Instrumented Pendulum Impact Testing for Plastics

Transcription

1 Prüfen mit Verstand Instrumented Pendulum Impact Testing for Plastics testxpo 2015 Instrumented Impact Testing

2 Agenda Pendulum Impact Testing - Basics Instrumented Impact Testing Tests and Curves Summary Instrumented Impact Testing 2

3 Pendulum Impact Testing - Basics Zwick s HIT series - a complete product range for impact testing Charpy Izod 5 Joule ISO 5.5 / 25 / 50 Joule universal, digital Notch cutting machine Tensile impact Dynstat Manual notch cutter Automation Instrumentation Instrumented Impact Testing 3

4 Pendulum Impact Testing - Basics There are four pendulum impact tests standardized. There is only a standard for instrumented Charpy tests. (ISO 179 2) Charpy ISO 179, ASTM D 6110 IZOD ISO 180, ASTM D 256 Tensile Impact Here: ISO 8256 method A Dynstat DIN Instrumented Impact Testing 4

5 Pendulum Impact Testing - Basics Charpy is the recommended test method in the ISO standard. Standards: ISO 179 Part 1 and 2 ASTM D 6110 Notched or not notched Evaluate type of break optically ISO standard: always use the biggest possible pendulum hammer only use 10 to 80% of the pendulum hammer s energy capability impact strength normally is measured in kj/m² Instrumented Impact Testing 5

6 Pendulum Impact Testing - Basics The conventional impact strength is measured by the drop height and the mass of the pendulum hammer. E energy m mass of the pendulum hammer h height g acceleration of gravity (on earth 9,81 m/s²) E 1 = m g h 1 E 2 = m g h 2 h 1 h 2 E specimen = m g (h 1 h 2 ) Instrumented Impact Testing 6

7 Pendulum Impact Testing - Basics To characterize the material it is important to know the type of break. Standardized types of break: N non-break (no valid result) P partial break H hinge break C complete break N The most frequent type of break within a test series determines the results to be used in the statistics. Instrumented Impact Testing 7

8 Pendulum Impact Testing - Basics There is not result without specimen break! Guidance according ISO standards on how to obtain break 1. The preferred method is to use unnotched specimen 2. if no valid break types can be achieved Use specimen with type 1 notch (0.25 mm) 3. If still no valid break types can be achieved Use specimen with type 3 notch (0.1 mm) 4. If still no valid break types can be achieved Use the tensile-impact method Instrumented Impact Testing 8

9 Agenda Pendulum Impact Testing - Basics Instrumented Impact Testing Tests and Curves Summary Instrumented Impact Testing 9

10 conventional hammer instrumented hammer Instrumented Impact Testing Instrumented pendulum testers of the HIT portfolio capture additional material properties. used in R&D, TS and QA Charpy Izod tensile impact Fracture mechanics Instrumented Impact Testing 10

11 Instrumented Impact Testing The force-travel diagram provides more detailed materials data obtained under high deformation rates. F E s = F s Same energy levels can occur at high material resistance and low deformation or with low resistance and high deformation. Instrumented impact allows to distinguish such situations, while conventional impact can t. E specimen E specimen s E energy F force s travel Instrumented Impact Testing 11

12 Instrumented Impact Testing F M maximum force s M deflection at maximum force F I First impact maximum No contact between pendulum hammer and specimen Instrumented Impact Testing 12

13 Instrumented Impact Testing Zwick developed an automatic recognition of test curve types according to ISO 179 part 2 in collaboration with Borealis. no break partial break tough break brittle break splitter break Type of break can be identified by instrumentation Automatic classification of the statistics by the type of break Safe and reliable test results are obtained even with many operators and in night shifts Problems in test setup and specimen handling become visible and thus also traceable. Hinge break Complete break types Instrumented Impact Testing 13

14 Instrumented Impact Testing How does instrumented pendulum testing work at Zwick? Instrumented Impact Testing 14

15 Instrumented Impact Testing To get the energy you need the deformation of the specimen (s). F E specimen = F s E energy W work (energy) E specimen = F s ds F force s specimen deformation The travel s is not directly measured The following slides show how to calculate the deflection from the force signal. E specimen s Instrumented Impact Testing 15

16 Instrumented Impact Testing The measurement of force can be performed by two different systems: strain gage or piezoelectric Instrumentation strain gage piezo strain gage advantage Light weight high natural frequency hammer not sensitive towards position Acceptable natural frequency disadvantage Sensitive towards position Additional surfaces fin piezo Instrumented Impact Testing 16

17 Instrumented Impact Testing If the natural frequency of the system is too low, the measured signal will be dithered and the test result is not usable. Instrumented Impact Testing 17

18 Instrumented Impact Testing If the resonance frequency of the system is high enough the typical properties of the specimen are clearly visible. Resonance 3 x natural frequency of the specimen Instrumented Impact Testing 18

19 Tests and Curves High enough measurement system frequency Instrumented Impact Testing 19

20 Instrumented Impact Testing The force time function is measured by instrumentation. m F E energy t time F force s travel / deformation m mass Instrumented Impact Testing 20

21 Instrumented Impact Testing The acceleration (a) is directly related to the force signal. The travel (s) can be obtained by double integration of (a). F = m a a = F/m F force (measured) m mass of the pendulum hammer a acceleration v velocity s travel t time Integration Integration Instrumented Impact Testing 21

22 Instrumented Impact Testing The resilience (E ) can be obtained by integration of the forcetravel curve. E energy W work (energy) F force s travel / deformation E specimen = F s ds 4 mm 10 mm a cu or N = E specimen specimen cross section in kj/m²] Instrumented Impact Testing 22

23 Agenda Pendulum Impact Testing - Basics Instrumented Impact Testing Tests and Curves Summary Instrumented Impact Testing 23

24 Tests and Curves F M maximum force s M deflection at maximum force F I Maximum of inertia Contact between pendulum hammer and specimen breaks off. Instrumented Impact Testing 24

25 Tests and Curves 4mm Instrumented Impact Testing 25

26 Tests and Curves Which type of break is shown here? no break Instrumented Impact Testing 26

27 Tests and Curves Which type of break is shown here? brittle break Instrumented Impact Testing 27

28 Tests and Curves Which type of break is shown here? tough break Instrumented Impact Testing 28

29 Tests and Curves Which type of break is shown here? splitter break Instrumented Impact Testing 29

30 Agenda Pendulum Impact Testing - Basics Instrumented Impact Testing Tests and Curves Summary Instrumented Impact Testing 30

31 Summary Zwick s HIT series - a complete product range for impact testing Four different test methods are standardized: Charpy, Izod, tensile-impact and Dynstat. Conventional impact machines determine the resilience as a function of the angle of raise of the pendulum. Only the Charpy method is standardized as an instrumented method, even though other instrumented methods are technically available. (ISO 179 2) Additional information on the material properties can be identified by instrumentation. The type of break can be automatically detected through instrumented tests. Fracture mechanic behavior can be determined Instrumented Impact Testing 31