Effect of Titania Addition on Mechanical Properties and Wear Behavior of Alumina-10 wt.% Tricalcium Phosphate Ceramics as Coating for Orthopedic Implant

The aim of this study is to determine the effect of Titania on mechanical properties and wear behavior of Alumina-10 wt.% TCP ceramics and to evaluate the performance of Titania in improving their resistance to these effects. Al2O3–10 wt.% β-TCP mingled with TiO2 to obtain a mixture which is considered as a bioactive coating that may be used in orthopedic implants. Representative bioceramic samples of such blends were prepared with different percentages of Titania and then tested using different methods and techniques. Mechanical properties, fracture toughness were evaluated using the modified Brazilian, semi-circular bending specimens. A pin-on-disk tribometer was retained to study the wear behavior. Based on the obtained results, it was found that the best mechanical properties and wear resistance was displayed for Alumina-10 wt.% TCP-5 wt.% Titania composite. This composite presents a good combination of flexural strength (σf ≈ 98 MPa), compressive strength (σc ≈ 352 MPa), fracture toughness (KIC ≈ 13 MPa m1/2) and micro-hardness (Hv ≈ 8.4 GPa). In terms of tribological properties, the lowest wear volume and wear resistance was recorded for Al2O3–10 wt.% TCP − 5 wt.% TiO2 composition

Study of localized thinning of copper tube hydroforming in square section die : effect of friction conditions

International audienceThe friction conditions are responsible of the thickness distribution in a part realized by tube hydroforming. Then it is essential to have a good evaluation of the friction coefficient for running predictive finite element simulations. The tube expansion in a square die is one of tests proposed for the friction evaluation. In the literature, several analytical models have been developed for this specific test. The present paper concentrates on one of this model and results obtained from the analytical analysis, FE simulations and experiments are compared. The repartition of the thickness over the shaped tube and its evolution during the process are studied. The tendencies are in agreement but some complementary evaluations are proposed for using the proposed approach for the evaluation of the friction coefficient with the analytical model

Mechanical behavior and fracture characteristics of polymeric pipes under curved three point bending tests: Experimental and numerical approaches

International audienceThe present work deals with hierarchical composites in three dimensions, whose constituents behave as non-aging linear viscoelastic materials. We model the influence that imperfect viscoelastic interfaces have on the macroscopic effective response of these structures. As an initial approach, the problem of two bodies in adhesion is studied and in particular the case of soft viscoelastic interface at zero-order is considered. We deduce the integral form of the viscoelastic interface by applying the matched asymptotic expansion method, the correspondence principle, and the Laplace–Carson transform. Then, by adapting the integral form previously obtained, we address a heterogeneous problem for periodic structures. Here, theoretical results obtained for perfect interfaces are extended to the formal viscoelastic counterpart of the spring-type imperfect interface model. Finally, we show the potential of the proposed approach by performing calculations of effective properties in heterogeneous structures with two- and three-scale geometrical configurations and imperfect viscoelastic interfaces

Effect of the lubrication between the tube and the die on the corner filling when hydroforming of different cross-sectional shapes

International audienceThis paper presents an experimental study on corner filling in the tube hydroforming process. A single-step tube hydroforming process was retained based on pure expansion hydroforming with the conjunction of only internal pressure loading. Several hydroforming experiments were performed with differently shaped dies, such as a square, a rectangular, a trapezoidal, and a trapezoid-sectional die. The distribution of thickness was studied under both dry and lubricated conditions. The main results revealed that thinning occurred in the transition zone, between the corner radius and the straight wall, for both the square and rectangular dies. However, for the trapezoidal and trapezoid-sectional dies, the thinning took place in the sharp zone. The use of Teflon as a lubricant between the die and the tube led to significant changes in terms of thickness distribution and the reduction of thinning. For each of the various dies that were used, it was found that the lubrication of the contact tube/die offered a more uniform thickness for the final hydroformed product

Evaluation of the friction coefficient in tube hydroforming with the “corner filling test” in a square section die

