Computational modeling of debonding behavior at the bone/cement interface with experimental validation

Both clinical examinations and in vitro physical experiments have shown that the fixation interfaces of cemented components are actually critical sites affecting the long-term stability and survival of prosthetic implants after implantation. This study aims to investigate the interfacial debonding behavior of bone/cement composite structures and attempts to establish an analysis model for clinical applications involving cemented prosthetic components. The mechanical properties of the bonded interface were characterized by interfacial strength, interfacial stiffness, and fracture toughness; the measured values of tensile strength, shear strength, and fracture toughness were 4.94 MPa, 5.94 MPa, and 0.34 MN/m^3/2, respectively. The measured strengths of the different configurations from this study are in good agreement with the experimental results available in the literature. In addition, we generated a finite element model with the same geometry as that of the experimental specimen used in the fracture test. The extent of interfacial debonding was further determined by means of the surface damage criteria and the fracture characteristics of the interface crack. The finite element model with an elastic interface predicted that the stress intensity factor (SIF) at the bone/cement interface crack varies nonlinearly with the applied load, which shows that the interface disintegrates at the load level, as was measured in the fracture experiments. It was possible to verify that the proposed simulation model was capable of describing the interfacial mechanical behavior of cemented components.     

Effect of residual stresses on mechanical properties and interface adhesion strength of SiN thin films

Residual stresses play a significant role in the mechanical reliability of thin films. Thus in this study, the mechanical properties and interface adhesion strengths of SiN thin films containing different residual stresses have been investigated by using nanoindentation and nanoscratch tests. With varied residual stresses from compressive to tensile, the penetration depth of nanoindentation tests shifted to a higher value. The hardness and elastic modulus decreased from 11.0 and 95 GPa, respectively, for the film containing a compressive stress of 235 MPa to 9.6 and 84 GPa for the film with a tensile stress of 86 MPa. With decreasing compressive stress and increasing tensile stress, the interface adhesion energy decreased from 1.8 to 1.5 J/m². Compressive stresses were expected to blunt crack tips and inhibit crack propagation, while tensile stresses enlarged crack opening and facilitated crack propagation, thus changing the mechanical properties of the SiN thin films.     

Time-dependent lateral pressure of the filling barricade for roadway cemented backfill mining technology

The filling barricade is one of the key components of roadway cemented backfill systems and this research focuses on critical factors influencing the performance of these systems, particularly the lateral stress characteristics and the stability of the filling barricade. In this paper, a theoretical model is presented and applied to obtain and calculate the lateral pressures exerted on the filling barricade and to understand the effects of the filling process. It is found that the yield stress of cemented backfill increases with curing time and this relationship can be described as an increasing power function. The lateral stresses exerted on the filling barricade increase over time during the filling period but decrease over time during the waiting period. Both the maximum lateral stress exerted on the filling barricade and the decreasing amplitude decrease as the number of filling rounds increases. In the calculation case, the maximum lateral stress declines from 0.161 MPa to 0.0148 MPa when the number of filling rounds increases from one to six. From these results, the filling process with three rounds is determined to be the optimal process scheme. In the first round, the lateral stress increases to 0.0369 MPa during the filling period and decreases to 0.0146 MPa during the waiting period; In the second round, the lateral stress increases to 0.0368 MPa then decreases to 0 MPa; in the third round, the lateral stress of the filling barricade stays at 0 MPa.

     

板状WC晶粒WC-(Co-Ni)硬质合金的组织和性能

采用真空烧结法制备了板状WC晶粒WC-(Co-Ni)硬质合金,通过XRD、SEM、EDS等手段研究了Ni/(Ni+Co)比对硬质合金组织和性能的影响规律。结果表明:随着Ni/(Ni+Co)比的增大,硬质合金显微组织中板状WC晶粒的比例逐渐减少,硬质相颗粒的尺寸逐渐增大且平均长厚比逐渐减小。当Ni/(Ni+Co)比过大时,硬质合金中硬质相颗粒出现了团聚现象,使其力学性能显著降低。当Ni/(Ni+Co)比为0.3和0.5时,WC-(Co-Ni)硬质合金的综合力学性能较高,这与其硬质相颗粒较细和平均长厚比较大有关。当Ni/(Ni+Co)比为0.5时,WC-(5Co+5Ni)硬质合金具有较优的综合力学性能,其抗弯强度、硬度和断裂韧性分别为2 448 MPa、90.0HRA、21.2 MPa·m~(1/2)。     

