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Ti-Nb alloys are high-profile candidates for the biomedical applications. However, because of poor surface integrity (i.e. residual stress and surface roughness), Ti-Nb implantable medical devices need to be machined in order to obtain functional surfaces finish. In this work, experimentaland numerical investigations are conducted to study the micro-cutting response of Ti42Nb titanium alloy produced by laser-based powder bed fusion. Experimental micro-cutting tests are carried out using precision turning lathe. Trials are performed with two cutting velocities of 60 m/min and 120 m/min and different feed rates, varying from 5 to 40μm/rev. For the numerical study, a porous crystal plasticity-based model is proposed to address the impact of anisotropy and microstructure heterogeneities of the polycrystalline material. The crystal plasticity-basedmodel is identified using strain–stress curves obtained from compression tests performed under two strain rates and a wide range of temperatures. Numerical micro-cutting simulations are performed in order to gain insight into the impact of microstructural features (i.e. crystallographic orientation and grain size) on the machinability of the alloy.According to the results, the effect of the strain rates and the temperature on the thermomechanical behavior of the Ti42Nb titanium alloy produced by laser-based powder bed fusion is correctly depicted. The model captured the strain localization on adiabatic shear band during compression tests. According to the micro-cutting simulations, the local variables such as temperature, damage and plastic deformation are strongly impacted by the crystallographic orientations and the grain size.In addition, depending on the crystallographic orientations, the chip morphology changes form continues, slightly segmented to largely segmented.

In order to simulate micromachining of Ti-Nb medical devices produced in situ by selective laser melting, it is necessary to use constitutive models that allow one to reproduce accurately the material behavior under extreme loading conditions. The identification of these models is often performed using experimental tension or compression data. In this work, compression tests are conducted to investigate the impact of the loading conditions and the laser-based powder bed fusion (LB-PBF) building directions on the mechanical behavior of β-Ti42Nb alloy. Compression tests are performed under two strain rates (1 s−1 and 10 s−1) and four temperatures (298 K, 673 K, 873 K and 1073 K). Two LB-PBF building directions are used for manufacturing the compression specimens. Therefore, different metallographic analyses (i.e., optical microscopy (OM), scanning electron microscopy (SEM), energy-dispersive X-ray (EDX), electron backscatter diffraction (EBSD) and X-ray diffraction) have been carried out on the deformed specimens to gain insight into the impact of the loading conditions on microstucture alterations. According to the results, whatever the loading conditions are, specimens manufactured with a building direction of 45∘ exhibit higher flow stress than those produced with a building direction of 90∘, highlighting the anisotropy of the as-LB-PBFed alloy. Additionally, the deformed alloy exhibits at room temperature a yielding strength of 1180 ± 40 MPa and a micro-hardness of 310 ± 7 HV0.1. Experimental observations demonstrated two strain localization modes: a highly deformed region corresponding to the localization of the plastic deformation in the central region of specimens and perpendicular to the compression direction and an adiabatic shear band oriented with an angle of ±45 with respect to same direction.

International audience; During every machining operation, a part of the energy necessary to cut dispels into heat. Heat is associated with the plastic deformation in the different shear zones (even for bone tissues; Liao and Axinte 2016), and with the frictional dissipation energy generated at the tool-chip interface and at the interface between tool and sample. During surgery, bone drilling leads therefore to an increase of temperature that can potentially cause osteonecrosis, if the level of temperature and/or the duration of exposition is too high. The recent work of Feldmann et al (2018) showed that the heat conductivity of bone tissues is highly dependent on the bone volume fraction. As this volume fraction is varying locally inside bone tissues, a systematic experimental campaign allowing to identify the heat sources during drilling is hard to conduct. To counter this difficulty, a homogeneous and porosity-controlled material is used in the present experimental work to identify the causes of the thermal loading into the sample. The results of the experiments will allow to improve the analytical model previously developed (Amewoui et al. 2019) for predicting the temperature during bone drilling.

International audience; Predicting the bone thermal response in a surgical operation remains a major challenge. In the previous works, metal machining theory has frequently been used to predict bone temperature in drilling process. However, several experimental studies demonstrate that the chip formation process is very complex compared to metal cutting. In the present study, a simplified analytical model based on the moving heat source approach combined with the method of image sources is developed. The heat source due to the drill-bit tip was supposed to be proportional to the cutting energy. The friction at the tool-hole contact was also considered. An experimental study was performed on fresh femur pig bone for cutting speeds from 2 to 20 m/min. Temperature rise, drilling forces and bone volume fraction were measured. The experimental validation showed that the model reproduces satisfactorily the increase in temperature up to the maximum value while it overestimates the temperature during the cooling stage. A parametric study (thermal boundary conditions, lateral friction) was also performed. From the predicted results, it appears that the model can be improved by considering the effects of the bone volume fraction which can present a significant variation in the bone sample.

