep

performance testing is built by virtual reality modeling

language (VRML). The structure, function and design

principles of the system are described and its implementation

procedure is also discussed. The key development process,

including object modeling, 3D scene building, VRML

connecting to the real-time database, design of interactive

virtual 3D scene and complex virtual interaction, is illustrated

in this paper. In addition, the following key problems have

been solved during the system realization: virtual models

building and geometrical transforming, database designing

and optimizing, 3D virtual experimental scenes combining

dynamically, the realization of database accessing and the

communication of virtual entities.

Keywords- creep performance test; metal; virtual experiment;

VRML

I. INTRODUCTION

Virtual reality (VR) is a kind of human-computer interaction system, which may found and experience the virtual world [1, 2]. It can build the virtual environment using computer simulation technology, therefore, carry on the direct control through the data glove or the head mounted display and other interactive equipments. In detail, a virtual environment in a specific scope with vivid integrated visual, auditive and haptic sense is created by using the contemporary high technology which takes the computer as the core [3]. Along with the virtual reality and computer simulation technology development, because of its potential advantages of quick result, the virtual experiment becomes the hot spot of current research. The people may freely enter the virtual experiment laboratory (VEL) at any time to operate each kind of instrument and carry on different experiment with the immersion feeling of experience personally.

This paper discusses to use virtual reality modeling language (VRML) [4] to set up the virtual three dimensional experiment instrument models and make use of visual programming language VB 2005 to develop a platform with complex interactive actions. This platform of the Virtual Experiment System for Metal Creep Performance Testing (MCPT-VES), has provided a friendly interface, enables the user to be possible to compose the virtual three-dimensional experiment scene intuitively, to use the keyboard or mouse to control three dimensional testing machine in the virtual scene for movement and realize the virtual scene transfer from the static state VRML scene to the interactive VRML scene, thus

to control the virtual model movement to complete experiment's each movement. The system mainly deals with the creep deformation experiment and it provides the strong secondary development function with dynamic revision, increase and deletion of the experiment project.

II. SYSTEM DESIGN

A. Overall function and structure

The lab system's virtual simulation experiment part is based on the C/S pattern, realized together by VB and VRML. This part is in charge of the invocation from static scene to virtual scene, and the interaction between node domain and the event. So it controls the motions of 3D models according to the user’s instructions. The system mainly includes the experiment plan module, virtual instrument repository module, material performance library module, performance parameter module, virtual scene module and data processing module and so on. These modules are connected by dynamic data exchange (DDE) [5].

Figure 1 Virtual experiment procedure of the client

In the C/S pattern, the virtual experiment calls the local client procedure. The user visits the application server through the client procedure. The application server obtains the 3D virtual instrument model, experiment sample and its corresponding parameters from the model base and the performance library, and transmits them to the client. The user may select the virtual instrument and the sample through this mode, composite the virtual experiment scene, set up virtual experiment parameters and carry on the experiment. After finishing the experiment, the user can

978-1-4244-5848-6/10/$26.00 ©2010 IEEE

141

process the experimental data and save related information to the user database. Virtual experiment flow of the client is demonstrated as Figure 1.

B. Design principle

VRML is a kind of three-dimensional modeling and rendering graphic descriptive language, it regards “virtual world” as “scene”, everything in the “scene” as “object” (i.e. “node”). VRML constitutes the wrl file through describing each object. Communication may be achieved by using VB API functions with VRML. Thus the control and interaction of the prototype node domain can be obtained by this method.

First, we build three-dimensional models and spatial scene needed by the virtual laboratory, including stretcher, drop-testing machine, creep tester, vernier caliper and other test instruments and measuring tools. Due to Pro/E’s [6] precise and highly effective modeling method together with 3DS MAX’s [7] material high-quality lighting processing, the system may clearly reappear the experiment instruments of the real world. For example, two parts of the creep testermodel are shown in Figure 2.

Figure 2 HALF furnace and supporting frame models of the creep tester

Then the wrl file can be outputted through File menu Export order. In VRML, the scene chart consists of each kind of node. The node communicates through the event and the event disseminates through the route in the scene chart. The key point of realizing the interactive virtual experiment lies in controlling the VR entity to interact with the user alternately, which needs the TimeSensor, TouchSensor, PositionInterpolator and other script nodes to transmit time through the route. This all needs to add control button in virtual reality scene and to realize interaction between the virtual scene and the user [8].

Finally, we integrate VRML scene in VB 2005’s control platform and make communication between VB and VRML through API functions. For example, we define PROTO prototype node in the VRML document [9]. Then the user-defined domain and event play the connection role in it. As a result, by using API functions, we control the used prototype node domain and produce interaction between the console and the virtual scene.

III. REALIZATION OF MODELING AND VIRTUAL

INTERACTION IN MCPT-VES

A. VRML model building

Geometric and physical models are necessary when indicating a 3D model perfectly. Geometric model expresses the VR entity characteristics like shape, appearance, location and texture, only showing its static characteristics. However, physical model expresses its dynamic attributes, like speed, acceleration, displacement, deformation, etc.

There are two solutions to build geometric models. One is to write source codes and save as wrl format file. The other way is to make 3D models with Third-Party Modeling Software (like 3DS MAX or Maya), import them into VRML system with wrl format, edit their location and relationship with VR world and finally form the whole.

The building of physical models should be achieved by scripts, TimeSensor, space location nodes and SpaceSensor. TimeSensor sends clock information and scripts calculate new physical characteristics of the entity according to its movement attributes [9].