Modelling the mixed-mode failure of cement-bone interfaces

The main purpose of this study is the development of a failure model for the cement-bone interface in cemented hip prostheses. The model includes the mechanical behaviour of the cement-bone interface under mixed-mode loading, reproducing the initial linear behaviour up to a certain stress level, followed by an exponential strain-softening region. Four parameters for each stress mode (tension and shear) must be defined in order to fully characterize this mechanical behaviour: the interface strength t₀, the initial stiffness K₀, the interface displacement corresponding to full debonding of the interface δ_c and the failure energy G_c. To validate the potential of the associated numerical model, several tests were simulated, obtaining results close to the experimental ones. This formulation was also applied to simulate a more biomechanical although still academic problem: the debonding evolution of the bone-cement interface of the Exeter total hip arthroplasty system, including fatigue failure of the interface. We conclude that the mixed-mode failure interface model here proposed allows for more realistic simulations of the debonding process of cement-bone interfaces.     

Improved shape memory composites combined with TiNi wire and shape memory epoxy

In order to develop high functionality of shape memory materials, the shape memory composites combined with TiNi wire and shape memory epoxy were fabricated, and the mechanical and thermomechanical properties were studied. The results showed that TiNi wire can compensate for the stiffness decrease of SMPs at elevated temperature, and the strength of interface and strength of interface matrix were important to further increase elevated temperature mechanical properties. The recovery stress of composites could be adjusted by changing the pre-strain, and the maximum recovery stress was obtained at 8% which was TiNi wire maximum recoverable strain. The addition of 1 vol% TiNi wire could increase the maximum recovery stress from 1.36 MPa to 4.04 MPa, which was almost 3 times of the matrix and at the same time maintained the rates of shape fixity and shape recovery close to 100%.     

Mechanical and leakage behaviour of the dentin – adhesive interface

Dentine bonding systems (DBS) have been developed in order to bond restorative materials (i.e. composite) to the inner walls of the tissues when function and integrity as to be restored. Adhesion to dentine results from the penetration of DBS into the demineralised substrate constituted by a swollen collagen network. The short-term stability of a restored tooth is mainly affected by the presence of defects which act as stress raiser, while the long-term stability of a restored tooth is mainly affected by the seal of the restorative material on the dental structures. In order to determine the properties of the material interface, bonding to dentine is analysed using micro-tensile static and dynamic tests, assisted by the finite element modelling (FEM) and by the X-ray computed microtomography (micro-CT). The effect of voids and porosity in the composite layer of the DBS on the stress distribution has been investigated. Tensile adhesive strength for a particular DBS was measured on cylindrical specimens. The dual energy absorption technique, with the synchrotron beam light, has been developed to investigate, in a non-destructive manner, the leakage at the dentine-DBS interface of a silver nitrate staining solution as a function of mechanical cycling. The results indicate that leakage occurs radially through the dentine-adhesive interface and is influenced by the porosity in the adhesive and composite layers.     

Brazing of WC–8Co cemented carbide to steel using Cu–Ni–Al alloys as filler metal: Microstructures and joint mechanical behavior

Three novel Cu–Ni–Al brazing filler alloys with Cu/Ni weight ratio of 4:1 and 2.5–10 wt% Al were developed and characterized, and the wetting of three Cu–Ni–Al alloys on WC–8 Co cemented carbide were investigated at 1190–1210?C by the sessile drop technique. Vacuum brazing of the WC–8 Co cemented carbide to SAE1045 steel using the three Cu–Ni–Al alloys as filler metal was further carried out based on the wetting test results. The interfacial interactions and joint mechanical behaviors involving microhardness, shear strength and fracture were analyzed and discussed. The experimental results show that all the three wetting systems present excellent wettability with final contact angles of less than 5?and fast spreading. An obvious degeneration layer with continuous thin strip forms in the cemented carbide adjacent to the Cu–Ni–Al/WC–8 Co interface. The variation of microhardness in the joint cross-section is closely related to the interactions(such as diffusion and solid solution) of WC–8 Co/Cu–Ni–Al/steel system. Compared with the other two brazed joints, the WC–8 Co/Cu–19 Ni–5 Al/steel brazed joint presents more reliable interlayer microstructure and mechanical property while brazing at the corresponding wetting temperatures for 5 min, and its average shear strength is over 200 MPa after further optimizing the brazing temperature and holding time. The joint shear fracture path passes along the degeneration layer, Cu–Ni–Al/WC–8 Co interface and brazing interlayer, showing a mixed ductile-brittle fracture.     

