Loss Of Mechanical Integrity Research Articles

Strain learning in protein-based mechanical metamaterials

Mechanical deformation of polymer networks causes molecular-level motion and bond scission that ultimately lead to material failure. Mitigating this strain-induced loss in mechanical integrity is a significant challenge, especially in the development of active and shape-memory materials. We report the additive manufacturing of mechanical metamaterials made with a protein-based polymer that undergo a unique stiffening and strengthening behavior after shape recovery cycles. We utilize a bovine serum albumin-based polymer and show that cyclic tension and recovery experiments on the neat resin lead to a ~60% increase in the strength and stiffness of the material. This is attributed to the release of stored length in the protein mechanophores during plastic deformation that is preserved after the recovery cycle, thereby leading to a "strain learning" behavior. We perform compression experiments on three-dimensionally printed lattice metamaterials made from this protein-based polymer and find that, in certain lattices, the strain learning effect is not only preserved but amplified, causing up to a 2.5× increase in the stiffness of the recovered metamaterial. These protein-polymer strain learning metamaterials offer a unique platform for materials that can autonomously remodel after being deformed, mimicking the remodeling processes that occur in natural materials.

Scaling up a hollow fibre adsorption unit for on-board CCS applications using a real gasoline engine exhaust

Decarbonising road transport using on-board carbon capture and storage (CCS) is challenged by inherent space and energy limitations. Thus, to be technically and economically viable, robust and compact carbon capture units need to be developed. Hence, in this work, a scaled up hollow fibre adsorption unit was tested downstream of a real 90:10 gasoline-ethanol engine exhaust gas to evaluate its CO2 capture performance after 100 adsorption–desorption cycles. The scaled up hollow fibre adsorption unit consisted of 37 four-channel hollow fibre adsorption units coated with a thin carbon xerogel layer, referred to as the CX-coated hollow fibre module (HFM). It should be noted that this is the first study to report the results of a HFM tested under real conditions over 100 adsorption–desorption cycles and is one of the few studies that reports the desorption step. Furthermore, despite the presence of CO, THC, NOx, and H2O in the exhaust gas, the CX-coated HFM exhibited high CO2 capture stability and mechanical integrity. This was evidenced through the CX-coated HFM obtaining and maintaining an average total capacity of 1.2 mmol/g over 100 adsorption–desorption cycles, and showing no visible signs of deterioration or a loss of mechanical integrity.

Understanding the Electrolyte Chemistry Induced Enhanced Stability of Si Anodes in Li-Ion Batteries based on Physico-Chemical Changes, Impedance, and Stress Evolution during SEI Formation

The volume expansion/contraction of Si-based anodes during electrochemical lithiation/delithiation cycles causes a loss in mechanical integrity and accrued instability of the solid electrolyte interphase (SEI) layer, culminating into capacity fade. Electrolyte additives like fluoroethylene carbonate (FEC) improve SEI stability, but the associated causes still under debate. This work reveals some of the roles of FEC via post-mortem observations/analyses, operando stress measurements and a comprehensive study of the impedance associated with the formation/evolution of SEI during lithiation/delithiation. Usage of 10 vol.% FEC as electrolyte additive leads to significant improvements in cyclic stability, Coulombic efficiency and facilitates smoother/compact/crack-free surface/SEI, in contrast to the cracked/pitted/uneven surface upon non-usage of FEC. Operando stress measurements during SEI formation reveal compressive stress development, followed by loss in mechanical integrity, upon non-usage of electrolyte additive, in contrast to insignificant stress development associated with SEI formation upon usage of FEC. The EIS model proposed here facilitates good fit with the impedance data at all states-of-charges, with the SEI resistance and capacitance exhibiting expected variations with cycling and the SEI resistance progressively decreasing with cycle number in the presence of FEC. By contrast, in the absence of FEC, severe fluctuations observed with the SEI resistance and capacitance indicate instability.

Facile and Scalable Development of High-Performance Carbon-Free Tin-Based Anodes for Sodium-Ion Batteries.

