Engineering Solid Mechanics

Transcription

1 }} Engineering Solid Mechanics 1 (013) Contents lists available at GrowingScience Engineering Solid Mechanics hoepage: Designing and anufacturing of a drop weight ipact test achine F. Taheri-Behrooz, M.M. Shokrieh * and H.R. Abdolvand Coposites Research Laboratory, School of Mechanical Engineering, Iran University of Science and Technology, Tehran, , Iran A R T I C L E I N F O A B S T R A C T Article history: Received January 0, 013 Received in Revised for July,, 013 Accepted 6 August 013 Available online 7 August 013 Keywords: Drop Weight Test Manufacturing Toughness Coposites Ipact A state of the art instruented Drop Weight Ipact Tester Machine was developed in Iran University of Science and Technology which easures the energy absorption of coposite aterials under ipact load. The output of the achine is used to draw load- tie graph and calculate the aount of energy absorbed by the speciens. The achine was equipped with various sensor systes to easure the velocity of the ipactor just before it contacts the specien and the aount of contact force, and with a data acquisition syste to record the force and tie history. Capability of testing according to any different types of standards and capability of studying behaviour of the specien after ipact are two iportant characteristics of this achine. This designed syste, after anufacturing and calibration, was installed and successfully utilized. 013 Growing Science Ltd. All rights reserved. 1. Introduction Because of high specific strength and odulus, low specific density and corrosion resistance, fibre reinforced plastics are used in vast ajority of fields such as aerospace, transportation and building structures. In order to optiize designing with these aterials it is necessary to perfor standard tests and find out their echanical properties. Toughness is an iportant property of coposite aterials and shows energy absorption capacity of the specien. This energy is easured by ipact testing. Izode and Charpy are two popular ethods of ipact testing but with any restrictions such as: necessity of using notch in the specien and liitation on the agnitude of applied load. There is another ethod which use falling weight to easure energy absorption capacity of aterials, called Drop Weight Ipact Testing (DWIT) with any advantages as entioned below: Capability of testing based on different types of standards and shapes. * Corresponding author. E-ail addresses: shokrieh@iust.ac.ir (M. M. Shokrieh) 013 Growing Science Ltd. All rights reserved. doi: /j.es

2 Results of tests are in for of load-tie and absorbed energy- tie forat, so the history of failure can be studied ore precisely. Recording 100 data in s akes the result ore accurate and precise. Capability of testing of speciens under any slope. Capability of investigating of behaviour of speciens after ipact test. Ghasei-Nejhad and Parvizi-Majidi (1990) and Madjidi et al. (1996) utilized a DWIT achine which had ability to test specien with any angle in ounting, also they studied copressive behaviour of the specien after ipact test. Under ipact loads, coposite aterials show different responses in coparison with etals. Metals under ipact loads show a short elastic response that followed by a long plastic deforation. While, in coposites, elastic response is followed by different odes of failure such as delaination, atrix cracking and fibre breakage. In fact in etals, the ipact energy is absorbed by plastic deforation. However, coposites absorb energy by different failure odes. Coposites response under ipact force was studied by any researchers based on the developed drop weight ipact test achines. For instance DWIT achines have been developed by (Zoller (1983); Winkel and Adas (1985); So and Francis (1991); Abur et al. (1995); Toropov and Grosso (1998); Barr and Baghli (1998) and Gunawan et al. (011)). The research results show that the duration of Ipact is about illisecond. This is an iportant factor for choosing the appropriate load cell and data acquisition instruent. The ain goal of this research is to design and anufacture of a DWIT achine which serves the aboveentioned entioned advantages over the traditional Izode and Charpy test ethods.. Energy Absorption Calculations The ost iportant easurable factor by a DWIT achine is the energy absorption, although, the load-tie graph has useful inforation. The traditional way of easuring energy absorption was calculating kinetic energy before and after ipact. However, a DWIT easures the load versus tie ore accurately and precisely and illustrates energy absorption history. Different failure odes caused by ipact can be studied fro the load-tie history graph obtained fro the achine. Change in kinetic energy is calculated by equations 1 and 1 1 v1 v F dy, (1) F dy Absorbed Energy, () where is the ass of ipactor, F is the force, y is the displaceent, 1 and are the velocity of ipactor before and after ipact, respectively. Eq. 1 is used for calibration and shows whole absorbed energy. While Eq. shows absorbed energy at every oent. An installed load cell on DWIT is used to easure F(t). Displaceent as a function of tie y(t) is obtained by double integration of the acceleration. Eqs. 3, 4, and 5 show energy absorption calculations. F( t) a( t), (3) y t) ( a( t) dt) dt, (4) ( 1 y( t) F( y) F dy. (5) F( t)

