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研究生：	黃宇祥 Huang, Yu-Hsiang
論文名稱：	材料的時間相依力學性質之研究 Time-dependent mechanical properties of materials: case studies of two metals and polymeric foam
指導教授：	王雲哲
學位類別：	碩士 Master
系所名稱：	工學院 - 土木工程學系 Department of Civil Engineering
論文出版年：	2013
畢業學年度：	101
語文別：	英文
論文頁數：	114
中文關鍵詞：	黏彈性質、鑄鐵、Al7075-T73鋁合金、高分子泡沫材料、潛變、塑性
外文關鍵詞：	Viscoelastic properties, Cast iron, Al 7075-T73 aluminum alloy, Polymer foam, Creep, Plasticity
相關次數：	點閱：72 下載：0
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本論文探討材料的時間相依之力學性質與行為，以線黏彈性理論為基礎，研究潛變、應力鬆弛、動態模數與正切消散模數，此外亦探討金屬材料之塑性行為。本論文所研究的材料包含：發泡高分子材料、FC25灰口鑄鐵、及Al7075鋁合金。

高分子泡沫材料是一種輕質材料，適用於航空航天應用的承重結構或降噪泡沫材料，其微觀結構是由許多細小的骨幹組成的，使它擁有其獨特的機械性能。在這項研究中，我們採用兩種孔洞尺寸、為幾百微米到一毫米的商業聚氨酯泡沫體進行單軸壓縮研究、潛變及應力鬆弛，研究其正切消散模數和動態正弦波加載的儲能模量，了解泡沫材料的性能，研究發現，彈性模量和降服應力會與加載速率有關。在大孔徑泡沫我們可以觀察到應力平原帶，泡沫材料當其變形越大的時候，因為被壓擠後變得越緻密，越像一塊完整無孔洞的材料，加載速率的影響就較不明顯。

FC25灰口鑄鐵和含鎳、鈷、碳、矽、錳的低熱膨脹鑄鐵，對這兩種鑄鐵進行室溫下潛變行為研究。這兩個鑄鐵皆經過-190℃的超深冷處理，來研究此兩種鑄鐵會受什麼影響。低溫處理目前被當作提高材料穩定度的方法，在此實驗想藉此觀察低溫處裡後之鑄鐵的常溫潛變行為是否有所改善。我們發現這兩個物種具有相似的晶粒尺寸，約為100微米。從納米壓痕的數據結果來看，兩種鑄鐵的楊氏模量為 170 GPa，硬度約 5 GPa。從室溫下的潛變2天的數據，可以發現未經處理的試體，低熱膨脹的鑄鐵比FC25更穩定、潛變較小。深冷處理後，FC25之潛變顯示略有改善，但低熱膨脹並沒有明顯的改善。從2週的數據來看，對於FC25試體來說，低溫處理反而造成潛變量增加，可能材料在深冷處理過程中，因內部含碳量過高、熱膨脹係數不均勻，導致產生許多微裂紋而使材料的強度下降。

在關於Al7075鋁合金的塑性行為研究中，探討中空圓形板，在外緣完全幾何束制下，因加溫導致的塑性行為，殘餘應力藉由奈米壓痕實驗之硬度量測而決定。此外，Al7075鋁合金在常溫下的張力與四點彎曲行為亦加以討論，獲得常溫下完全的材料彈塑性質，用以配合理論，預測中空圓形板之塑性行為。

This research studies the time-dependent material properties in the context of the linear viscoelasticity and plasticity theory. Creep, stress relaxation, dynamic modulus and loss tangent of polymer foam were studied. Creep of FC25 gray cast iron and nickel-rich cast iron was conducted to test material stability. Plastic deformation of Al 7075-T73 aluminum alloy under tension and four-point bending was performed.

Polymer foam is a lightweight material suitable for vibration isolation and noise reduction. The microstructure of the foam, which is constructed with cell ribs, allows its unique mechanical properties. In this work, commercial polyurethane foams with two pore sizes, a few hundred microns and 1 mm, were subjected to uniaxial compression at various strain rates, including creep and relaxation, as well as dynamic sinusoidal loading for studying their loss tangent and storage modulus, to study the material properties of the foams. It is found that modulus and yield stresses are functions of loading rate. For large pore size foam, stress plateau can be observed. Rate-dependent behavior of foam becomes less rate sensitive when under large deformation due to densification.

The FC25 grey cast iron and a low-thermal-expansion (nickel-rich) cast iron, containing {Ni}, {Co}, {C}, {Si}, {Mn}, are studied for their room temperature creep behavior. Both species are treated at -190℃ to study the effects of cryogenic processing. The cryogenic processes are intended to improve the material stability in terms of being insensitive to room temperature creep. Our results show both species have similar grain size on the order of 100 microns. From nanoindentation, the Young’s modulus and hardness are about 170 GPa and 5 GPa, respectively, for both species. From the room-temperature creep data, it is found that for untreated specimens, the low-thermal-expansion specimen is more stable than FC25 specimen. After cryogenic treatment, the FC25 shows a slight improvement to against creep, but the low-thermal-expansion ones do not show clear trends. From two weeks of data, for FC25 specimens, the creep after the cryogenic treatment is increase, possibly material in cryogenic treatment process, due to the internal carbon content is too high, the thermal expansion coefficient uneven, resulting in many micro-cracks to decrease the strength of the material.