Tin (Sn)-based anodes for sodium (Na)-ion batteries possess higher Na-storage capacity and better safety aspects compared to hard carbon -based anodes but suffer from poor cyclic stability due to volume expansion/contraction and concomitant loss in mechanical integrity during sodiation/desodiation. To address this, the usage of nanoscaled electrode-active particles and nanoscaled-carbon-based buffers has been explored, but with compromises with the tap density, accrued irreversible surface reactions, overall capacity (for "inactive" carbon), and adoption of non-scalable/complex preparation routes. Against this backdrop, anode-active "layered" bismuth (Bi) has been incorporated with Sn via a facile-cum-scalable mechanical-milling approach, leading to individual electrode-active particles being composed of well-dispersed Sn and Bi phases. The optimized carbon-free Sn-Bi compositions, benefiting from the combined effects of "buffering" action and faster Na transport of Bi, to go with the greater Na-storage capacity and lower operating potential of Sn, exhibit excellent cyclic stability (viz., ∼83-92% capacity retention after 200 cycles at 1C) and rate capability (viz., no capacity drop from C/5 to 2C, with only ∼25% drop at 5C), despite having fairly coarse particles (∼5-10 μm). As proven by operando synchrotron X-ray diffraction and stress measurements, the sequential sodiation/desodiation of the components and, concomitantly, stress build-ups at different potentials provide "buffering" action even for such "active-active" Sn-Bi compositions. Furthermore, the overall stress development upon sodiation of Bi has been found to be significantly lower than that of Sn (by a factor of ∼3.8), which renders Bi promising as a "buffer" material, in general. Dissemination of such complex interplay between electrode-active components during electrochemical cycling also paves the way for the development of high-performance, safe, and scalable "alloying-reaction"-based anode materials for Na-ion batteries and beyond, sans the need for ultrafine/nanoscaled electrode particles or "inactive" nanoscaled-carbon-based "buffer" materials.

High-Resolution Nanoanalytical Insights into Particle Formation in SnO2/ZnO Core/Shell Nanowire Lithium-Ion Battery Anodes.

Tin oxide (SnO2)/zinc oxide (ZnO) core/shell nanowires as anode materials in lithium-ion batteries (LIBs) were investigated using a combination of classical electrochemical analysis and high-resolution electron microscopy to correlate structural changes and battery performance. The combination of the conversion materials SnO2 and ZnO is known to have higher storage capacities than the individual materials. We report the expected electrochemical signals of SnO2 and ZnO for SnO2/ZnO core/shell nanowires as well as unexpected structural changes in the heterostructure after cycling. Electrochemical measurements based on charge/discharge, rate capability, and electrochemical impedance spectroscopy showed electrochemical signals for SnO2 and ZnO and partial reversibility of lithiation and delithiation. We find an initially 30% higher capacity for the SnO2/ZnO core/shell NW heterostructure compared to the ZnO-coated substrate without the SnO2 NWs. However, electron microscopy characterization revealed pronounced structural changes upon cycling, including redistribution of Sn and Zn, formation of ∼30 nm particles composed of metallic Sn, and a loss of mechanical integrity. We discuss these changes in terms of the different reversibilities of the charge reactions of both SnO2 and ZnO. The results show stability limitations of SnO2/ZnO heterostructure LIB anodes and offer guidelines on material design for advanced next-generation anode materials for LIBs.

ID: 216940 Retrospective Analysis of Safety and Efficacy of Disc Allograft Supplementation for Discogenic Low Back Pain

Low back pain has a prevalence of 60-70% in industrialized countries, and combined with neck pain, they made up the third costliest medical condition in 2013, at an estimated 87.6 billion dollars in medical spending.1,2 Intervertebral disc disruption accounts for greater than 42% of the back pain population, making it the most common causative etiology.3 A vital function of the intervertebral disc is to absorb shock and vibrations from activities of daily living, which preserves the spinal structure. The sponginess of the disc is attributed to proteoglycans and its’ watered structure, creating hydraulic properties within the nucleus pulposus. The disc relies on subchondral bone for nutrient and waste transfer. With aging there is desiccation and loss of mechanical integrity, leading to further degeneration of the surrounding structures.1

Deformation and Stresses During Alkali Metal Alloying/Dealloying of Sn-Based Electrodes

