Influence of fused deposition process parameters on static and dynamic mechanical properties of thermoplastic polyurethane elastomer

doi:10.19491/j.issn.1001-9278.2022.05.006

Abstract

Abstract:

To explore the static and dynamic mechanical properties of thermoplastic polyurethane elastomer prepared through the fused deposition modeling process as well as the influence of process parameters on the mechanical properties， the mechanical properties of thermoplastic polyurethane elastomer under a quasi?static loading of 0.01 s^-1 and a dynamic loading of 1 000 s^-1 were evaluated at three printing speeds of 10， 40 and 70 mm/s and three nozzle temperatures of 200， 220， and 240 °C using a universal material testing machine and a split Hopkinson pressure bar （SHPB） experimental apparatus. The process parameters were also optimized. Furthermore， the stress?strain sample space data were further obtained in a wide strain?rate range of 0.001~2 500 s^-1. The results indicated that a nozzle temperature of 220 °C and a printing speed of 40 mm/s were the optimal process parameters under the quasi?static and dynamic loadings. The specimens had a strain?rate effect under both the quasi?static and the dynamic conditions， exhibiting significant hyper?elastic characteristics under the quasi?static condition. Using a viscoelastic constitutive model of the material combined with the ZWT （Zhu?Wang?Tang） equation under the dynamic condition， the fitted curves of the model were in good agreement with the experimental curves. The specimens showed an obvious "micro?phase separation" under the optimal process parameters.

Key words: thermoplastic polyurethane elastomer, fused deposition modeling, split Hopkinson pressure bar, strain rate

CLC Number:

TQ323.8

LEI Jingfa, SHEN Qiang, LIU Tao, SUN Hong, YIN Zhiqiang. Influence of fused deposition process parameters on static and dynamic mechanical properties of thermoplastic polyurethane elastomer[J]. China Plastics, 2022, 36(5): 29-35.

Figures/Tables 16

Fig.1. Schematic diagram for molecular structure of TPU

Fig.2. Schematic diagram of FDM equipment

Fig.3. Photo of quasi?static and dynamic specimens

Fig.4. Split Hopkinson pressure bar device

Fig.5. Dynamic compression raw wave form and stress balance diagram of TPU

Fig.6. Quasi?static stress?strain curves of TPU prepared at different print speed and print head temperature

打印速率/mm·s^-1	喷头温度/℃
打印速率/mm·s^-1	200	220	240
10	9.44	24.69	25.37
40	13.93	37.71	32.50
70	11.96	25.94	28.26

Tab.1. Effect of FDM process parameters on modulus of elasticity of the specimens

Fig.7. Quasi?static engineering stress?strain curves of TPU at different strain rates

Fig.8. Dynamic stress?strain curves of TPU prepared at different print speed and print head temperature

喷头温度/℃	打印速率/mm·s^-1	弹性模量/GPa	屈服应力/MPa
200	10	283.5	11.53
	40	442.0	11.83
	70	212.0	8.57
220	10	470.0	17.88
	40	484.5	18.26
	70	433.0	16.38
240	10	368.2	14.57
	40	449.5	18.15
	70	348.1	13.89

Tab.2. Effect of FDM process parameters on modulus of elasticity and yield stress of the specimens

Fig.9. Dynamic engineering stress?strain curves of TPU at different strain rates

Fig.10. Schematic diagram of ZWT model structure

应变率/ s^-1	E₀/MPa	E₁/MPa	α/MPa	β/MPa	E₂/MPa	θ/μs	R²/%
1 200	-30 600	206 500	14.3	-3531	10 130	-19	98.75
1 800	730	-599	-71.6	-776	55	193	98.69
2 100	-1 281	1 142	209.8	-1 055	290	-178	98.55
2 500	-30 980	30 600	271.4	-1 265	517	-9.49×10^-4	97.99

Tab.3. ZWT model fitting parameter values

Fig.11. Comparison of ZWT model fitting curves and experimental data

Fig.12. SEM images of surface of specimens prepared at different nozzle temperatures and printing speed

Fig.13. SEM image of surface of specimen prepared using optimized process parameters

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