International audienceFriction conditions are very critical in metal forming because they can lead to important thinning in the final manufactured product. The value of the friction coefficient is then of particular importance for performing predictive finite element (FE) simulation of forming operations. Classically, numerical simulations are run with values of the friction coefficient found in technical database where the Coulomb’s coefficient has been evaluated with the pin-on-disk test. Moreover, the friction coefficient is often used as a set up parameter for running FE simulations. The pin-on-disk test is not automatically suitable for characterizing the friction coefficient in tube hydroforming. The “corner filling” test has been developed for tube hydroforming and several authors have developed analytical models for representing this test. Among them, the authors have chosen to exploit the Orban-Hu model. This model permits to build graphs. On those graphs, experimental data are overlaid in order to evaluate the friction coefficient. Thus, a friction coefficient (μ) of 0.4 has been found by the proposed method against the value of about 0.1 found in technical database. FE simulations with 3D shell and 3D solid models have been performed with the two values of the friction coefficients. The conclusion is that FE simulations with 3D shell model permit definitely better predictions for thickness evaluation. Moreover, running the simulations with μ = 0.4 leads to a more critical representation of the minimal thickness in the final component. Finally, an experimental method is proposed for the evaluation of the friction coefficient without advanced numerical methods

On the friction effect on the characteristics of hydroformed tube in a square section die : analytical, numerical and experimental approaches

International audienceA focus on the effect of friction condition on tube hydroforming during corner filling in a square section die is proposed. Three approaches have been developed: an analytical model from the literature has been programmed, finite element simulations have been conducted and experiments have been carried out. Effect of friction coefficient on the thickness distribution in the square section of the hydroformed tube is studied. Critical thinning is found to take place in the transition zone between the straight wall and the corner radius and this minimal thickness seems to be the more appropriate parameter for the evaluation of the friction coefficient

Characterization of structural bonding under monotonic and cyclic loading

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Characterization of polylactic acid green composites and its biodegradation in a bacterial environment

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Combination of Numerical, Experimental and Digital Image Correlation for Mechanical Characterization of Al₂O₃/β-TCP Based on CDM Criterion

Cracks in engineering materials and structures can undergo different modes of deformation. This chapter presents a numerical and experimental approaches aimed to assess the fracture toughness and the Fracture behavior under tensile and shear loading of bioceramics based on commercial Alumina (Al2O3), synthesized Tricalcium phosphate (β-TCP). Conditioning was conducted at different percentages of TCP. After a sintering process at 1600°C for 1 hour, The Crack Straight Through Brazilian Disc were performed by image correlation during a mechanical test and numerical tests were carried out in order to find the angle where the pure mode II. A CDM based constitutive model was selected and implemented into a finite element code to study the damage of our bioceramics. The result of this combination was compared with the direction of crack propagation obtained experimentally. The directions of crack propagation found numerically were found in good agreement with those experimentally obtained by a mechanical test. Alumina-10 wt.% Tricalcium phosphate composites displayed the highest values of the fracture toughness. This value reached 8.76 MPa m1/2 MPa. The same optimal composition for the mode I and mode II stress intensity factor with maximum values of 7.6 MPa m1/2 and 8.45 MPa m1/2 respectively

On the tube hydroforming process using rectangular, trapezoidal, and trapezoid-sectional dies : modeling and experiments

International audienceIt is generally known that the contact between tube and die, in the case of tube hydroforming process, leads to the appearance of friction effects. In this context, there are many different models for representing friction and many different tests to evaluate it. In the present paper, the pin-on-disk test has been used and the theoretical model of Orban-2007 has been chosen and developed to evaluate friction coefficient. The main goal is to prove the capacity of theoretical model to present the friction conditions in comparison with the pin-on-disk test. From the Orban model, values of 0.05 and 0.25 of friction coefficient have been found under lubricated and dry tests, respectively. On the other hand, by the classical pin-on-disk test, other values were experimentally obtained as friction coefficient at the copper/steel interface. In the case of pure expansion hydroforming, based on an internal pressure loading only, a “corner filling” test has been run for tube hydroforming. Both dry and lubricated contacts have been considered. Various configurations and shapes have been studied such as the rectangular, trapezoidal, and trapezoid-sectional dies. Finite element simulations with 3D shell and 3D solid models have been performed with different values of friction coefficients. From the main results, it was found that the critical thinning occurs in the transition zone for the square and rectangular section die and in the sharp angle for the trapezoidal and trapezoid-sectional die. The comparison between numerical data and experimental results shows a good agreement. Moreover, the thickness distribution along the cross section is relatively consistent with those measured for the 3D shell model; however, the 3D solid models do not provide a realistic representation of the thickness distribution in the shaped tube. Finally, the results obtained from the theoretical model were more efficient than the results obtained from the pin-on-disk test