Abstract Enhancement of energy density and safety aspects of Li-ion cells necessitate the usage of “alloying reaction”-based anode materials in lieu of the presently used intercalation-based graphitic carbon. This becomes even more important for the upcoming Na-ion battery system since graphitic carbon does not intercalate sufficient Na-ions to qualify as an anode material. Among the potential “alloying reaction” based anode materials for Li-ion batteries and beyond (viz., Na-ion, K-ion battery systems), Si and Sn have received the major focus; with the inherently ductile nature of Sn (as against the brittleness of Si) and the considerably better stability in the context of electrochemical Na-/K-storage, of late, tilting the balance somewhat in favor of Sn. Nevertheless, similar to Si and most other “alloying reaction”-based anode materials, Sn also undergoes volume expansion/contraction and phase transformations during alkali metal-ion insertion/removal. These cause stress-induced cracking, pulverization, delamination from current collector, accrued polarization and, thus, fairly rapid capacity fade upon electrochemical cycling. Unlike Si, the aforementioned loss in mechanical integrity is believed to be primarily caused by some of the deleterious first-order phase transformations and concomitant formation of brittle intermetallic phases during the alloying/de-alloying process. Against this backdrop, this review article focuses on aspects related to deformation, stress development and associated failure mechanisms of Sn-based electrodes for alkali-metal ion batteries; eventually establishing correlations between phase assemblage/transformation, stress development, mechanical integrity, electrode composition/architecture and electrochemical behavior.

Nano- to macro-scale structural, mineralogical, and mechanical alterations in a shale reservoir induced by exposure to supercritical CO2

Considering the importance of carbon neutrality, UCCUS which is underground carbon capture, utilization, and storage has been widely adopted to mitigate climate change. Studies are being conducted to improve this process, however, there is still a lack of knowledge on the multiscale physicochanical alterations that the storage reservoirs may endure due to the long-term exposure to supercritical CO2 (ScCO2). These changes happen from nano- to macro-scale in mineralogy and pore structures which will impact mechanical and petrophysical attributes of the host rock. Since unconventional shale reservoirs have become the target of CO2-EOR and CO2 storage, it is imperative to understand the long-term impact of these alterations due to ScCO2 exposure. This study coupled experimental and theoretical modeling to investigate continuous nano- to macro-scale changes in mechanical, mineralogical, and structural alterations in the Middle Bakken by exposing samples to ScCO2 for 3, 8, 16, 30 and 60 days. Qualitative analysis of electron micrographs pre and post exposure confirmed certain minerals have evolved while image processing showed a quantitative change in pore structures. Moreover, nanomechanical changes pre and post exposure were inspected via nanoindentation method. Furthermore, we assessed how mineral content was impacted during the exposure using X-ray diffraction analysis. Next, we adopted two rock physics models based on mechanical and mineralogical observations to upscale mechanical properties to the macro scale. Analyses of the results indicate that long-term ScCO2 exposure induces mineral dissolution, precipitation and the development of fractures in the host reservoir. Further, CO2 induced alterations can lead to long-term macro-scale weakening causing a loss in mechanical integrity of the Middle Bakken by decreasing its elastic modulus (DS model = –33 %, MT model = -30 %) and increasing its Poisson’s ratio (DS model = +38 %, MT model = +32 %). Overall, this study can provide new insights for a better design and implementation of UCCUS projects in shale reservoirs, most especially in the Middle Bakken and other similar formations, where a lack of understanding of these variations and project planning could lead to potential CO2 leakages and environmental hazards.

Managing the mechanical integrity of pressure equipment using a layers of protection framework and incorporating integrity operating windows

