Thermal residual stress of polycrystalline diamond compacts

Thermal residual stresses in polycrystalline diamond compact(PDC)cutter arising from the difference in thermal expansion between the polycrystalline diamond(PCD)and the supporting tungsten carbide substrate after sintering at high pressure and high temperature were investigated using finite element simulation,laboratory tests and theoretical analysis.The obtained results show that although compressive residual stresses exist both in the interface of PCD table and in the most region of PCD table surface, the tensile residual stress,which is a fatal shortage to PDC,can also occur near the outer diameter area of PCD table,and the maximum value is 690 MPa.Distribution of tensile stress in the PCD table is given through experimental results,which is well consistent with the numerical results.This finding may be significant in designing new PDC cutters with lower residual stress and high cutting behavior.

New Vitrified Bond Diamond Grinding Wheel for Grinding the Cylinder of Polycrystalline Diamond Compacts

In this work, a kind of new vitrified bond based on Li2O-Al2O3-SiO2 glass ceramics was used to bond the diamond grains, which is made into grinding wheel and the cylindrical grinding process of polycrystalline diamond compacts （PDCs） by using the new vitrified bond diamond grinding wheel was discussed. Several factors which influence the properties of grinding wheel such as amount of vitrified bond and the kinds and amount of stuff in grinding wheel were also investigated. It was found that the new vitrified bond can firmly combine diamond grains, when there are only diamonds and vitrified bond in the structure of grinding wheel, the longevity of the grinding wheel is about 2.5-3 times as that of resin bond grinding wheel for processing PDCs. The grinding size precision of PDCs can be improved from 4-0.03 mm to 4-0.01 mm because of larger Young＇s modulus of vitrified bond than resin bond. The grinding time of a PDC product can be 1.75-2.0 min from 3.25-3.5 min, so this kind of grinding wheel can save much time for processing PDCs. Also, there is hardly noise when using this new vitrified bond diamond grinding wheel to process PDCs. The amount of vitrified bond in grinding wheel influences the longevity of grinding wheel. When the size of diamond grains is 90-107 μm, the optimal amount of vitrified bond in grinding wheel is 21% （wt pct）. When the amount of vitrified bond exceeds 21%, there are many pores in grinding block, which will decrease the longevity of grinding wheel. The existence of addition stuff such as Al2O3 or SiC can reduce the longevity of grinding wheel.

Failure analysis of polycrystalline diamond compact cutters for breaking rock by bending waves theory

The breakage mechanism of the polycrystalline diamond compact(PDC) cutters was analyzed by the energy theory of bending waves. The cutting tests of granite block were conducted on a multifunctional testing device by using the cutter at three kinds of negative fore angles of 30°, 45° and 60°. The results show that, when the edge of the PDC layer is broken, the layer of tungsten cobalt is broken a little under the angle of 30°, while the layer of tungsten cobalt is broken continuously under the angle of 60°, their maximum depths are about 2 and 7 mm respectively in the two cases. The eccentric distance mainly depends on the negative fore angle of the cutter. When the cutter thrusts into the rock under an attack angle of 60°, the energy of bending waves reaches the maximum since the eccentric distance is the maximum. So the damage of cutter is the most serious. This test result is consistent with the conclusion of theoretical analysis well. The eccentric distance from the axial line of cutter to the point of action between the rock and cutter has great effect on the breakage of the cutter. Thus during the process of cutting, the eccentric distance should be reduced to improve the service life of PDC cutters.

激光-PDC钻头联合破岩机理及特性研究

随着我国油气勘探逐步向深层、超深层和复杂难钻岩层转移,现有的机械钻头存在着破岩效率低及作业成本高等问题。因此,提出了一种新型激光-PDC钻头,以实现高效破岩和节能降耗。采用有限元方法,基于岩石HJC(Holmquist-Johnson-Cook)本构模型,建立了激光-PDC(polycrystalline diamond compact,聚晶金刚石复合片)钻头联合破岩非线性动力学模型,开展了激光-PDC钻头联合破岩仿真研究。仿真结果表明:激光的辐射作用使岩石表面受辐射区域产生了较高的温度和较大的预应力,进而在岩石表面形成了相互贯穿的损伤带,降低了岩石强度,更有利于切削齿破碎岩石;与无激光单PDC钻头相比,激光-PDC钻头在破岩过程中受到的反扭矩降低了24.8%,钻头轴向加速度波动幅度降低了10.5%,钻进位移增加了8.67 mm,钻进速度提升了112.79%。搭建了激光-机械联合破岩实验台架,进行了激光-PDC钻头联合破岩实验。实验结果表明,激光-PDC钻头联合破岩有着更好的钻进稳定性和连续性,大大提高了破岩效率。研究结果为激光-机械破岩技术的发展和应用提供了一定的理论支撑和技术支持。

