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研究生:簡絲男
論文名稱:鑄態球狀石墨鑄鐵共振破壞特性之探討
論文名稱(外文):A Study on the Resonant Vibration Characteristic of As-Cast Spheroidal Graphite Cast Iron
指導教授:陳立輝陳立輝引用關係呂傳盛呂傳盛引用關係
指導教授(外文):L. H. ChenT. S. Lui
學位類別:碩士
校院名稱:國立成功大學
系所名稱:材料科學及工程學系
學門:工程學門
學類:材料工程學類
論文種類:學術論文
論文出版年:1999
畢業學年度:87
語文別:中文
論文頁數:65
中文關鍵詞:共振球墨鑄鐵鑄鐵
外文關鍵詞:resonantspheroidal graphite cast ironcast iron
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球墨鑄鐵應用於交通器材之零件時,難免會遭受到共振破壞的問題,這些零件中有許多是在鑄態未經熱處理就被使用,因此對於鑄態球墨鑄鐵的共振特性有必要做一系統性之探討。此外,共振之原理,可應用於精密鑄造上,將澆鑄後所得之工件與澆道振離。本研究選用3.6w%C 2.9w%Si的鑄態球墨鑄鐵,澆鑄過程中,待熔湯凝固後以不同速率之降溫處理,以取得不同微觀組織(波來鐵含量)之試料,以探討微觀組織組織對共振特性之影響。
共振破壞過程中,末端偏移量對振動次數的關係可分為三階段:初期末端偏移量保持一安定值,而在圖形中呈一平台區;後來試片末端偏移量隨著動次數增加而急速下降;最後因較低之末端偏移量使得試片受較小之力,而成偏移量較低之另一平台區。各試料中,圖形的變化與裂紋生成及傳播有關。大部分的裂紋起源於球狀石墨與基地之界面,而也有少數裂紋起源於介在物;裂紋起源後開始向基地傳播,微小之裂紋互相之間開始串連;上述裂紋起源與初期串連兩階段中試片之末端偏移量處於安定狀態的初期平台區。當許多裂紋串連而產生主裂紋後,主裂紋快速向試料中央傳播,導致系統有效彈性係數改變,此時試片末端偏移量會因為已偏離了共振頻率而急速下降,當試片末端偏移量降至一定程度後,試片因受力減小使得裂紋傳播速率較緩慢,會在低偏移量再度呈現另一平台區。
實驗結果確認波來鐵含量的增加會使共振頻率些微提高;制振性亦會隨著波來鐵含量增加而變差,使得處於共振狀態時,波來鐵含量愈高者其末端偏移量愈大。裂紋在波來鐵基地內之傳播路徑有兩種:有時沿著薄板平行方向傳播;有時垂直切過薄板而傳播。裂紋於肥粒鐵基地傳播時大部份是以穿晶方式前進,以SEM觀察破斷面確認,只有牛眼組織中球墨旁邊發現少數的沿晶破斷面產生。
裂紋傳播時會在肥粒鐵晶界、波來鐵與肥粒鐵之界面及波來鐵層狀方向改變處產生裂紋轉折或分歧,因而分散降低裂紋傳播的驅動力。雖然波來鐵含量增加會造成共振狀態時末端偏移量提高,但裂紋在波來鐵基地中具較高的轉折度與分歧度,且波來鐵對裂紋傳播具有阻抗效用,因此波來鐵含量增加時有助於共振壽命的提高。
Spheroidal graphite (SG) cast iron has been used in many automobile components. During application, resonant vibration may occur and cause failure. A lot of these automobile components are used in as-cast condition, so systematic exploration of the resonant vibration characteristics of as-cast SG cast iron is necessary. In addition, the resonant vibration test can also be applied to separate the sprue and workpiece in investment casting. The as-cast SG cast iron of 3.6wt%C-2.9wt%Si was used in this study. By varying the cooling rate after solidification, different matrix structures (pearlite components) were available, which aimed to study the effect of matrix structures on resonant vibration characteristics.
During resonant vibration, the variation of deflection amplitude vs. vibration cycles could be divided into three stage. Firstly, the deflection amplitude maintain about constant for a certain period of vibration cycles (stage I). Then, the deflection amplitude decreases significantly with increasing vibration cycles. In the third stage, the deflection amplitude maintains about constant again, but significantly lower than the deflection amplitude of stage I. The above mentioned feature of three-stages behavior is related to the result of crack initiation and propagation. Mostly, microcracks initiate from the interface between graphite nodules and matrix, and fewer microcracks initiated from the inclusions in eutectic cell wall. Microcracks propagated to link each other and finally become major cracks with increasing vibration cycles. The process of crack initiation and linking were proceeding during the stage I period. After the formation of major cracks, the major cracks propagate through the thickness direction, then the effectic elastic modulus of specimen was reduced. Due to the drop of elastic modulus, the deflection amplitude decreased significantly as shown the feature of "stage II". In stage 3, the lower of deflection amplitude and cracking rate makes another plateau region.
