VIII th International Workshop NDT In Progress

Transcription

1 VIII th International Workshop NDT In Progress October 12 14, 215, Prague, Czech Republic Daniel TOKAR Zdenek PREVOROVSKY Institute of Thermomechanics Academy of Sciences of the Czech Republic Dolejskova 142/5 Prague, Czech Republic

2 Outline What is this presentation about 1. Introduction to mechanical behaviour of the human skin 2. Motivation for the research and background 3. Measuring method description multi-directional flexible circular probe measuring system: composition, calibration anisotropy, NEWS, Time-Reversal 4. Results human skin in-vivo carbon-fabric fiber composite (CFRP) 5. Conclusion 6. Perspective and future work 2/16

3 Introduction Human skin s mechanical behaviour Human skin anatomical structure: epidermis dermis elastin and collagen fibres hypodermis fatty tissue Human skin mechanical properties: nonlinear stress-strain diagram viscoelasticity, mechanical hysteresis anisotropy Langer s lines HENDRIKS, F. M.: Mechanical behaviour of human epidermal and dermal layers in vivo. Proefschrift. Eindhoven: Technische Universiteit Eindhoven, 25. ISBN X. 3/16

4 Introduction Motivation for the research and background Biological aspects of the skin are well known, mechanical behavior is not yet fully investigated Skin mechanical properties are affected by environmental and other conditions: age, temperature, humidity, UV radiation, etc. Measurement of human skin anisotropy development of fast and easy to use method for local anisotropy investigation in-vivo contribution to knowledge of global skin properties plastic surgery implants localization Nonlinear methods investigation of changes in mechanical properties of the skin related to environmental conditions, skin diseases, ageing, etc. 4/16

5 Methods System for local anisotropy evaluation Multi-directional flexible circular ultrasonic probe log Impedance Z (k ) f s = 28 khz f p = 32 khz Frequency (khz) 5/16

6 Methods System for local anisotropy evaluation Measuring system: AWG + power-amplifier, high-speed digitizer + preamplifiers (2 db gain, HP 2 khz), PXIe, 8-ch multiplexer TESTED MATERIAL i = 1 8-ch MULTIPLEXER MULTI-DIRECTIONAL ULTRASONIC PROBE AMPLIFIERS PXIe BUS NI PXIe 8-ch PXIe DIGITIZER PXIe AWG 6/16

7 Methods System for local anisotropy evaluation System s calibration on isotropic polymethylmethacrylate sample Ultrasound propagation velocity (m s -1 ) Probe orientation in x axis Probe orientation in y axis signal averaging threshold-value detection Amplitude (mv) Time ( s) arrival-time 7/16

8 Results Forearm skin anisotropy measurement Volunteer: female, 25 years, skin thickness 1.3 mm AWG output - Amplitude (V) Time( s) Ar = c max c min c 1 (%) 8/16

9 Results Forearm skin anisotropy measurement Volunteer: male, 28 years, skin thickness 1.9 mm AWG output - Amplitude (V) Time( s) Ar = c max c min c 1 (%) 9/16

10 Results Carbon fabric-reinforced plastic - composite Intact specimen Damaged specimen 1/16

11 Results NEWS methods applied on the forearm skin f / 2 f Harmonics ratio ( ) FFT (db) 3 f / 2 f (polynomial) Sine-train, f = 38 khz Frequency(kHz) Fundamental frequency f f / 2 f f / 2 f (polynomial) Time( s) Harmonics ratio ( ) FFT (db) AWG output - Amplitude (V) Frequency(kHz) Fundamental frequency f 11/16

12 Results NEWS methods applied on CFRP composite 1 3 f / 2 f -4 3 f / 2 f (polynomial).9-6 Intact.8 Harmonics ratio ( ) FFT (db) Sine-train, f = 38 khz Fundamental frequency f 9 Frequency(kHz) f / 2 f 3 f / 2 f (polynomial) Time( s) Harmonics ratio ( ) FFT (db) AWG output - Amplitude (V) Damaged Frequency(kHz) Fundamental frequency f /16

13 Results Chirp-coded TRA applied on the forearm skin Volunteer: female, 25 years, skin thickness 1.3 mm 1 Linearly swept sine, (2 4) khz AWG output - Amplitude (V) Time( s) Along the longitudinal axis Across the longitudinal axis Normalized unit ( ) Time ( s) 13/16

14 Results Chirp-coded TRA applied on the forearm skin Volunteer: male, 28 years, skin thickness 1.9 mm 1 Linearly swept sine, (2 4) khz AWG output - Amplitude (V) Time( s).8.6 Along the longitudinal axis Across the longitudinal axis Normalized unit ( ) Time ( s) 14/16

15 Results TRA reconstruction during mechanical loading Energy (focus) Energy (side-lobes) 15/16

16 Summary Conclusion and future work New measurement method for local anisotropy evaluation of various biological and industrial materials; tested on human skin in-vivo, carbon fabric-fiber composite, and polymethylmethacrylate Anisotropy diagrams for the forearm skin corresponds with Langer s line orientation but embody individual differences useful in plastic surgery Sufficiently accurate results: calculated variation coefficients < 1 % Results of NEWS and TRA methods applied on the skin show differences in the nonlinear signatures related to the direction of propagation through the skin (orientation of collagen fibers) Sensitive TRA method is promising for detection of changes in the mechanical behavior caused by tensile loading and external environmental influences Presented results and approaches should help to comprehend complex mechanical behavior of the human skin 16/16

17 VIII th International Workshop NDT In Progress October 12 14, 215, Prague, Czech Republic Daniel TOKAR Zdenek PREVOROVSKY