A requirement of performance based regulatory regimes for managing process safety is to demonstrate the adequacy of control measures for reducing the risk of a major incident so far as reasonably practical (SFARP). Loss of mechanical integrity allowing loss of primary containment (LOPC) is recognized as a possible initiating step for a major incident. Often LOPC results from the action of damage mechanisms such as corrosion that are able to degrade or destroy the mechanical integrity of the containment envelope of pressure equipment. LOPC, allowing a major incident, generally arises from human error in the form of a lack of recognition of a damage mechanism that should have been identified in a HAZOP or risk assessment and captured in a standard operating practice supported by relevant training. In this paper, a layers of protection framework is proposed for assessing the performance standards and performance indicators required of control measures to allow demonstration that likelihood of LOPC has been reduced SFARP, where LOPC has resulted from a damage mechanism such as corrosion. The context is the requirement to demonstrate adequacy of the practices used to assure the integrity of the containment envelope of pressure equipment required to prevent a major incident. The assessment includes examining the adequacy of inspection as a control measure including the RBI practice of using industry failure frequency databases to underpin the justification of an extension of inspection intervals. An improvement is proposed that recognizes the role of integrity operating windows (following API RP 584) for managing the process environment including providing evidence of control of the service conditions and recording excursions from nominal service conditions. Underpinning the proposed improvement is consideration of the contribution of human error to LOPC events and the need to recognize performance shaping factors that minimize error.

Assessing Mg/Si3N4 biodegradable nanocomposites for osteosynthesis implants with a focus on microstructural, mechanical, in vitro corrosion and bioactivity aspects

Magnesium-based biodegradable implant materials for the osteosynthesis process (fixation or stabilizing of a fractured bone) are on the verge of being used clinically. However, the rapid degradation of magnesium-based materials in the physiological environment results in a loss of mechanical integrity before the complete healing of the fracture site. To address this issue, the present study used Silicon Nitride (Si3N4) nanoparticles to improve the in-vitro degradation resistance along with the mechanical strength and ductility of Magnesium. The Si3N4 nanoparticles were homogeneously reinforced in the pure Magnesium matrix through the ultrasonic-assisted stir casting method. Moreover, the effect of Si3N4 nanoparticles on microstructure, mechanical, in-vitro corrosion and bioactivity response of Mg/Si3N4 nanocomposites was studied. Notably, the inclusion of 1.0 vol% Si3N4 nanoparticles increased tensile strength by 1.4 times and ductility by two times. In addition, the elastic modulus of Mg/Si3N4 nanocomposites is within the range of local cortical bone elastic modulus. In-vitro immersion experiments in simulated physiological fluids revealed a 2.2-fold reduction in degradation rate compared to pure Magnesium. Moreover, the addition of Si3N4 nanoparticles enhanced the in-vitro bioactivity, as the surface of the nanocomposites showed a high needle-like Ca–P apatite layer with a 1.41 Ca/P ratio of the deposited layer close to hydroxyapatite's Ca/P ratio (1.64). Overall, this study provides the basis for the fabrication of stable yet completely biodegradable Mg/Si3N4 nanocomposite bone implants for the osteosynthesis process.

Modified-polyaspartic acid derivatives as effective corrosion inhibitor for C1018 steel in 3.5% NaCl saturated CO2 brine solution

BackgroundCorrosion challenges in the oil transportation pipelines operations worldwide is a serious problem and can lead to accelerated corrosion rates, loss of mechanical integrity and catastrophic failure. The survey of the literature reveals that few polymers haven been investigated as sweet corrosion inhibitors when compared to other small nitrogen containing heterocyclic organic molecules. Previous studies indicate that polyaspartic acid has been used as corrosion inhibitor but are required in high concentrations to be effective. To improve the performance of polyaspartic acid and to enable it usage at low concentrations, two modified-polyaspartic acid derivatives poly(cysteaminoaspartamide (7) and poly(methionenoaspartamide (8) were successfully synthesized, characterized, and demonstrated as effective corrosion inhibitor for C1018 steel in 3.5% NaCl saturated CO2 brine solution. MethodsElectrochemical techniques such as open circuit potentials (OCP), linear polarization measurements (LPR), electrochemical impedance spectroscopy (EIS) and potentiodynamic polarization (PDP) were used to obtained kinetics and mechanistic data of the corrosion inhibition process in 3.5% NaCl saturated CO2 brine. Scanning electron microscopy (SEM) and atomic force microscopy (AFM) images confirmed the adsorption of the molecules on the steel surface. Significant findingsResults obtained indicate that the two synthesized polymers are effective CO2 corrosion inhibitors. The inhibition performance of 7 (92.7%) was more pronounced at low concentrations (25 ppm) than 8 (53.6%) as obtained from EIS results. The effect of longer immersion time (24 h) strengthens further the performance of both corrosion inhibitors to 99. 25% for 7 and 96.84% for 8, respectively. Surface characterization using SEM and AFM provided more evidence for the steel surface protection with the two polymers. Molecular modeling using density functional theory (DFT) and Monte Carlo simulations (MC) supported the experimental results. The implication of this study is the possibility of replacing conventional toxic small nitrogen containing heterocyclic organic molecules with non-toxic and cost-effective polymeric counterparts based on modified- polyaspartic acid as corrosion inhibitors for use in oil and gas industry.