B. Real-time Access to the Database of VRML

VRML realizes information exchange to database with embedded JavaScript. The script language is encapsulated in the url domain of script nodes. The language changes the gotten data from database to the format supported by its own. The process is achieved by VRML and JavaScript mixed programming [10]. In detail, we declare and insert JavaScript into the url domain of script node, connect and operate the database in the script, then get the VRML-supported format and encapsulated data, and finally transmit from it to the interface domain of another node. Part of the source code is shown as below:

DEF example script {url “JavaScript: #Declare the type of script languagethis.database.connect(databasetype,servername,username

,password,databasename)#Connect to the databaseRecordSet=this.database.execute(select * from

databasetable where…) #Search data and recordVariable_changed= RecordSet”} # Encapsulate data and send to output interface

C. Development of Interactive Virtual Scenes

It is important to control VR entities to interact with users when they are performing a virtual experiment. For example, users can have control over the movements of creep tester,including collets opening, sample loading, clamping, stretching, compressing and stopping. What we should do is to add control buttons in virtual scenes and establish data communication between human and computer [11].

When users click the Command button, TouchSensor is triggered. Though the Route and function defined by Script, TouchTime of TouchSensor is evaluated to StartTime of TimeSensor, then TimeSensor begins to time. Because TimeSensor has been defined a cycle time, it generates

142

Fraction_changed when time changes. In addition, the fraction value is set to Set_fraction of Position Interpolator though corresponding routes. According to the value, Position Interpolator calculates the defined movement route and gets Position_changed of the time. The value is sent to Set_translation of the VR entity through the routes again. Finally the entity changes the location and it begins to make motions. Therefore interactive motion will be accomplished after defining the corresponding routes of different VR entities in the virtual scene and making similar above-mentioned procedures [12].

When users select virtual equipments, samples or measuring tools, the control program finds the VRML files (wrl format) from virtual apparatus module and their attributes, makes grouping and geometric transformation to assemble the required virtual experimental scenes by Transform, Inline other grouping nodes.

For instance, when a user begins a metal creepexperiment, firstly he/she must select the vernier caliper to measure the metal sample. As a result, MCPT-VES reads their VRML files, attributes from virtual scene module, makes grouping and geometric transformation orderly, and assembles the virtual experimental scenes. Then the experimenter can measure the diameter of metal sample on screen. If different sample is selected, MCPT-VES loads different virtual experimental scenes for measuring.

The screenshot of adding third load when performing creep testing is shown in Figure 3.

Figure 3 Effect of adding third load to the metal sample

When the set time is up, MCPT-VES gets the factors of temperature T, deformation l, time t and stress σ from the database. Then the drawing model draws the creep curve automatically (as shown in Figure 4).

IV. CONCLUSIONS

As a typical interactive virtual experiment platform, MCPT-VES was developed by VRML to perform testing of metal creep performance. Users can select virtual apparatus and samples, make open material experiments in the organized virtual scenes and refer to online knowledge database when they have any questions. The experimental process is more interacted and visible by using VR technology than traditional material experiment education.

Figure 4 Interface of drawing creep curves

ACKNOWLEDGMENT

This work is supported by the High Education Natural Scientific Foundation of Jiangsu Province, P.R. China under the research grant No. 08KJB430003, and by the Science and Technology Project Foundation of Changzhou City, P.R. China under the research grant No. CE2008089.

REFERENCES

[1] H. X. Liu, “Interactive Virtual Logistics System Based on VRML and Java3D”, Computer Engineering, vol. 21, Nov. 2008, pp. 259-264.

[2] S. Maureen, “Virtual Reality Modeling Language”, IEEETransactions Computer Graphics and Applications, vol. 19, Feb. 1999,pp. 17-18.

[3] Z. X. Sun, R. C. Wang, S. D. WANG, “Research and Implementation of Distributed Virtual Simulation Platform Based on Components”,The Journal of China Universities of Posts and Telecommunications,vol. 11, Feb. 2004, pp. 7-13.

[4] A. H. Fan, Z. D. Hu, “Modeling technology of virtual reality”,Computer Simulation, vol. 14, Apr. 1997, pp. 64-66.

[5] H. Steven, “Technical Skills of Visual Basic 6”, China Machine Publisher, Jan. 1999.

[6] Q. Yu, P. Lu, “Basic Courses of Pro/E Mold Design”, Tsinghua University Publisher, Oct. 2005.

[7] H. Zhang, A.N. Wang, “Basic Courses of 3ds Max 8”, Tsinghua University Publisher, Mar. 2006.

[8] C. B. Chen, W. Zhu, L. S. Liu, “Research on a virtual experiment platform for programmable devices”, Computer Engineering and Science, vol. 26, Jul. 2004, pp. 77-78.

143

[9] J. K. Yan, G. Y. Gan, J. L. Sun, “Electronic Ceramics Virtual Laboratory Based on VRML”, Journal of Kunming University of Science and Technology (Science and Technology), vol. 28, Jan.2003, pp. 12-18.

[10] S. Ozifrankly, “Using Semantic Rules Database to Dynamically Set up the ICSpace Virtual Building”, Springer-Verlag GmbH, vol. 17,Jun. 2002, pp. 2503-2505.

[11] R. N. David, “Building virtual worlds with VRML”, IEEE Transactions on Computer Graphics and Applications, vol. 19, Feb. 1999, pp. 18-29.

[12] J. H. Sun, “Development of Virtual Interactive Assembly Platform based on VRML”, Computer Applications, vol. 22, Oct. 2002, pp. 101-102.