As for the Al 7075 aluminum alloy, the plastic behavior of the alloy is studied by thermal loading on an annular disc with full displacement boundary conditions on the outer rim. The hardness of the plate at different locations were determined by nanoindentation. In addition, the stress-strain curves from the uniaxial and four-point bending tests were experimentally obtained to serve as fundamental material properties for future modeling work.

CHINESE ABSTRACT . . . . . . . . .. . . . . . . i
ABSTRACT . . . . . . . . . . . . . . . .. . . . iii
ACKNOWLEDGMENTS . . . . . . . . . . . . . . . .. v
LIST OF TABLES . . . . . . . . . . . . . . . . . x
LIST OF FIGURES . . . . . . . . . . .. . . . . . xii
NOMENCLATURE . . . . . . . . . . . . . . . . . . xvii
Introduction . . . . . . . . . . . . . . . . . 1
1 Goals and motivation . . . . . .. . . . .. . 1
2 Literature review . . . . . . . . . . . . .. 2
2.1 Foam . . . . . . . . . . . . . . . . . . . 2
2.2 Cast iron . . . . . . . . . . . . . .. . . 2
2.3 Aluminum . . . . . . . . . . . . . . . . . 2
3 Outline of this thesis . . . . . . . . . .. .2
Theoretical . . . . . . . . . . . . . . .. . . 4
1 Viscoelasticity . . . . . . . . . . . . . .. 4
1.1 Creep . . . . . . . . . . . . . . . . .. . 4
1.2 Stress relaxation . . . . . . . . . . .  . 5
2 Standard linear solid . . . . . . . . . . . .7
2.1 Dynamic response . . . . . . . . . . . .  .15
2.2 Biot theory . . . . . . . . . .  . . . . . 16
2.3 The loss tangent from moduli . . . . . ..  19
3 Theory of measuring strain . . . . . . . . . 20
3.1 Electrical resistance strain gages . . . . 20
3.2 Strain gage circuit . . . . . . .. . . . . 21
4 Plasticity . . . . . . . . . . . . . . . . . 26
Experimental . . . . . . . . . . . . . . . . . 28
1 Sample description . . . . . . . . . . . . . 28
1.1 Foam . . . . . . . . . . . . . . . . . . . 28
1.2 Cast iron . . . . . . . . . .. . . . . . . 28
1.3 Al 7075-T73 . . . . . . . . . . .  . . . . 32
2 Machine description . . . . . . . . . . .  . 32
3 Strain measurement . . . . . . . . . ... . . 36
4 Uniaxial test . . . . . . . . .  . . . . . . 37
4.1 Foam . . . . . . . . . . .  . . . . . . . .37
4.2 Cast iron . . . . . . . . .  . . . . . . . 40
4.3 Al 7075-T73 . . . . . . . .. . . . . .. . .40
5 4 point bending test . . .. . . . . . . . . .40
6 Thermal loading test . . . .  . . . . . . . .46
Results and Discussion . . . .  . . . . . . . .49
1 Foam . . . . . . . . . . . . . . . . . . . . 49
1.1 Different strain rate . . . . .. . . . . . 49
1.2 Stress relaxation . . . . .. . . . . . . . 58
1.3 Creep . . . . . . . . . . . . . . . . .. . 58
1.4 Dynamic response . . . . . . . . . . . . . 62
2 Cast iron . . . . . . . .. . . . . . . . . . 66
2.1 Tensile test . . . . . . . . . . . . . . . 66
2.2 Creep . . . . . . .. . . . . . . . . . . . 66
3 Al 7075-T73 . . . . . .  . . . . . . . . . . 72
3.1 Tensile test . . . . . .. . . . . . . . . .72
3.2 4 point bending . . . . . .. . . . . . . . 72
3.3 Thermal loading test . . . . .. . . . . . .72
Conclusions and Future Work . . . . . .. . . . 81
1 Conclusions . . . . .  . . . . . . . . . . . 81
2 Future Work . . . . . .  . . . . . . . . . . 82
LIST OF REFERENCES . . . . . . . ..  . . . . . . 84
APPENDICES
Appendix A: Detailed data for cast iron . .. . .  86
Appendix B: Experiments done in the past .  . . . 96
Appendix C: Presentation slide . . . .  . . . . . 102
VITA . . . . .  . . . . . . . . . . . . . . . . . 112
Index . . . . . . . . . . . . . . . . ..  . . . . 113
                                    

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校內：2018-08-27公開
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