Open-porous magnesium-based scaffolds withstand in vitro corrosion under cyclic loading: A mechanistic study.

The successful application of magnesium (Mg) alloys as biodegradable bone substitutes for critical-sized defects may be comprised by their high degradation rate resulting in a loss of mechanical integrity. This study investigates the degradation pattern of an open-porous fluoride-coated Mg-based scaffold immersed in circulating Hanks' Balanced Salt Solution (HBSS) with and without in situ cyclic compression (30 N/1 Hz). The changes in morphological and mechanical properties have been studied by combining in situ high-resolution X-ray computed tomography mechanics and digital volume correlation. Although in situ cyclic compression induced acceleration of the corrosion rate, probably due to local disruption of the coating layer where fatigue microcracks were formed, no critical failures in the overall scaffold were observed, indicating that the mechanical integrity of the Mg scaffolds was preserved. Structural changes, due to the accumulation of corrosion debris between the scaffold fibres, resulted in a significant increase (p < 0.05) in the material volume fraction from 0.52 ± 0.07 to 0.47 ± 0.03 after 14 days of corrosion. However, despite an increase in fibre material loss, the accumulated corrosion products appear to have led to an increase in Young's modulus after 14 days as well as lower third principal strain (εp3) accumulation (−91000 ± 6361 με and −60093 ± 2414 με after 2 and 14 days, respectively). Therefore, this innovative Mg scaffold design and composition provide a bone replacement, capable of sustaining mechanical loads in situ during the postoperative phase allowing new bone formation to be initially supported as the scaffold resorbs.

Numerical models of pressure-driven fluid percolation in rock salt: nucleation and propagation of flow pathways under variable stress conditions

Success of our ongoing energy transition largely depends on subsurface exploitation. The subsurface can act as a “battery” to store energy dense fluids such as hydrogen, or a “host” to sequester unwanted substances such as carbon dioxide or radioactive waste. On the other hand, these operations cause the subsurface pressure and/or temperature to change and induce various (or cyclical) loadings to the surrounding formations. Their operational safety crucially hinges upon the subsurface integrity. The most imminent risk is nucleation of cracks that can lead to loss of mechanical integrity. Unlike hydraulic fracturing in geoenergy applications where one deliberately initiates cracks at certain targets, we normally design a system to avoid fracturing. At the designing stage, we thus have no prior knowledge of crack initiation locations or propagation paths. And, the computational designing tools should be able to assess the fracturing risk without such prior knowledge. In this study, we compared three computational approaches that do not require prescribed crack geometries—the discrete element method, the lattice element method, and the variational phase-field approach—against percolation experiments on rock salt. The experimental results show different fracture propagation paths depending on the boundary loads. The fracture geometries were reasonably matched by all approaches despite some differences in path irregularities. While the variational phase-field approach predicts relatively regular fracture paths, the paths predicted by the discrete and the lattice element methods are more irregular. These irregularities may seem more comparable to intergrain failure in real rocks, but they are also necessary triggers for fracture initiation in the discrete and the lattice element methods. In contrast, the fracture initiation in the variational phase-field approach is a realization of the energy minimization in the system, and the grain level descriptions are absent in the current formulation. These findings highlight their predictive capabilities and gaps to be bridged between the grain and continuum scales for field-scale applications.