3 F.Taheri-Behrooz et al. / Engineering Solid Mechanics 1 (013) 71 A nuerical ethod is used to calculate Eq. 4, and 1 is easured experientally by a photocell. The absorbed energy at any oent is obtained by Eq. 5 if the displaceent and force as functions of tie are known. 3. Detail design of low velocity ipact test achine A general view of the design procedure of the achine is presented in this article. More inforation is available in the final report of DWIT provide by Shokrieh et al. (00). DWIT consists of any coponents such as: chases, Ipacting echanis, elevation syste, fixture systes, power and protection syste, pneuatic syste (Brake and release syste) and a data acquisition syste. Figure 1 shows the DWIT achine designed and anufactured in this research Plate of the achine Fig. 1. DWIT achine The calculations of the base plate of the achine are carried out by siulating it with a ass-spring syste. After calculating spring constant of plate, its deflection is calculated and finally the stress is obtained. Eqs. 6 and 7 are the energy equations and siulate plate with spring ass syste to find spring constant. By assuing =0 kg, g=10 /s, h=1. : 1 (6) e Ky gh 480 K (7) y The plate rigidity is as follow: 3 Et D (1 ) N (8) where e, E, k, y, h, D, t,, are energy, elasticity odulus, spring constant, deflection, release height, plate rigidity, thickness and Poisson s ratio, respectively. Fro Hooke's law and considering the distributed force (q) per unit area we have: F ky qab ky (9) where a=100 and b=00.

4 7 For a fixed rectangular plate, bending oent, deflection and stresses are as Eq. 10. For ore inforation about driving of these equations interested readers are referred to Young (1954) and Tioshenko and Woinowsky-Kreiger (1959). 4 qb y, Mx qb, M y 1qb (10) D where, and 1 are constants and M is the oent. For concentrated force acting on fixed plate we have: 6 y 6 x x M, M, M F y x 1, M F y, bt at (11) Fb a 1 1 tanh y ax tanh, 3 3 (1) D b 1,3,... cosh 4 1,3,.. sinh cosh b where F is concentrated force and. a After siplification of Eq. 1, axiu deflection, y ax, is siplified as follows: y Fb ax (13) D Table 1 shows the results of equation 10, 11, 13 and Ansys software Table 1. Results of equation 10, 11, 13 and Ansys software Method Loading Conditions y ax () (MPa) M x (N) M y (N) Tioshenko and Distributed Woinowsky-Kreiger (1959) Tioshenko and Concentrated Woinowsky-Kreiger (1959) Nuerical analysis Concentrated perfored by ANSYS Jack choosing Two pneuatic jacks have been selected for the release and shock daping systes. One jack is used for releasing ipactor at any perissible height with outer diaeter of 10 while the other pneuatic jack is used for protecting specien fro Second ipact when the first ipact was applied with the outer diaeter of 40. Operating pressure of jacks is 10 bar. Figures -a and -b show the selected pneuatic jack. (a) (b) Fig.. The selected pneuatic jack: a) release syste b) daping syste

5 F.Taheri-Behrooz et al. / Engineering Solid Mechanics 1 (013) Force easureent During the ipact the force transducer sends data to the signal conditioner. After filtering the data, an A/D card (PCL818H) converts the data to digital ode and sends the by Direct Meory Access ethod (DMA) to a coputer. DMA is the fastest way for transitting the data to a coputer without any conflict in a siultaneously reading and writing process. More inforation about force signals processing could be found in Huibert and Raphael (1991). 5. Velocity and energy easureent The absorbed energy and ipactor contact speed are easured in this research by two different ethods. In the first ethod a photocell is used for easuring initial velocity ( 1 ). When the botto edge of Ipactor plate passes through the photocell a signal is sent to the coputer. As soon as receiving this signal, a counter begins to count elapsed tie. While ipactor passing through photocell, counter continues to count tie until upper edge of ipactor passes through the photocell. Initial velocity is coputed by dividing the thickness of ipactor ( =7 ) to the elapsed tie. Also the load is easured by a load cell and finally the energy is obtained. In the second ethod by using two equations gh and e gh the velocity and the energy are calculated. The results for =0 kg and h=1. are showed in Table () for the entioned ethods. Table. Absorbed energy and ipact velocity of DWIT achine Paraeter First ethod Second ethod Error % (/s) e (J) The differences between results of two ethods are due to friction between the coponents of the achine. The flow chart of the autoation syste is shown in Fig. 3. Fig. 3. The flow chart of autoation syste

