A numerical study on the cold sprayability of carbon fibre reinforced composites

One of the open questions in cold spraying on fibre reinforced composites is the optimal thickness of the top layer to provide a suitable base for successful deposition of the metallic particles and at the same time to hinder the probable damage of the fibres. In this study, a detailed finite element model is developed to study the deformation of a single Cu particle deposition on to polyether ether ketone (PEEK) substrate reinforced with carbon fibres. A PEEK layer with 30, 40 or 60 μm thickness was considered on the top surface of the composite. The particle impact velocity was varied in the range of 300-600 m/s to analyse its effects on the induced deformations as well as the structural integrity of the critical carbon fibres. It is believed that the proposed model can provide a helpful tool for predicting the optimal conditions in the metallization of polymers using the cold spray technique

Sull’utilizzo dell’energia cinetica per produzione additiva: primi risultati di prove di fatica e confronto con lavorazioni SLM

Il cold spray (CS) è una tecnica di rivestimento a freddo in cui la deposizione delle polveri avviene grazie all’impatto ad alta velocità delle particelle contro un substrato e alla conseguente elevata deformazione plastica, con l’instaurarsi delle condizioni di instabilità adiabatica di taglio. Nel presente lavoro sono stati considerati provini in In718 prodotti con CS e con SLM, sottoposti a diversi trattamenti termici, a valle della lavorazione dei provini. La caratterizzazione dei provini ha compreso l’analisi microstrutturale, la misura degli sforzi residui e della la porosità, mentre le prove meccaniche hanno previsto prove di trazione statiche e di fatica assiale. I risultati mostrano caratteristiche e resistenza comparabili a quelle dei provini SLM, suggerendo che il CS, grazie alla minore temperatura del processo e al ridotto impegno energetico, possa divenire una tecnologia additiva alternativa o complementare rispetto alle più consolidate tecnologie laser

Effects of hybrid post-treatments on fatigue behaviour of notched LPBF AlSi10Mg: Experimental and deep learning approaches

Laser powder bed fusion (LPBF) as one of the widely used technologies of additive manufacturing (AM), has a high capability to produce complex geometries such as notched parts in a layer-by-layer manner. LPBF parts in their as built state have inhomogeneous and anisotropic microstructure and poor surface quality. Post-treatments can play a key role in modulating these imperfections. In this study, the effects of four different post-treatments including heat treatment, shot peening and electro-chemical polishing as well as their combination as hybrid treatment were investigated on microstructure, surface and mechanical properties and finally fatigue behaviour of the LPBF V-notched AlSi10Mg samples. Afterward, a deep learning based approach was employed for modelling the fatigue behaviour via artificial neural network. Surface roughness, surface modification factor, hardness, residual stress and porosities were considered as inputs and fatigue life was considered as the output. Model function of the network was generated and the relevant parametric and sensitivity analyses were performed. The results indicated the importance of surface related properties and the notable effect of the surface post-treatments in enhancing the fatigue performance of the LPBF material

Fatigue properties of nanocrystallized surfaces obtained by high energy shot peening

AbstractAn unconventional method of shot peening aimed to generation of a nanograined layer over the surface of specimens has been applied by means of the standard air blast equipment but using peening parameters essentially different from typical ones. Surface nanocrystallization is verified and affirmed through different experimental procedures. Rotating bending fatigue tests are performed to evaluate the effect of this high energy shot peening and the nanocrystallized layer on fatigue life. First series results are available and the other tests are still in progress

Adapting Shot Peening for Surface Texturing Using Customized Additive Manufactured Shots

Surface textures in engineering materials not only affect the reflective properties and aesthetics but if properly designed can modulate surface-related properties such as wettability, fatigue, wear, corrosion, and scratch resistance. Herein, a new surface texturing method is introduced based on the conventional shot peening process. Custom shots are designed, and their surface texturing capability is investigated on acrylonitrile butadiene styrene (ABS) polymer substrates. A finite-element model is developed to bombard the substrate using AISI 316 stainless steel customized shots. The generated unique textures are compared qualitatively by visual examination and quantitatively using the standard surface roughness parameters. As a proof of concept, preliminary experiments are performed using a candidate custom shot and a spherical shot to treat the ABS sheets. The results highlight the high potential of the shot peening technique paired with additive manufacturing for customizing the peening media to be used for surface texturing polymeric materials

fracture and microstructural study of bovine bone under mixed mode i ii loading

Abstract Understanding the fracture behavior and associated crack growth mechanism in bone material is an important issue for biomechanics and biomaterial researches. Fracture of bone often takes place due to complex loading conditions which result in combined tensile-shear (i.e. mixed mode) fracture mechanism. Several parameters such as loading type, applied loading direction relative to the bone axis, loading rate, age and etc., may affect the mixed mode fracture resistance and damage mechanism in such materials. In this research, a number of mixed mode I/II fracture experiments are conducted on bovine femur bone using a sub-sized test configuration called "compact beam bend (CBB)" specimen to investigate the fracture toughness of bone under different mode mixities. The specimen is rectangular beam containing a mid-edge crack that is loaded by a conventional three-point bend fixture. The results showed the dependency of bone fracture toughness on the state of mode mixity. The fracture surfaces of broken CBB specimens under different loading conditions were studied via scanning electron microscopy (SEM) observations. Fracture surface of all investigated cases (i.e. pure mode I, pure mode II and mixed mode I/II) exhibited smooth patterns demonstrating brittle fracture of bovine femur. The higher density of vascular channels and micro-cracks initiated in the weakened area surrounded by secondary osteons were found to be the main cause of the decreased bone resistance against crack growth and brittle fracture