Effect of Wind Load on Performance of Photovoltaic (PV) Modules Available in Pakistan

Mechanical integrity of a Photovoltaic (PV) module plays a major role in its performance and electrical output. Mechanical loads which include loads produced by wind, snow, rain, and hail tend to degrade the performance of PV module by generating stresses and enhancing micro-cracks and defects. This research aims to investigate the impact of wind loads on the performance of PV modules, particularly the degradation in its power output. A load of 2400 Pa was applied as per international standards (ASTM E1830-15 and IEC-61215). A total of four PV module samples, of the same specifications with 60 W rated power, were initially subjected to solar flash testing and Electroluminescence (EL) imaging. This was followed by three cycles of mechanical load test. After the mechanical load tests, the modules were again subjected to solar flash testing and EL imaging and the results were compared. It was noted that static wind load degrades the mechanical integrity of photovoltaic modules in two ways; by aiding the propagation of existing cracks and initiating new cracks. This loss of mechanical integrity degraded the power output of PV module. Maximum drop of 2% in the power output and 0.27% in the efficiency was observed. In addition, the average increase of 3.37% in the series resistance was observed indicating decrease in performance.

Biodegradable magnesium alloys for orthopaedic applications.

ABSTRACTThere is increasing interest in the development of bone repair materials for biomedical applications. Magnesium (Mg)-based alloys have a natural ability to biodegrade because they corrode in aqueous media; they are thus promising materials for orthopaedic device applications in that the need for a secondary surgical operation to remove the implant can be eliminated. Notably, Mg has superior biocompatibility because Mg is found in the human body in abundance. Moreover, Mg alloys have a low elastic modulus, close to that of natural bone, which limits stress shielding. However, there are still some challenges for Mg-based fracture fixation. The degradation of Mg alloys in biological fluids can be too rapid, resulting in a loss of mechanical integrity before complete healing of the bone fracture. In order to achieve an appropriate combination of bio-corrosion and mechanical performance, the microstructure needs to be tailored properly by appropriate alloy design, as well as the use of strengthening processes and manufacturing techniques. This review covers the evolution, current strategies and future perspectives of Mg-based orthopaedic implants.

Fast decellularization process using supercritical carbon dioxide for trabecular bone

Decellularization is a process that consists on the removal of immunogenic cellular material from a tissue, so that it can be safely implanted as a functional and bioactive scaffold. Most decellularization protocols rely on the use of harsh chemicals and very long washing processes, leading to severe changes in the ultrastructure and loss of mechanical integrity. To tackle these challenges, supercritical carbon dioxide (scCO2) is herein proposed as an alternative methodology for assisting decellularization of porcine trabecular bone tissue and is combined, for the first time, with Tri(n-butyl) phosphate (TnBP). Histological and DNA analysis revealed that both TnBP and scCO2 were able to extract the DNA content from the scaffolds, being this effect more pronounced in treatments that used TnBP as a co-solvent. The combined protocol led to a decrease in DNA content by at least 90%, demonstrating the potential of this methodology and opening new possibilities for future optimizations.

Effect of sterilization on 3-point dynamic response to in vitro bending of an Mg implant

BackgroundThe aim of the study is to characterize a biomedical magnesium alloy and highlighting the loss of mechanical integrity due to the sterilization method. Ideally, when using these alloys is to delay the onset of degradation so that the implant can support body loads and avoid toxicological effects due to the release of metal ions into the body.MethodsStandardized procedures according to ASTM F-1264 and ISO-10993-5 were used, respecting detailed methodological controls to ensure accuracy and reproducibility of the results, this testing methodology is carried out in accordance with the monographs of the Pharmacopoeia for the approval of medical devices and obtaining a health registration. An intramedullary implant (IIM) manufactured in magnesium (Mg) WE43 can support loads of the body in the initial period of bone consolidation without compromising the integrity of the fractured area. A system with these characteristics would improve morbidity and health costs by avoiding secondary surgical interventions.ResultsAs a property, the fatigue resistance of Mg in aggressive environments such as the body environment undergoes progressive degradation, however, the autoclave sterilization method drastically affects fatigue resistance, as demonstrated in tests carried out under in vitro conditions. Coupled with this phenomenon, the relatively poor biocompatibility of Mg WE43 alloys has limited applications where they can be used due to low acceptance rates from agencies such as the FDA. However, Mg alloy with elements such as yttrium and rare earth elements (REEs) have been shown to delay biodegradation depending on the method of sterilization and the physiological solution used. With different sterilization techniques, it may be possible to keep toxicological effects to a minimum while still ensuring a balance between the integrity of fractured bone and implant degradation time. Therefore, the evaluation of fatigue resistance of WE43 specimens sterilized and tested in immersion conditions (enriched Hank’s solution) and according to ASTM F-1264, along with the morphological, crystallinity, and biocompatibility characterization of the WE43 alloy allows for a comprehensive evaluation of the mechanical and biological properties of WE43.ConclusionsThese results will support decision-making to generate a change in the current perspective of biomaterials utilized in medical devices (MDs), to be considered by manufacturers and health regulatory agencies. An implant manufactured in WE43 alloy can be used as an intramedullary implant, considering keeping elements such as yttrium-REEs below as specified in its designation and with the help of a coating that allows increasing the life of the implant in vivo.