6 74 6. Brake syste As shown in Fig. 4 there are two possibilities after ipact: Failure of specien occurs: shock absorber at this case shows no reaction and the ipactor coes down and stops. If the ipactor bounce backs and after sensing the return of the ipactor by the second photocell, the progra sends a signal to the shock absorbers. After receiving the signal, shock absorbers prevent the ipactor to coe down. It is noticeable that second photocell can copute return speed, in sae way discussed on easuring 1, for the calibration of the achine. 7. Prograing All data such as load, falling and bouncing back velocities are logged with DMA ethod in PASCAL language and then are sent to MATLAB software for ore processing. Users can work with created GUI and study the test results. A saple output of DWIT in MATLAB language is shown in Fig. 4-a and Fig. 4-b. Fig. 4-a. Load-tie graph

7 F.Taheri-Behrooz et al. / Engineering Solid Mechanics 1 (013) 75 Fig. 4-b. Output of DWIT 8. Conclusions A dropped weight ipact tester achine was developed successfully which can apply ipact load to a specien with axiu speed of 4 /s and variable ass up to axiu 0 kg. Piezoelectric force transducer used in DWIT achine provides a practical alternative ethod to traditional strain gauge instruentation. During the test, the ipact speed and the tie history of contact force can be easured and recorded for further analysis. The displaceent of the ipactor during ipact would be easured by equipping the achine with displaceent sensors in the future. This designed syste, after anufacturing and calibration, was installed and successfully utilized. Acknowledgeent The authors wish to express their appreciation to the Iran University of Science and Technology for their financial supports. References Abur, D.R., Prasad, C.B. & Waters, W.A. (1995). A dropped-weight apparatus for low-speed ipact testing of coposite structures. Experiental Mechanics, 35(1), Barr, B. & Baghli, A. (1998). A repeated drop-weight ipact testing appartus for concrete. Magazine of Concrete Research, 40(144), Ghasei-Nejhad, M.N., & Parvizi-Majidi, A. (1990). Ipact behaviour and daage tolerance of woven carbon fibre-reinforced theroplastic coposites. Coposites, 1, Gunawan, L., Dirgantara, T. & Putra, I.S. (011). Developent of a dropped weight ipact testing achine. International Journal of Engineering & Technology, 11(6), Huibert, K. & Raphael, S. (1991). Modern singls and systes. Prentice Hall.

8 76 Madjidi, S., Arnold, W. S., & Marshall, I. H. (1996). Daage tolerance of CSM lainates subject to low velocity oblique ipacts. Coposite structures, 34(1), So, W., & Francis, E. C. (1991). Dynaic finite eleent analysis of solid propellant ipact test. Journal of Spacecraft and Rockets, 8(6), Shokrieh, MM. Taheri-Behrooz, F., Davaee, A.H., Akhavan, N. & Abtahi, R. (00). Drop weight ipact tester. Final Report, Iran University of Science and Technology. Toropov, AI. & Grosso, M. (1998). Dynaic calibration of ipact test instruents. Journal of Testing and Evaluation, 6(4), Tioshenko, S.P. & Woinowsky-Kreiger, S. (1959). Theory of plates and shells. McGraw-Hill. Winkel, J.D. & Adas, D.F. (1985). Instruented drop weight ipact testing of cross-ply and fabric coposites. Coposites, 16(4), Young W. C. (1954). Roarks forulas for stress and strain. McGraw-Hill. Zoller P. (1983). Instruentation for Ipact testing of plastics. Polyer Testing, 3,