The experimental results showed that the increment of pearlite contents would slightly increase the resonant frequency of specimen. The damping capacity decreases with increasing pearlite content and so does deflection amplitude. After initiation, the cracks propagated in. The cracks propagated in the pearlite matrix along two paths. Sometimes it goes along the cementite platelets and sometimes through cementite platelets. Mostly, cracks propagated transgranularly in ferrite matrix, but fewer intergranular fracture near the bull''s-eye region is also observed by SEM.
As the crack extends, the deflection and brunching occur on the grain boundaries of ferrite, the interface between ferrite and pearlite and the cementite platelets with different orientation. Thus, the driving force for crack propagation is reduced. Although the pearlite content can cause the deflection amplitude under resonant, to increase the crack propagates in the pearlite with higher degree of deflection and branching and the pearlite can retard crack extension. Therefore, the resonant vibration life can be improved with increasing the pearlite content.
總目錄
中文摘要I
英文摘要III
總目錄V
圖表目錄VIII
第一章 前言1
第一章 文獻回顧3
2-1 冶金因素對鑄態球墨鑄鐵之影響3
2-2 共振頻率4
2-3 制振性4
2-4 共振破壞6
2-5 裂紋之生成與傳播6
2-5.1裂紋的起源6
2-5.2裂紋傳播路徑7
2-5.3疲勞壽命與微觀組織8
第三章 實驗方法12
3-1 材料的準備12
3-2 微觀組織定量化12
3-3 制振性的量測13
3-4 共振實驗13
3-5 裂紋與微觀組織觀察14
第四章 實驗結果20
4-1 微觀組織之定量化觀察20
4-2 共振狀態與非共振狀態之比較20
4-3 出力值對共振特性之影響21
4-4 微觀組織對共振特性之影響22
4-4.1 基地組織對共振頻率與偏移量影響22
4-4.2 基地組織對制振性影響22
4-4.3 基地組織對共振壽命之影響23
4-5 裂紋之生成與傳播.24
4-5.1 裂紋起源25
4-5.2 裂紋之傳播過程25
4-5.3 波來鐵對裂紋之影響26
4-5.4 裂紋轉折及裂紋分歧27
4-6 試料之破斷面觀察27
第五章 討論53
5-1 微觀組織53
5-2 制振性53
5-3 裂紋之起源與傳播54
5-3.1 裂紋之起源55
5-3.2裂紋對振動次數與偏移量關係之影響55
5-4 基地組織對裂紋傳播之影響55
5-4.1 裂紋傳播對波來鐵之依存性56
5-4.2 裂紋轉折度及裂紋分歧度56
5-5 波來鐵含量對共振壽命之影響57
第六章 結論59
第七章 參考文獻61
圖表目錄
圖2-1 變形能量中供給之能量與回復的能量之狀態10
圖2-2 自由衰減曲線10
表3-1 本研究所使用球墨鑄鐵的化學成份(wt%)15
圖3-1 實驗流程示意圖16
圖3-2 Y型砂模的形狀與尺寸17
圖3-3 試片尺寸與振動試驗機示意圖18
圖3-4 計算裂紋轉折度及裂紋分歧度之示意圖19
表4-1 微觀組織之定量化29
表4-2 以2G、26Hz所測得不同波來鐵含量之衰減率(Δ)29
表4-3 2vol%波來鐵中出力值對衰減率(Δ)之影響29
表4-4 不同波來鐵含量之裂紋轉折度及裂紋分歧度29
圖4-1 不同冷卻速率下所得到之不同波來鐵含量試料30
圖4-2 各部位之EDS分析31
圖4-3 末端偏移量對振動頻率之依存性(2G)32
圖4-4 不同振動頻率對振動次數對末端偏移量之比較32
圖4-5 同一試料不同G值之振動次數對末端偏移量關係33
圖4-6 出力值對共振壽命之影響34
圖4-7 四組不同波來鐵含量以2G所求得之末端偏移量對振動頻率之依存性35
圖4-8 以2vol %波來鐵之試料為例,末端偏移量之衰減36
圖4-9 不同試料末端偏移量對振動次數之關係37
圖4-10 波來鐵含量對共振壽命之影響38
圖4-11 不同試料的末端偏移量對振動次數之關係比較(相同起使偏移量)。39
圖4-12 波來鐵含量對共振壽命之影響(相同起始偏移量)40
圖4-13 波來鐵含量70vol%試料之表面裂紋傳播觀察41
圖4-14 波來鐵含量5vol%試料之表面裂紋傳播觀察42
圖4-15 裂紋之起源43
圖4-16 裂紋傳播與球墨之關係44
圖4-17 裂紋傳播與肥粒鐵晶界之關係45
圖4-18 裂紋傳播對波來鐵無選擇性46
圖4-19 裂紋傳播與波來鐵層狀組織之關係47
圖4-20 裂紋傳播與波來鐵及肥粒鐵界面之關係48
圖4-21 破斷面之觀察(2vol%波來鐵)49
圖4-22 破斷面之觀察(5vol%波來鐵)50
圖4-23 破斷面之觀察(50vol%波來鐵)51
圖4-24 破斷面之觀察(70vol%波來鐵)52
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