Synergistic effect of deep ball burnishing and HA coating on surface integrity, corrosion and immune response of biodegradable AZ31B Mg alloys.

The fast degradation and consequent loss of mechanical integrity is a major problem of biodegradable Mg alloy, which limits its clinical viability. This paper presents the influence of a synergistic approach combining deep ball burnishing and hydroxyapatite (HA) coating on biomechanical integrity, degradation and immune response of Mg alloy (AZ31B). The burnishing resulted in smooth surface topography, increased hardness from 0.87 to 1.45GPa and induced microstructural disturbances with deformation twins/twin bands, which enabled formation of a dense and compact platelet-like crystals HA coating of 110μm thickness. Compared to the untreated and burnished specimens, the burnished + HA coated surface provided remarkably higher corrosion resistance as indicated by lower corrosion current density and smaller mass loss. HA coating and surface integrity enhancement by burnishing were predominantly responsible for improved corrosion resistance. HA coating on the burnished surface exhibited hydrophilic properties and adequate bonding strength. While the modified surfaces promoted cell growth, the burnished + HA surface outperformed in exhibiting less pro-inflammatory and high anti-inflammatory cytokines, demonstrating that the treated surfaces were not posing any threat to immune cells. The findings indicate that the synergistic surface treatment can be a viable means to enhance corrosion resistance and immune response of Mg alloys implants.

Stress Corrosion and Corrosion Fatigue of Biodegradable Mg-Zn-Nd-Y-Zr Alloy in In-Vitro Conditions

Mg alloys are attractive as a structural material for biodegradable implants due to their mechanical properties, biocompatibility and degradation capability in physiological environments. However, their accelerated corrosion degradation, coupled with their inherent sensitivity to stress corrosion, can cause premature failure and consequently loss of mechanical integrity. This study aims to evaluate the potential of a Mg-5% Zn alloy with up to 3% Nd as an implant material in terms of stress corrosion performance in in vitro conditions. Stress corrosion behavior was evaluated under static loading conditions using slow strain rate testing (SSRT) analysis and under low cycle corrosion fatigue (LCCF). Both the SSRT analysis and LCCF testing were carried out in a simulated physiological environment in the form of a phosphate-buffered saline (PBS) solution. The obtained results indicate that the addition of up to 3% Nd to Mg-5% Zn alloy did not have any substantial influence on the stress corrosion susceptibility, beyond the inherent different mechanical properties of the tested alloys. This was attributed to the limited effect of the Nd on the passivation layer and due to the fact that the secondary phases produced by the Nd additions—W-phase (Mg3(Nd,Y)2Zn3) and T-phase (Mg4(Nd,Y)Zn2)—did not create any substantial micro-galvanic effect.

Mechanical integrity of process installations : An assessment based on bow-ties

Research was carried out in an ammonia plant of OCI Nitrogen, located at the Chemelot site in Geleen, The Netherlands. It focuses on the development of process safety accident processes in which loss of mechanical integrity is one of the root causes. A significant share of the mechanical integrity scenarios originate from corrosion mechanisms which develop over a relatively long time period, possibly taking months, years or even longer before turning into an event. Based on an example, a failure mechanism is worked out and visualized using a bow tie. Bow-ties have shown a good visual representation of the 'early warnings' and the barriers in place. The monitoring of the 'early warnings' and barriers can provide information about the current probability of the scenario in order to intervene prematurely.