Optimization design and residual thermal stress analysis of PDC functionally graded materials

The distribution of thermal stresses in functionally graded polycrystalline diamond compact (PDC) and in single coating of PDC are analyzed respectively by thermo-mechanical finite element analysis (FEA). It is shown that they each have a remarkable stress concentration at the edge of the interfaces. The diamond coatings usually suffer premature failure because of spallation, distortion or defects such as cracks near the interface due to these excessive residual stresses. Results showed that the axial tensile stress in FGM coating is reduced from 840 MPa to 229 MPa compared with single coating, and that the shear stress is reduced from 671 MPa to 471 MPa. Therefore, the single coating is more prone to spallation and cracking than the FGM coating. The effects of the volume compositional distribution factor (n) and the number of the graded layers (L) on the thermal stresses in FGM coating are also discussed respectively. Modelling results showed that the optimum value of the compositional distribution factor is 1.2, and that the best number of the graded layers is 6.

Effect of tungsten carbide particles on microstructure and mechanical properties of Cu alloy composite bit matrix

Copper alloy composite bit matrix was prepared by pressureless vacuum infiltration,using at least one of the three kinds of tungsten carbide particles,for example,irregular cast tungsten carbide,monocrystalline tungsten carbide and sintered reduced tungsten carbide particles.The effects of powder particle morphology,particle size and mass fraction of tungsten carbide on the microstructure and mechanical properties of copper alloy composite were investigated by means of scanning electron microscopy,X-ray diffraction and abrasive wear test in detail.The results show that tungsten carbide morphology and particle size have obvious effects on the mechanical properties of copper alloy composites.Cast tungsten carbide partially dissolved in the copper alloy binding phase,and layers of Cu_(0.3)W_(0.5)Ni_(0.1)Mn_(0.1)C phase with a thickness of around 8–15μm were formed on the edge of the cast tungsten carbide.When 45%irregular crushed fine cast tungsten carbide and 15%monocrystalline cast tungsten carbide were used as the skeleton,satisfactory comprehensive performance of the reinforced copper alloy composite bit matrix was obtained,with the bending strength,impact toughness and hardness reaching 1048 MPa,4.95 J/cm^(2) and 43.6 HRC,respectively.The main wear mechanism was that the tungsten carbide particles firstly protruded from the friction surface after the copper alloy matrix was worn,and then peeled off from the matrix when further wear occurred.

Three-dimensional Numerical Prediction of the Flow and Temperature Field at the Surface of a PDC Bit

This paper provides a mathematical model and numerical method for predicting the velocity and temperature fields in the mud flows at the surface of a PDC (Polycrystalline Diamond Compact) bit. A 81/2' ( 21 59cm ) crown type PDC R bit is used as an example. The complex configuration of the PDC bit surface is resolved numerically using body fitting coordinates and the cutters are simplified as drag elements in the momentum equations and as heat source in the energy equation. The finite volume method is used to discretize the momentum and energy equations for the non Newtonian flow. The numerical results effectively predict the flow structure and temperature field which can be used to design and optimize the PDC bit.

Using Raman shift and FT-IR spectra as quality indices of oil bit PDC cutters

Nowadays many of oil and gas wells are drilled extensively by Polycrystalline Diamond Compact(PDC)drill bits.Various companies are manufacturing PDC cutters according to their usage.All of these companies concentrate their products of PDC cutters to be well resisting for abrasive wear.The wear of PDC inserts leads to money loss as well as delays the drilling procedures causing unexpected dilemmas.Therefore,it is crucially significant to evaluate the quality of the PDC cutters based on their resistance against abrasive wear.The present work concentrates on assessing the PDC cutters from various sources using two non-destructive analytical approaches:Raman-Shift and Fourier Transformation Infrared Ray(FT-IR)spectra.The analysis of the PDC samples with the analytical techniques were validated with the previous experimental results obtained from micro and nano-scratch tests achieved on the same specimens.The presented work could be performed on many PDC cutters from various manufacturers as the applied tests considered non-destructive compared to the traditional destructive techniques which leads the way for evaluating lots of PDC cutters without causing any damage.The analysis of the applied analytical approaches agreed with the results obtained from previous experimental scratch tests.