Design and Analysis of Energy Absorbent Bioinspired Lattice Structures

The increasing demand for energy absorbent structures, paired with the need for more efficient use of materials in a wide range of engineering fields, has led to an extensive range of designs in the porous forms of sandwiches, honeycomb, and foams. To achieve an even better performance, an ingenious solution is to learn how biological structures adjust their configurations to absorb energy without catastrophic failure. In this study, we have attempted to blend the shape freedom, offered by additive manufacturing techniques, with the biomimetic approach, to propose new lattice structures for energy absorbent applications. To this aim we have combined multiple bio-inspirational sources for the design of optimized configurations under compressive loads. Periodic lattice structures are fabricated based on the designed unit cell geometries and studied using experimental and computational strategies. The individual effect of each bio-inspired feature has been evaluated on the energy absorbance performance of the designed structure. Based on the design parameters of the lattices, a tuning between the strength and energy absorption could be obtained, paving the way for transition within a wide range of real-life applicative scenarios

Design and analysis of energy absorbent bioinspired lattice structures

The increasing demand for energy absorbent structures, paired with the need for more efficient use of materials in a wide range of engineering fields, has led to an extensive range of designs in the porous forms of sandwiches, honeycomb, and foams. To achieve an even better performance, an ingenious solution is to learn how biological structures adjust their configurations to absorb energy without catastrophic failure. In this study, we have attempted to blend the shape freedom, offered by additive manufacturing techniques, with the biomimetic approach, to propose new lattice structures for energy absorbent applications. To this aim we have combined multiple bio-inspirational sources for the design of optimized configurations under compressive loads. Periodic lattice structures are fabricated based on the designed unit cell geometries and studied using experimental and computational strategies. The individual effect of each bio-inspired feature has been evaluated on the energy absorbance performance of the designed structure. Based on the design parameters of the lattices, a tuning between the strength and energy absorption could be obtained, paving the way for transition within a wide range of real-life applicative scenarios

Surgical treatment of chronic patellar tendon rupture: A case series study

Background: Early detection and treatment of extensor mechanism rupture are essential for a long-term functional knee joint. In chronic cases, quadriceps muscle retraction and contracture make surgery di cult and results are less predictable. Objectives: The purpose of this study was to evaluate outcomes in the cases of late repaired patellar tendon rupture. Methods: This study included patients with chronic patellar tendon rupture who were operated at Shafa orthopedic hospital from 2006 to 2013. Results: A total of ten patients were evaluated, wirh 12 cases of chronic patellar tendon rupture. Patients had a mean age of 34.4 years (range 18 - 58). Seven cases were caused by a traffic accident and three by a fall. The mean length of time from injury to surgery was 23 months (range 3 - 132). The mean time of follow-up was 6.2 years (range 3 - 9). Cerclage wire reinforcements were applied in nine of the knees and three knees had fiber wire reinforcement. Tendon graft augmentation was applied in ten of the knees; six with semitendinosus and gracilis autograft, two with semitendinosus autograft, one with an Achilles tendon allograft, and one with a tibialis anterior allograft. Means for preoperative/postoperative active knee range of motion, extension lag, subjective international knee documentation committee score, and modified Cincinnati scores were 81/117, 32/2, 22.7/84.5 and 24/87, respectively. Wire breakage was seen on all nine knees but wires were removed in only two symptomatic cases. Conclusions: Good to excellent results were obtained in terms of functioning with operative treatment of chronic patellar tendon rupture. Direct repair with autogenous or allogenic graft augmentation and cerclage wire reinforcement and postoperative cast immobilization are recommended. Copyright © 2018, Trauma Monthly

Numerical modelling of grain refinement around highly reactive interfaces in processing of nanocrystallised multilayered metallic materials by duplex technique

Microstructure evolution around highly reactive interfaces in processing of nanocrystallised multilayered metallic materials have been investigated and discussed in the present work. Conditions leading to grain refinement during co-rolling stage of the duplex processing technique are analysed using the multi-level finite element based numerical model combined with three-dimensional frontal cellular automata. The model was capable to simulate development of grain boundaries and changes of the boundary disorientation angle within the metal structure taking into account crystal plasticity formulation. Appearance of a large number of structural elements, identified as dislocation cells, sub-grains and new grains, has been identified within the metal structure as a result of metal flow disturbance and consequently inhomogeneous deformation around oxide islets at the interfaces during the co-rolling stage. These areas corresponded to the locations of shear bands observed experimentally using SEM-EBSD analysis. The obtained results illustrate a significant potential of the proposed modelling approach for quantitative analysis and optimisation of the highly refined non-homogeneous microstructures formed around the oxidised interfaces during processing of such laminated materials