The study of bone mineral density in postmenopausal women with rheumatoid arthritis

زمینه و هدف: کاهش تراکم مواد معدنی موجب بروز پوکی استخوان و عوارض ناشی از آن می شود. مطالعه حاضر با هدف بررسی وضعیت تراکم معدنی استخوان بر اساس رده های مختلف سنی در زنان یائسه مبتلا به آرتریت روماتوئید انجام شده است. روش بررسی: مطالعه توصیفی-تحلیلی حاضر، بر روی 98 زن یائسه مبتلا به آرتریت روماتوئید مراجعه کرده به بیمارستان آموزشی درمانی 5 آذر شهرستان گرگان که نتایج سنجش تراکم استخوانی آنان در پرونده موجود بود، انجام شد. اطلاعات لازم به وسیله پرسشنامه از پرونده های بیماران استخراج گردید. داده ها با استفاده از آزمون های آماری آماره های توصیفی (فراوانی نسبی و فراوانی مطلق، میانگین و انحراف معیار) و آزمون های تحلیلی (رگرسیون، کای دو، ضریب همبستگی اسپیرمن و ANOVA)، مورد بررسی قرار گرفت. یافته ها: در مجموع 98 زن یائسه مبتلا به آرتریت روماتوئید با میانگین سنی39/9 ± 88/57 سال مورد بررسی قرار گرفتند. شیوع کلی استئوپروز 3/13 گزارش شد که با افزایش سن به طور معنی‌داری افزایش یافت (001/0

Additive manufacturing of high-strength continuous fiber reinforced polymer composites

Doctor of PhilosophyDepartment of Industrial & Manufacturing Systems EngineeringDong LinAdditive manufacturing (AM), also referred to as 3D printing, of polymer-fiber composites has transformed AM into a robust manufacturing paradigm and enabled producing highly customized parts with significantly improved mechanical properties compared to un-reinforced polymers. 3D printing of continuous carbon fiber reinforced thermoplastics (CFRTP) composites is increasingly under development owing to its unparalleled flexibility of manufacturing 3D structures over traditional manufacturing processes. However, key issues, such as weak interlayer bonding, voids between beads and layers, and low volume ratio of carbon fiber, in the mainstream fused deposition modeling (FDM) and extrusion suppress the applications of these techniques in mission-critical applications, such as aerospace and defense industries. In this work, we proposed a new laser assisted AM method that utilizes prepreg composites with continuous fiber reinforcement as feedstock to fabricate 3D objects by implementing laser assisted bonding and laser cutting. This technique is inspired by laminated object manufacturing (LOM), for AM of continuous CFRTPs using prepreg composite sheets. AM of continuous glass and carbon fiber reinforced thermoplastic composites is demonstrated using this technique. The continuous fiber reinforced prepreg is laser cut and laser bonded layer upon layer to produce 3D composite objects. Microstructure and mechanical properties (strength, modulus, interfacial, and shear properties) of the additively manufactured continuous fiber composites are studied and compared to other additive and conventional manufacturing methods. The interlayer properties of these additively manufactured composites was superior to other AM technologies, resulting to an excellent mechanical properties relative to other AM techniques. The microstructure analysis, by micro computed tomography (CT) scans, scanning electron microscopy (SEM), and optical microscopy, showed low void content and full consolidation of prepreg layers. The temperature at the material interface during the 3D process is crucial to achieve a strong bonding strength. This temperature can be predicted via the developed finite element (FE) heat transfer model in this work. This numerical model is able to predict the temperature history during the laser bonding process with great accuracy when compared to the experimental values. The surface quality of the additively manufactured CFRTPs were also studied and compared with the FDM technology. In addition, mechanical finishing methods, namely CNC milling and rotary ultrasonic machining (RUM), were employed to improve the surface quality of the 3D printed composites and drill precise holes in the structures. Overall, the proposed AM method can be broadly beneficial for industries requiring high performance and lightweight structural materials with complex geometries. This method is also easily scalable for high volume productions and could additionally reduce the waste associated with current CFRTP production techniques and improve the process from the production time standpoint by automation

