Fracture Analysis and Failure Mechanism of TA3 Limited Contact-Dynamic Compression Plates
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摘要: 为探究TA3纯钛有限接触动态加压接骨板(LC-DCP)在人体内服役期间发生断裂的失效机制,采用化学成分分析仪、维氏硬度仪、光学显微镜和扫描电镜(SEM)等手段,对7个临床断裂失效的TA3纯钛LC-DCP样品进行了断口形貌分析;建立了TA3纯钛LC-DCP固定股骨干中段横形骨折的三维有限元模型,并采用ANSYS对该模型进行了受力分析. 研究结果表明:7个TA3纯钛LC-DCP样品的材料符合要求,断口均位于接骨板中段螺钉孔处;断口表面均出现疲劳辉纹和二次裂纹,裂纹源区、扩展区和瞬时断裂区的元素组成相同;骨折患者在愈合前下地行走会导致接骨板的最大剪切应力大于TA3材料的屈服强度极限,且最大剪切应力发生在接骨板中段螺钉孔处;TA3纯钛LC-DCP的临床断裂失效主要源于骨折患者在愈合前下地行走导致过载,使得接骨板中段螺钉孔处萌生裂纹,随后承受循环疲劳载荷,最终断裂失效.Abstract: To investigate the fracture mechanism of TA3 pure titanium limited contact-dynamic compression plates (LC-DCP) during service in the body. 7 clinically fractured TA3 pure titanium LC-DCP were collected and sterilized, and their fracture surfaces were examined using chemical composition analyzer, Vickers hardness tester, optical microscope, and scanning electron microscope. A three-dimensional finite element model of middle femoral transverse fracture treated by TA3 pure titanium LC-DCP was established, and then the fracture healing and bone plate stress were analyzed using ANSYS software. The results show that the physical and chemical properties of the 7 LC-DCP are qualified, fracture occurs around the middle screw hole on the bone plates. Fatigue striations and secondary cracks appear on the fracture surface, and the regions of crack initiation, propagation and transient fracture, have same elemental compositions. For the patients walking prematurely, the maximum shear stress of bone plates occurs at the middle screw hole and it exceeds the yield strength of TA3 pure titanium. In sum, the fracture failure of the TA3 pure titanium LC-DCP in body is mainly resulted from patients walking prematurely, at the condition, cracks are initiated at the middle screw hole on the bone plate surface, and fatigue fracture occurs under the action of complex cyclic loading.
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Key words:
- bone plate /
- facture analysis /
- finite element analysis /
- fatigue crack /
- failure analysis
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表 1 股骨和TA3纯钛的材料参数
Table 1. Material parameters of femur and TA3 pure titanium
对象 弹性模量/GPa 泊松比 皮质骨 Ex (纵向)= 18.400
Ey (横向) = 7.000
Ez (径向) = 8.500νxy (xy 面)= 0.120
νyz (yz 面)= 0.370
νxz (xz 面)= 0.140松质骨 1.061 0.225 TA3纯钛 103.400 0.300 表 2 TA3纯钛LC-DCP的化学成分(质量分数)
Table 2. Chemical compositions of TA3 pure titanium LC-DCP (mass)
% 样品编号 C N O H Fe 1# 0.0016 0.0067 0.2072 0.0012 0.2081 2# 0.0030 0.0129 0.1637 0.0009 0.0701 3# 0.0023 0.0151 0.2093 0.0011 0.1673 4# 0.0106 0.0116 0.1196 0.0012 0.2543 5# 0.0116 0.0068 0.1879 0.0005 0.2008 6# 0.0020 0.0197 0.2186 0.0001 0.1798 7# 0.0101 0.0161 0.2721 0.0069 0.2500 标准值 ≤0.0800 ≤0.0500 ≤0.3500 ≤0.0150 ≤0.3000 表 3 TA3纯钛DCP接骨板的维氏硬度(HV10)
Table 3. Vickers hardness of TA3 pure titanium DCP bone plates (HV10)
样品编号 断口 基体 标准值 均值 最大偏差 均值 最大偏差 1# 262 15 260 11 ≥ 150 2# 270 18 273 16 3# 243 9 248 10 4# 273 13 265 10 5# 225 16 230 18 6# 271 13 266 12 7# 220 15 225 13 表 4 TA3纯钛LC-DCP接骨板的平均晶粒度
Table 4. Averaged grain size of TA3 pure titanium LC-DCP bone plates
样品编号 断口处 基体处 标准值 1# 7.18 7.10 ≥ 5.00 2# 9.21 9.20 3# 8.66 8.59 4# 8.48 8.37 5# 7.00 6.95 6# 9.24 9.21 7# 9.67 9.60 表 5 术后4周、8周中间骨痂的材料属性
Table 5. Calculated material properties of the callus 4 and 8 weeks after surgery
骨折间
隙/mm4 周皮质骨 4 周松质骨 8 周皮质骨 8 周松质骨 弹性模
量/MPa愈合效
率/%弹性模
量/MPa愈合效
率/%弹性模
量/MPa愈合效
率/%弹性模
量/MPa愈合效
率/%1 0.06 9.54 0 0 3.79 13.35 0 0 2 0.17 83.90 0.01 100.00 25.60 91.36 1.65 100.00 3 0.19 100.00 0.01 100.00 28.00 100.00 1.65 100.00 4 0.19 99.57 0.01 100.00 27.22 97.20 1.65 100.00 5 0.18 90.06 0.01 100.00 24.91 88.89 1.65 100.00 6 0.16 75.98 0.01 100.00 20.89 74.46 1.65 100.00 7 0.14 63.14 0.01 86.71 17.25 61.40 1.36 82.60 8 0.12 51.76 0.01 57.11 14.14 50.27 0.87 52.89 9 0.11 41.35 0.01 28.30 11.06 39.24 0.38 22.89 10 0.09 30.31 0 3.98 8.17 28.94 0.04 2.09 -
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