Mechanical testing of titanium/aluminium–silicon interfaces by push-out

Mechanical properties of Ti/Al–7Si assemblies produced by insert moulding were studied with a classical push-out test and a variant that is the circular-bending test. Special care has been taken for controlling both the reactivity at the Ti/Al–7Si interface and the metallurgical health of the Al–7Si matrix. Mechanical tests until complete debonding have been completed with interrupted tests, metallographic characterizations and FEM analysis of elastic stress state. A mean shear strength of the interface of about 120 MPa was obtained. When the Ti insert is solely fretted in the matrix, without chemical interaction between Ti and the Al–7Si alloy, the mean shear strength is significantly lower (48 MPa). This result clearly shows that chemical interaction at the interface (formation of a thin TiSi layer at the Ti side and a thick Al₃Ti(Si) layer at the Al–7Si alloy side) improves the mechanical properties of the assembly. It is also shown that the failure sequence is characterized both by crack propagation from bottom to top and matrix yielding from top to bottom. Actually, interface damaging begins by crack initiation at the specimen bottom face (not at the top face and under the indenter) in a nearly pure mode I solicitation at a radial tensile stress of about 100 MPa.     

Dissimilar welding of WC–Co cemented carbide to Ni42Fe50.9C0.6Mn3.5Nb3 invar alloy by laser–tungsten inert gas hybrid welding

Dissimilar welding between cemented carbide and invar alloy was carried out using CO₂ laser beam and argon arc as heat sources. η Phase was formed near WC–Co/weld interface and precipitations in the fracture were discovered. In order to disclose the microstructure and mechanical property, firstly, η phase’s morphology and composition at interface were investigated using backscattered electron imaging (BEI); and element diffusion across heat affected zone near WC–Co/weld interface was further studied. Secondly, bend strength values of butt joint with different welding parameters were tested by four-point bend strength experiment. Finally, WC migration mechanism was further discussed and the bend strength was measured. The results showed: (1) microstructures consisted of columnar crystals, cellular crystals, eutectic structure and fir-tree crystal and dendritic crystals. The columnar crystals were surrounded by lots of fir-tree crystals. (2) WC migration was driven by stirring effects of welds, high pressure of molten materials and ionized shielding gas, interface reaction and surface tension. (3) η Phases dispersion did not decrease bend strength of butt joint. And the maximum bend strength was 1493.56 MPa, which was attributed to NbC precipitations featured with super-fine fir-tree.     

Biochemical and histological evaluation of human synovial-like membrane around failed total hip replacement prostheses during in vitro mechanical loading

The biochemical role of the synovial-like membrane formed at the interface of eight aseptic failed total hip prosthesis has been investigated during in vitro mechanical loading. The study was carried out on four membranes from cemented prosthesis and four titanium alloy uncemented ones. Intermittent positive pressure leading to 20% deformation of the membrane (100 g/cm²)was applied to the membrane fragments in cycles (300 cycles/15 min) repeated three times at thirty minutes intervals in which interleukin-6 (IL6), prostaglandin-E2 (PGE2) and interleukin-1 (IL1) levels were quantified both in culture media and in tissue extracts. Histological, morphometrical and immunohistochemical studies were also carried out on the same membranes.Mechanical stress evidenced an increase in the release of the examined cytokines both in cemented and uncemented prosthesis tissues; particularly evident was IL6 trend of increase from cemented prosthesis and IL1 result from uncemented ones. Histomorphological and immunohistochemical data revealed no differences between membranes obtained from cemented and uncemented prosthesis as to cell proliferation, fibrosis, macrophages lymphocytes B and T population, vessels and nervous fibers. The results indicate that mechanical stress plays a fundamental role in increasing membrane production and release of cytokines known as bone-resorbing agents. Furthermore, the histologic finding of synovial-like membrane with the same histomorphological and immunohistochemical findings but with different biochemical response to mechanical stimulation, suggests that cells involved in the production and release of the considered mediators might have different strain behavior by different development conditions (previous contact with PMMA). © 2001 Kluwer Academic Publishers     

Ti添加对WC-Ni3Al硬质合金微观组织与力学性能的影响

为提高WC-Ni₃Al硬质合金的力学性能，采用放电等离子烧结制备Ti掺杂的WC-Ni₃Al硬质合金，并研究不同Ti添加量对WC-Ni₃Al硬质合金微观组织和力学性能的影响。结果表明: Ti的添加减小WC-Ni₃Al块体样品中反应生成的少量Al₂O₃的尺寸，并且使Al₂O₃的分布更加均匀。一方面，小尺寸的Al₂O₃与原位生成的(Ti, W)C协同提高WC-Ni₃Al块体样品的硬度；另一方面，适量Ti的添加还提高WC-Ni₃Al硬质合金的断裂韧度，这是由于原位生成的(Ti, W)C与WC有较好的界面结合，增加对裂纹扩展的桥接与偏转作用。当添加3%(质量分数)的Ti时，WC-Ni₃Al硬质合金获得了优异的力学性能，硬度和断裂韧度分别为(19.29±0.18) GPa和(13.14±0.24) MPa·m^1/2。     