Continuous trench, pulsed laser ablation for micro-machining applications

The generation of controlled 3D micro-features by pulsed laser ablation in various materials requires an understanding of the material's temporal and energetic response to the laser beam. The key enabler of pulsed laser ablation for micro-machining is the prediction of the removal rate of the target material, thus allowing real-life machining to be simulated mathematically. Usually, the modelling of micro-machining by pulsed laser ablation is done using a pulse-by-pulse evaluation of the surface modification, which could lead to inaccuracies when pulses overlap. To address these issues, a novel continuous evaluation of the surface modification that use trenches as a basic feature is presented in this paper. The work investigates the accuracy of this innovative continuous modelling framework for micro-machining tasks on several materials. The model is calibrated using a very limited number of trenches produced for a range of powers and feed speeds; it is then able to predict the change in topography with a size comparable to the laser beam spot that arises from essentially arbitrary toolpaths. The validity of the model has been proven by being able to predict the surface obtained from single trenches with constant feed speed, single trenches with variable feed speed and overlapped trenches with constant feed speed for three different materials (graphite, polycrystalline diamond and a metal-matrix diamond CMX850) with low error. For the three materials tested, it is found that the average error in the model prediction for a single trench at constant feed speed is lower than 5 % and for overlapped trenches the error is always lower than 10 %. This innovative modelling framework opens avenues to: (i) generate in a repeatable and predictable manner any desired workpiece microtopography; (ii) understand the pulsed laser ablation machining process, in respect of the geometry of the trench produced, therefore improving the geometry of the resulting parts; (iii) enable numerical optimisation for the beam path, thus supporting the development of accurate and flexible computer assisted machining software for pulsed laser ablation micro-machining applications

Effect of density and unit cell size grading on the stiffness and energy absorption of short fibre-reinforced functionally graded lattice structures

Architectured structures, particularly functionally graded lattices, are receiving much attention in both industry and academia as they facilitate the customization of the structural response and harness the potential for multi-functional applications. This work experimentally investigates how the severity of density and unit cell size grading as well as the building direction affects the stiffness, energy absorption and structural response of additively manufactured (AM) short fibre-reinforced lattices with same relative density. Specimens composed of tessellated body-centred cubic (BCC), Schwarz-P (SP) and Gyroid (GY) unit cells were tested under compression. Compared to the uniform lattices of equal density, it was found, that modest density grading has a positive and no effect on the total compressive stiffness of SP and BCC lattices, respectively. More severe grading gradually reduces the total stiffness, with the modulus of the SP lattices never dropping below that of the uniform counterparts. Unit cell size grading had no significant influence on the stiffness and revealed an elastomer-like performance as opposed to the density graded lattices of the same relative density, suggesting a foam-like behaviour. Density grading of bending-dominated unit cell lattices showcased better energy absorption capability for small displacements, whereas grading of the stretching-dominated counterparts is advantageous for large displacements when compared to the ungraded lattice. The severity of unit cell size graded lattices does not affect the energy absorption capability. Finally, a power-law approach was used to semi-empirically derive a formula that predicts the cumulative energy absorption as a function of the density gradient and relative density. Overall, these findings will provide engineers with valuable knowledge that will ease the design choices for lightweight multi-functional AM-parts

Advances in modeling transport phenomena in material-extrusion additivemanufacturing: Coupling momentum, heat, and mass transfer

Material-extrusion (MatEx) additive manufacturing involves layer-by-layer assembly ofextruded material onto a printer bed and has found applications in rapid prototyping.Both material and machining limitations lead to poor mechanical properties of printedparts. Such problems may be addressed via an improved understanding of thecomplex transport processes and multiphysics associated with the MatEx process.Thereby, this review paper describes the current (last 5 years) state of the art modelingapproaches based on momentum, heat and mass transfer that are employed in aneffort to achieve this understanding. We describe how specific details regardingpolymer chain orientation, viscoelastic behavior and crystallization are often neglectedand demonstrate that there is a key need to couple the transport phenomena. Such acombined modeling approach can expand MatEx applicability to broader applicationspace, thus we present prospective avenues to provide more comprehensive modelingand therefore new insights into enhancing MatEx performanc

Laser Surface Engineering of Hierarchy Hydroxyapatite Aerogel for Bone Tissue Engineering

Bioceramics with porous microstructure has attracted intense attention in tissue engineering due to tissue growth facilitation in the human body. In the present work, a novel manufacturing process for producing hydroxyapatite (HA) aerogels with a high density shell inspired by human bone microstructure is proposed for bone tissue engineering applications. This method combines laser processing and traditional freeze casting in which HA aerogel is prepared by freeze casting and aqueous suspension prior to laser processing of the aerogel surface with a focused CO2 laser beam that forms a dense layer on top of the porous microstructure. Using the proposed method, HA aerogel with dense shell was successfully prepared with a microstructure similar to human bone. The effect of laser process parameters on surface and cross-sectional morphology and microstructure was investigated in order to obtain optimum parameters and have a better understanding of the process. Low laser energy resulted in fragile surface with defects and cracks due to low temperature and inability of laser to fully melt the surface while high laser energy caused thermal damage both to surface and microstructure. The range of 40–45 W laser power, 5 mm/s scanning speed, spot size of 1 mmm and 50 % overlap in laser scanning the surface yielded the best surface morphology and micro structure in our experiments.</jats:p