【作者】 徐根；

【导师】 陈枫；

【作者基本信息】 中南大学 ， 工程力学， 2009， 博士

【摘要】 聚晶金刚石复合片(Polycrystalline Diamond Compact,简称PDC)钻头因具有极高的耐磨性、抗冲击韧性以及锐利的切削刃,在地质和石油钻探中受到了广泛的应用。但目前国内外油田上所使用的复合片有80%的非正常失效断裂是由于PDC的残余应力致裂及界面结构问题引起的,热残余应力是造成PDC非正常失效的主要因素。针对上述问题,结合博士点基金项目“油田钻探用金刚石复合片热残余应力致裂与止裂研究”(20070533113),本文采用理论分析、数值计算、实验研究和现场测试与应用相结合的方法,对油田钻探用PDC热残余应力及界面结构优化问题进行了系统深入的研究。主要研究内容如下：(1)针对金刚石与粘结金属之间的界面结合问题,对PDC复合机理以及复合机理、合成技术对界面强度的影响作了深入系统的研究,这为PDC残余应力、界面结构等的研究提供了先决条件。(2)根据PDC合成过程中的热力学规律及弹性理论,建立了平界面结构PDC热残余应力理论模型,推导出复合材料界面剪应力和金刚石层内正应力的理论计算公式,得出对残余应力起决定因素的是金刚石与硬质合金的热膨胀系数差值。通过数值计算方法,对平界面结构PDC热残余应力的大小及分布规律等作了详细的计算和分析,得到了PCD(Polycrystalline Diamond)层厚度与热残余应力、变形之间的相互关系。(3)利用理论分析、有限元数值计算等方法,对PDC界面精细结构及性质、界面反应的控制以及界面结构对力学性能的影响规律作了深入研究,对不同界面结构PDC热残余应力分布规律作了详细的计算和分析,给出了热残余应力与界面结构之间的相互关系,并在此基础上对PDC界面结构进行了优化设计。(4)通过改进的应力释放法、X射线衍射法和Raman光谱法,结合有限元与曲线拟合等数值方法,成功得到了金刚石层表面和界面各点的热残余应力值及其完整的分布规律,且测试结果均与有限元数值计算结果相吻合。本文所用实验方法克服了传统PDC残余应力测量方法中只能测有限几个点的弊端,为PDC刀具的优化设计提供了实验基础,并为准确测试PDC的其他应力,如环向应力等,提供了参考。(5)针对国内PDC耐磨性测试方法中称量法存在较大误差的缺陷,对PDC耐磨性测试方法进行了改进,采用显微镜测量磨耗面边长来计算出磨耗量,从而得到PDC的磨耗比。通过对测量法与称量法测试数据的比较,证明测量法误差小,数据精确,代替天平称重法是完全可行的。另外,对PDC测试部位几何形状对耐磨性测试结果的影响作了实验研究,结果表明对同一片PDC,测试部位几何角度越大,测出的磨耗比越高,测试部位为未经切割的圆弧时,磨耗比最高。本文研究为精确测定PDC耐磨性提供了实验依据。(6)利用Instorn1342材料试验机,采用单轴压缩实验,成功得到了PCD材料的弹性模量、泊松比值。与超声波速率测量法和自由振动频率测量法相比,该方法简单、可靠,测试费用低。利用Instron1342伺服材料试验机以及SHPB装置,成功实现了对PDC从静态→准动态→动态的加载过程,得到了不同加载速率下PDC的侧压强度以及加载速率与侧压强度之间的相关关系,实验结果表明PDC的侧压强度随着加载速率的提高而提高,出现三个最主要阶段的变化：即静态强度、准动态强度以及动态强度(应变率分别为10-6、10-2、和102量级),其中准动态侧压强度为静态侧压强度的7.3倍,而动态侧压强度为静态侧压强度的52.4倍。另外,通过二次破坏性冲击加载的方式,成功得到了PDC试样损伤前后的侧压强度值以及PDC损伤与加载速率、PCD层厚度之间的相关关系。实验结果说明,加载速率越高,PCD层越厚,由冲击载荷引起的PDC内部损伤就越严重。(7)将近十几年来出现的功能梯度材料的概念设计方法引入到PDC的设计中来,将非平面连接技术与梯度过渡技术相结合,综合考虑热残余应力、使用性能及合成工艺三方面因素,设计、研制了高品质的内置过渡层结构PDC,克服了平面结构PDC在残余应力方面所存在的问题,并通过数值计算和实验,证明了该产品的优异性能,成功申请了该产品的实用新型专利。(8)在研究了PDC钻头的碎岩机理以及影响PDC切削齿受力因素的基础上,建立了精确的PDC切削齿受力模型,为PDC钻具工作参数的合理设置提供了依据。同时,对PDC现场使用中的相关问题作了深入探讨,并用内置过渡层结构复合片制作的钻头进行了油田现场钻井实验,取得了相当好的使用效果。本文结合工程中的重大力学问题,综合运用物理、数学、力学理论及方法,结合数值计算工具和先进的实验手段,对油田钻探用PDC热残余应力的分布规律和控制理论及界面结构优化问题进行了深入研究。得到的研究成果对PDC热残余应力的致裂与止裂研究具有重要意义,为有效降低PDC热残余应力,优化PDC界面结构,提高PDC生产合格率及使用寿命,从而降低油田钻探成本,提供了理论与实验依据。更多还原