International audience; BackgroundA new model of 3D-printed temporal bone with an innovative distinction between soft and hard tissues is described and presented in the present study. An original method is reported to quantify the model’s ability to reproduce the complex anatomy of this region.MethodsA CT-scan of temporal bone was segmented and prepared to obtain 3D files adapted to multi-material printing technique. A final product was obtained with two different resins differentiating hard from soft tissues. The reliability of the anatomy was evaluated by comparing the original CT-scan and the pre-processed files sent to the printer in a first step, and by quantifying the printing technique in a second step. Firstly, we evaluated the segmentation and mesh correction steps by segmenting each anatomical region in the CT-scan by two different other operators without mesh corrections, and by computing distances between the obtained geometries and the pre-processed ones. Secondly, we evaluated the printing technique by comparing the printed geometry imaged using µCT with the pre-processed one.ResultsThe evaluation of the segmentation and mesh correction steps revealed that the distance between both geometries was globally less that one millimeter for each anatomical region and close to zero for regions such as temporal bone, semicircular canals or facial nerve. The evaluation of the printing technique revealed mismatches of 0.045±0.424 mm for soft and −0.093±0.240 mm for hard tissues between the initial prepared geometry and the actual printed model.ConclusionsWhile other reported models for temporal bone are simpler and have only been validated subjectively, we objectively demonstrated in the present study that our novel artificial bi-material temporal bone is consistent with the anatomy and thus could be considered into ENT surgical education programs. The methodology used in this study is quantitative, inspired by engineer sciences, making it the first of its kind. The validity of the manufacturing process has also been verified and could, therefore, be extended to other specialties, emphasizing the importance of cross-disciplinary collaborations concerning new technologies.

The present experimental work investigates the response of woven glass fabric reinforced polyamide 6.6/6 subjected to drop weight impact loading. The main objective is the development and the introduction of a new experimental procedure/approach, based on different complementary detection techniques, that aims at investigating the damage induced by impact loading in thermoplastic woven fabric composites. The developed approach is intended to be generalized to other types of composite materials. The main idea is to assess all the experimental results obtained through the developed procedure with a direct investigation method. The latter consists in the Permanent Indentation (PI) measurement providing an indicator of the damage criticality in the composite sample. To this end, several non-destructive testing methods are carried-out and their experimental findings are analyzed and cross-linked. The identification of the different damage mechanisms, caused by the drop weight impact, is performed using X-Ray micro-computed tomography (mCT). C-scan ultrasonic investigation is conducted according to two types: transmission and reflection for the detection of the impact damage and the identification of the induced degradation area. B-scan imaging are then obtained through specific post-processing of the impacted surface to extract the permanent indentation (PI). The latter is validated through surface flatness measurement using the highly resolved 3D optical profilometry. The correlation between the X-Ray tomography results and the permanent indentation measurement is then established. It correlates the PI level with the damage mechanisms of a barely visible impact damage (BVID) in woven glass reinforced polyamide 6.6/6 composite. The author(s) disclosed receipt of the following financial support for the research, authorship, and/or publication of this article: The present work is co-funded by Groupe PSA and ANRT. It is made in the framework of the OpenLab Materials and Processes involving Groupe PSA, Arts et Metiers (ENSAM) and Georgia Tech Lorraine.

International audience; Bone drilling is a common operation in orthopaedic and dental practices. This operation generates heat resulting mainly from friction between bone hole wall, chips and drill bit body. Heat generation during bone drilling exposes bone cells to elevated temperature and may result in thermonecrosis. Although many experimental investigations have been conducted to characterize the optimal drilling conditions, conclusions are still uncertain and diverging (Pandeyand Panda 2013). In the present study, a semi- analytical model, based on the moving heat source approach combined with the method of image sources, is developed for predicting the temperature during bone drilling. An experimental drilling campaign on porcine bone samples is conducted in parallel, to validate the model.

International audience; Parts produced by Selective Laser Melting (SLM) presents a roughness due to thickness of fusion layers but also to partially sintered particles stuck to the edge of the parts. In order to ensure a finished product with the dimensional and structural requirements of an industrial part, a post processing by machining is necessary. The aim of the proposed study is to compare the machinability of Ti-6Al-4V obtained by SLM process and that of a cast alloy. Micro-cutting tests are conducted to examine the effect of operating conditions on cutting forces, chip formation and on surface and sub-surface microstructure. .

International audience; In the modelling approach of bar turning, the accurate prediction of the Chip Flow Direction represents a real challenge; it directly affects the axial and radial components of the cutting forces, and consequently the temperature distribution in the rake face. Chip flow direction is one aspect of chip control which is an important key factor in turning operations optimization. The aim of the present work is to propose an analytical approach of modelling to determine the chip flow direction in bar turning. Experimental tests and results complete the study and validate the proposed model.