高强高模聚酰亚胺纤维/环氧树脂复合材料力学性能与破坏机制

以高强高模聚酰亚胺（PI）纤维为增强体,以航空级环氧树脂（EP）为基体,通过热熔法制备预浸料并采用热压罐成型技术制备了PI/EP复合材料层合板,对其力学性能和破坏形貌进行了分析。结果表明:高强高模PI纤维与EP具有良好的界面结合力,PI/EP复合材料的层间剪切强度为65.2 MPa,面内剪切强度为68.6 MPa;良好的界面结合状态能充分发挥PI纤维优异的力学性能,PI/EP复合材料的纵向拉伸强度达1 835 MPa,弯曲强度为834 MPa;PI/EP复合材料纵向拉伸破坏模式为散丝爆炸破坏,同时由于高强高模PI纤维还具有优异的韧性和较高的断裂伸长率,PI/EP复合材料从受力到失效断裂的时间较长;PI/EP复合材料纵向压缩破坏模式为45°折曲带破坏。高强高模PI/EP复合材料为航空航天先进复合材料增加了一个全新的选材方案。      

超细碳化钨-钴硬质合金的原子力显微镜研究

以液相复合-连续还原碳化方法制备的纳米碳化钨-钴复合粉末为原料,采用低压烧结制备了性能优良的超细碳化钨-钴硬质合金.运用原子力显微镜(AFM)对超细碳化钨-钴硬质合金的表面形貌进行了观察、缺陷和粒度分析,同时对合金的力学性能进行了测试.结果表明,采用低压烧结获得的烧结试样的洛氏硬度HRA≥93.5,抗弯强度TRS≥3300MPa,平均晶粒度＜220nm.制备了具有高强度、高硬度的超细碳化钨-钴硬质合金.纳米碳化钨-钴复合粉末制备的超细硬质合金组织结构均匀,但局部仍然存在着组织缺陷,分析了产生缺陷的机理.     

Performance of bioactive PMMA-based bone cement under load-bearing conditions: an in vivo evaluation and FE simulation

In the past, bioactive bone cement was investigated in order to improve the durability of cemented arthroplasties by strengthening the bone-cement interface. As direct bone–cement bonding may theoretically lead to higher stresses within the cement, the question arises, whether polymethylmethacrylate features suitable mechanical properties to withstand altered stress conditions? To answer this question, in vivo experiments and finite element simulations were conducted. Twelve rabbits were divided into two groups examining either bioactive polymethylmethacrylate-based cement with unchanged mechanical properties or commercially available polymethylmethacrylate cement. The cements were tested under load-bearing conditions over a period of 7?months, using a spacer prosthesis cemented into the femur. For the finite element analyses, boundary conditions of the rabbit femur were simulated and analyses were performed with respect to different loading scenarios. Calculations of equivalent stress distributions within the cements were applied, with a completely bonded cement surface for the bioactive cement and with a continuously interfering fibrous tissue layer for the reference cement. The bioactive cement revealed good in vivo bioactivity. In the bioactive cement group two failures (33?%), with complete break-out of the prosthesis occurred, while none in the reference group. Finite element analyses of simulated bioactive cement fixation showed an increase in maximal equivalent stress by 49.2 to 109.4?% compared to the simulation of reference cement. The two failures as well as an increase in calculated equivalent stress highlight the importance of fatigue properties of polymethylmethacrylate in general and especially when developing bioactive cements designated for load-bearing conditions.     

Mechanical testing of plasma-sprayed ceramic coatings on metal substrates: Interfacial fracture toughness and tensile bond strength

Plasma-sprayed ceramic coatings applied to metal components have uses in many diverse fields, including aerospace, electronics and, more recently, biomaterials. In all such applications success of the component relies on adequate bonding between the ceramic coating and metal substrate. In this study, a convenient and reliable test method to assess the fracture toughness of this metal/ceramic interface was developed by modifying an existing homogeneous short-bar configuration. Additionally, conventional tensile adhesive bond strength testing was conducted. For the alumina-coated Ti-6Al-4V model system studied, an interface toughness value of 1.84±0.20 MPa m^1/2 was obtained. An interfacial tensile bond strength of 13.6±2.9 MPa was also measured for this system. Further refinement of this modified short bar technique taking into account experimental compliance behaviour and potential complex or mixed-mode stress intensities is needed to confirm these preliminary toughness values, which nevertheless offer a potentially more sensitive means of monitoring the mechanical integrity of this metal/ceramic interface.     

