Study on Optimal Design of PMMA/CNT Microcellular Density Gradient Materials for Energy Absorption

doi:10.19491/j.issn.1001-9278.2021.05.006

Abstract

Abstract:

Compared to homogeneous foams， the density-graded foams have significant advantages such as lighter weight and better energy-absorption efficiency. To investigate the influence factors of the energy-absorption characteristics of density-graded foams and optimize their design， this paper focused on a microcellular energy-absorption foam based on poly（me-thyl methacrylate） and carbon nanotubes. A graded foam model was established with an equal interlayer density difference. Through the nonlinear phenomenological constitutive model fitting of a constitutive equation under the quasi-static compre-ssion， the distribution features and corresponding advantages and disadvantages of energy absorption efficiency of the foam model were calculated under different loads. The influence rules of interlayer density difference， upper and lower density differences and thickness graded rule of foam layer on the energy absorption efficiency of the foam model were studied. The results indicated that the foams with interlayer density differences of 25 kg/m³ and 50 kg/m³ exhibited a better energy absorption capability. With reducing the upper and lower density difference， the peak of energy absorption efficiency increased， but the energy absorption efficiency at lower loads decreased. The peak of energy absorption efficiency increased with an increase in the thickness of the foam layers， whose density was closer to the apparent density. Based on the experimental results， an optimal graded foam model was established， leading to a peak value of 0.326 for energy absorption efficiency as well as a better energy absorption capability than homogeneous foam within the loading range of 15 MPa. These results can provide an important guiding significance for the design of density gradient materials for energy absorption.

Key words: graded foam, carbon nanotube, poly（methyl methacrylate）, composite, microcellular foam, quasi-static compression, energy-absorption performance

CLC Number:

TQ325.7

ZHANG Yijun, ZHANG Ruizhi, GUO Chengcheng, SHEN Qiang, LUO Guoqiang. Study on Optimal Design of PMMA/CNT Microcellular Density Gradient Materials for Energy Absorption[J]. China Plastics, 2021, 35(5): 32-39.

Figures/Tables 11

Fig.1. The microstructure of the PMMA/CNT nanocomposites foams foamed at different temperature

参数	表达式和值
A	$5.61 × 10 - 2 ρ ? - ? 7.840 ? 8$
B	12
C	$8.430 ? 8 × 10 - 6 ρ 2 + 2.873 × 10 - 3 ρ - 4.272 ? 9$
σ	50
β	50
γ	$- 10.837 × 10 - 6 ρ 2 + 2.194 × 10 - 3 ρ - 7.012 ? 8$

参数	表达式和值
A	$5.61 × 10 - 2 ρ ? - ? 7.840 ? 8$
B	12
C	$8.430 ? 8 × 10 - 6 ρ 2 + 2.873 × 10 - 3 ρ - 4.272 ? 9$
σ	50
β	50
γ	$- 10.837 × 10 - 6 ρ 2 + 2.194 × 10 - 3 ρ - 7.012 ? 8$

Tab.1. Mathematical expressions and values of the parameters

Fig.2. Schematic of the discretely standard graded foam

Fig.3. Comparison of stress?strain curves and energy absorption efficiency curves of standard graded foam with homogeneous foam

Fig.4. Comparison of stress strain curves and energy absorption efficiency curves of different Δρ

Fig.5. Comparison of stress strain curves and energy absorption efficiency curves of different density span

Fig.6. The model map of Dumbbell form and Spindle form

单层密度/kg·m^-3	泡沫模型单层厚度/mm
单层密度/kg·m^-3	标准梯度	哑铃形	纺锤形
200	2.5	4	1
250	2.5	3	2
300	2.5	2	3
350	2.5	1	4
400	2.5	1	4
450	2.5	2	3
500	2.5	3	2
550	2.5	4	1

Tab.2. The layer thickness parameters of Dumbbell foam and Spindle foam

Fig.7. Comparison of stress strain curves and energy absorption efficiency curves of Dumbbell foam and Spindle foam

Fig.8. Schematic of the optimized graded foam model

Fig.9. Energy absorption efficiency curves of the optimized graded foam model

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