【Abstract】 Polycrystalline diamond compacts(PDC)bits have gained wide commercial acceptance in oil and gas drilling due to their high rats of penetration, long life and mechanical simplicity. However, eighty percent of PDC failure, according to statistical data, is due to microchipping, gross fracturing and delamination between diamond-layer and the substrate.The thermal residual stress is the main cause leading to PDC failure.Supported by the Doctoral Fund’Study on rupturing and arresting of crack due to thermal residual stresses of polycrystalline diamond compacts for oil drilling’(No.20070533113),the author studied systematically on the residual stresses and interface optimization of polycrystalline diamond compacts for oil drilling.Theoretical and experimental method, as well as finite element method and in-site drilling test were used in the present investigation.The main research contents and results obtained in the dissertation are as follows:The recombination mechanism and sintering technology of PDC have been studied systematically, the relationship between composite mechanism, synthesis technology and interfacial strength is presented, which provides the theoretical basis for researching the residual stresses and interface composition of PDC.The distribution features of residual stresses in plane-interface PDC was studied by theoretical analysis and finite element method. The formulas for calculating the shear stress in complex material interface and the normal stress in polycrystalline diamond (PCD) layer were presented. The obtained results show that the difference of thermal expansion coefficients between PCD and cemented carbide is the main reason for the initiation of residual stresses in PDC.The relationship between the thickness of PCD layer, residual stresses and deformation of PDC is proposed.The property and composition of interface of PDC complex material have been systematically studied.The theory about interface reaction controlling is described. The residual stresses in PDC with different interface structures were calculated using finite element method. The relationship between residual stresses and interface structure is obtained, based on which a new PDC with an optimized interface is proposed.The residual stresses in flat-interface PDC have been measured in laboratories using improved stress-release method, X-Ray diffraction and Raman Spectroscopy method, respectively. The values of residual stresses and it’s distribution on the surface of PCD table were obtained.The tested results were coincident well with that obtained by the numerical method. The shortage existing in traditional experimental method in which only finite points on the PCD table surface can be tested for one specimen has been overcome by the improved method used in the present test. These methods provide an experimental basis for PDC optimum design.The shortcoming of the present method in measuring PDC wear resistance is analyzed. Considering that the weighing of PDC is hard to guarantee the accurate of testing results, the author suggests to measure the length of PDC abrasion facet by microscope and then calculate the abrasion volume instead of weighing it. A formula for calculating the volume was derived. The veracity and reliability of the method have been proved by the testing results.The influence of geometrical shape of PDC on C-ratio testing was also studied. The obtained results show that the test values of PDC wear resistance increase with the increasing of geometric angles.Conventional mechanical properties of PCD, such as Young’s modulus and Poisson’s ratio,were tested using Instronl342 testing machine.The obtained results show that it’s feasible to measure the Young’s modulus and Poisson’s ratio of PCD by simple compressive loading test.Comparing to ultrasonic transfer velocity method and free vibration frequency method, the method used in present investigation is quite simple, reliable and cost-effective.Istron1342 testing machine and Hopkinson pressure bar(SHPB)were also used to obtain the strain rate varying from 10-6/s to 102/s,and the edgewise compressive strength of PDC in different loading speeds were successfully obtained.The relationship between loading speed and edgewise compressive strength of PDC is presented. The compressive strength under this loading condition for intact and damaged PDC were also obtained. The relationship among damage, loading speed and thickness of PCD layer is presented. This research provides the theoretical and experimental basis for reusing the damaged PDC.A new technique which combines non-planar junction with gradient transition is proposed, with which an inner gradient layer is designed in PDC.It can decrease the greatly problem on the residual stresses in flat-interface PDC.It’s excellent service performance was proved by the results of numerical analysis, experimental investigation and in-site drilling test. This new design has been successfully applied for a patent.Rock drilling feature and mechanism of PDC bit in service were studied.A numerical mode for calculating the PDC strength when cutting rock was then presented, which provides the theoretical basis for choosing the working parameters of PDC cutter. On this basis a new PDC cutter was designed and used in the Daqing oil well drilling. The obtained results show the excellent service performance of the new PDC.In short, the research work in this dissertation is based on the frontal of the subject, which is combined closely with engineering practice.The theoretical analysis and methods of mathematical,mechanical,numerical simulation and advanced experimental means,were used in studying on the residual stresses and interface optimization of PDC.It founded a theoretical and technical basis for studying thermal residual stress fracturing and preventing fracture.This research is helpful for reducing effectively the residual stresses, optimizing the composition of the interface and improving the eligible rate in manufacturing.It is of important theoretical significance and engineering application prospect.更多还原