CVD-SiC界面改性涂层对气相渗硅制备C_f/SiC复合材料力学性能的影响

在气相渗硅制备C_f/SiC复合材料时,界面改性涂层非常重要。良好的界面改性涂层一方面起到保护碳纤维不受Si反应侵蚀的作用,另一方面起到调节纤维和基体界面结合状况。通过在C纤维表面制备CVD-SiC涂层来进行界面改性,研究CVD-SiC界面改性涂层对GSI C_f/SiC复合材料力学性能和断裂特征的影响,并分析其影响机制。结果表明:无CVD-SiC涂层改性的C_f/SiC复合材料力学性能较差,呈现脆性断裂特征,其强度、模量和断裂韧度分别为87.6MPa,56.9GPa,2.1MPa·m1/2。随着CVD-SiC涂层厚度的增加,C_f/SiC复合材料的弯曲强度、模量和断裂韧度呈现先升高后降低的趋势,CVD-SiC涂层厚度为1.1μm的C_f/SiC复合材料的力学性能最好,其弯曲强度、模量和断裂韧度分别为231.7MPa,87.3GPa,7.3MPa·m1/2。厚度适中的CVD-SiC界面改性涂层的作用机理主要体现在载荷传递、"阻挡"Si的侵蚀、"调节"界面结合状态3个方面。     

Cu部分代Co超细硬质合金研究

基于Cu与Co相同的晶型结构和相似的原子结构,采用共沉淀方法,制备Cu部分代Co的WC—10Co硬质合金,研究Cu对材料的组织和力学性能的影响。实验结果表明,通过Cu—Co共沉淀方式将cu加入粘接相中,形成Co（Cu）固溶体,在液相烧结过程中Cu均匀地分布在Co中,可以降低WC在粘接相中的溶解度,有效阻碍WC颗粒的溶解...     

Joining molybdenum to aluminium by diffusion bonding

The joining of molybdenum to aluminium and aluminium-copper alloy using diffusion bonding has been investigated. Bond strengths have been measured by means of a simple shear jig and the joint microstructures characterized by electron microscopy and electron-probe microanalysis. Successful joints were produced by using a copper foil interlayer to form a eutectic liquid during the bonding process which helped disrupt the oxide film on aluminium and promote metal diffusion across the joint interface. When bonding commercial-purity aluminium to molybdenum, the iron present as an impurity caused a ternary eutectic liquid to form and, after solidification of the liquid phase, a thin film of Al₇Cu₂Fe was left behind on the aluminium. Failure of this joint occurred at a shear stress of 75 MPa, with the fracture path contained within the aluminium. With super-purity aluminium, a binary eutectic liquid was produced and the ensuing interface reaction resulted in a multi-layered structure of molybdenum-containing phases. The bond failed at the molybdenum interface at a stress of 40 MPa. When bonding aluminium-copper alloy to molybdenum without a copper interlayer, general melting at the interface via eutectic phase formation did not occur and the interface showed only localized reaction. The joint failed by separation from the molybdenum, at a stress of 25 MPa. When, however, a copper interlayer was used, fairly thick regions of multi-layered molybdenum intermetallics formed and the remaining surface was covered by a layer of Al₇Cu₂Mo phase. Failure of this joint occurred at a stress of 70 MPa, mainly by separation at the molybdenum interface.     

Measurement of interface strength in Al/SiC particulate composites

Fracture in particulate-reinforced metal-matrix composites is initiated by particulate cracking and interface decohesion, and crack propagation occurs through the matrix, particulate and interface. A ‘critical stress partition’ model is described which considers the proportions of matrix, particulate and interface for which the fracture stress is exceeded. Tensile tests and microhardness measurements are reported for SiC/Al metal-matrix composites having particulate volume fractions of 0–20%. Measurements of the fractions of cracked and interface-debonded particulate before and after final fracture are combined with the fracture model to calculate the interface strength, σ_int′. The values of σ_int′ obtained are 469 MPa for uncoated SiC particulate and 438 MPa for particulate coated with a thin layer of Al₂O₃ to prevent interface reaction. The tensile results indicate that the weaker interfaces promote interface debonding and increase percent elongation.