Hydrogen Assisted Fracture of 30MnB5 High Strength Steel: A Case Study

When steel components fail in service due to the intervention of hydrogen assisted cracking, discussion of the root cause arises. The failure is frequently blamed on component design, working conditions, the manufacturing process, or the raw material. This work studies the influence of quench and tempering and hot-dip galvanizing on the hydrogen embrittlement behavior of a high strength steel. Slow strain rate tensile testing has been employed to assess this influence. Two sets of specimens have been tested, both in air and immersed in synthetic seawater, at three process steps: in the delivery condition of the raw material, after heat treatment and after heat treatment plus hot-dip galvanizing. One of the specimen sets has been tested without further manipulation and the other set has been tested after applying a hydrogen effusion treatment. The outcome, for this case study, is that fracture risk issues only arise due to hydrogen re-embrittlement in wet service

Mechanical and microstructural features of plasma cut edges in a 15 mm thick S460M steel plate

In general, the thermal cutting processes of steel plates are considered to have an influence on microstructures and residual stress distribution, which determines the mechanical properties and performance of cut edges. They also affect the quality of the surface cut edges, which further complicates the problem, because in most cases the surface is subjected to the largest stresses. This paper studies the influence of plasma cutting processes on the mechanical behavior of the cut edges of steel and presents the characterization results of straight plasma arc cut edges of steel plate grade S460M, 15 mm thick. The cutting conditions used are the standard ones for industrial plasma cutting. The metallography of CHAZ (Cut Heat Affected Zones) and hardness profiles versus distance from plasma cut edge surface are tested; the mechanical behavior of different CHAZ layers under the cut edge surface were obtained by testing of instrumented mini-tensile 300 µm thick specimens. Also, the residual stress distribution in the CHAZ was measured by X-ray diffraction. The results for the mechanical properties, microstructure, hardness, and residual stresses are finally compared and discussed. This work concludes that the CHAZ resulting from the plasma cutting process is narrow (about 700 µm) and homogeneous in plate thickness

Molecular and Cellular Mechanisms of Delayed Fracture Healing in Mmp10 (Stromelysin 2) Knockout Mice

The remodeling of the extracellular matrix is a central function in endochondral ossification and bone homeostasis. During secondary fracture healing, vascular invasion and bone growth requires the removal of the cartilage intermediate and the coordinate action of the collagenase matrix metalloproteinase (MMP)-13, produced by hypertrophic chondrocytes, and the gelatinase MMP-9, produced by cells of hematopoietic lineage. Interfering with these MMP activities results in impaired fracture healing characterized by cartilage accumulation and delayed vascularization. MMP-10, Stromelysin 2, a matrix metalloproteinase with high homology to MMP-3 (Stromelysin 1), presents a wide range of putative substrates identified in vitro, but its targets and functions in vivo and especially during fracture healing and bone homeostasis are not well defined. Here, we investigated the role of MMP-10 through bone regeneration in C57BL/6 mice. During secondary fracture healing, MMP-10 is expressed by hematopoietic cells and its maximum expression peak is associated with cartilage resorption at 14 days post fracture (dpf). In accordance with this expression pattern, when Mmp10 is globally silenced, we observed an impaired fracture-healing phenotype at 14 dpf, characterized by delayed cartilage resorption and TRAP-positive cell accumulation. This phenotype can be rescued by a non-competitive transplant of wild-type bone marrow, indicating that MMP-10 functions are required only in cells of hematopoietic linage. In addition, we found that this phenotype is a consequence of reduced gelatinase activity and the lack of proMMP-9 processing in macrophages. Our data provide evidence of the in vivo function of MMP-10 during endochondral ossification and defines the macrophages as the lead cell population in cartilage removal and vascular invasio

Encapsulation of MSCs and GDNF in an Injectable Nanoreinforced Supramolecular Hydrogel for Brain Tissue Engineering

The co-administration of glial cell line-derived neurotrophic factor (GDNF) and mesenchymal stem cells (MSCs) in hydrogels (HGs) has emerged as a powerful strategy to enhance the efficient integration of transplanted cells in Parkinson's disease (PD). This strategy could be improved by controlling the cellular microenvironment and biomolecule release and better mimicking the complex properties of the brain tissue. Here, we develop and characterize a drug delivery system for brain repair where MSCs and GDNF are included in a nanoparticle-modified supramolecular guest-host HA HG. In this system, the nanoparticles act as both carriers for the GDNF and active physical crosslinkers of the HG. The multifunctional HG is mechanically compatible with brain tissue and easily injectable. It also protects GDNF from degradation and achieves its controlled release over time. The cytocompatibility studies show that the developed biomaterial provides a friendly environment for MSCs and presents good compatibility with PC12 cells. Finally, using RNA-sequencing (RNA-seq), we investigated how the three-dimensional (3D) environment, provided by the nanostructured HG, impacted the encapsulated cells. The transcriptome analysis supports the beneficial effect of including MSCs in the nanoreinforced HG. An enhancement in the anti-inflammatory effect of MSCs was observed, as well as a differentiation of the MSCs toward a neuron-like cell type. In summary, the suitable strength, excellent self healing properties, good biocompatibility, and ability to boost MSC regenerative potential make this nanoreinforced HG a good candidate for drug and cell administration to the brain

Elasto-plastic behaviour of a columnar structure of nanocrystalline iron with sharp 〈011〉 fibre texture

We explore, using molecular dynamics (MD), the strength and mechanical stability at 298 K of pure bcc Fe with an oriented columnar nanostructure of long grains randomly distributed about 〈011〉 and average size ranging from 20 to 5 nm in the cross-section. According to the simulations, the tensile flow stress of such aligned nanostructure spans from 4 GPa to 6 GPa as grain size decreases from 20 nm to 5 nm. The axially oriented tilt boundaries are very stable to axial plastic elongations as large as 0.5 true total (elastoplastic) tensile strain. The structure shows an important Bauschinger effect in compression after tensile elongation, but remains stable for relatively large compressive deformations. However, moderate plastic transverse shear deformations, which promote shear-coupled tilt boundary migrations, destabilize it, by provoking grain growth and softening. Our simulations connect with real world materials: very fine wires obtained by large-strain drawing bcc metals or alloys develop a similar columnar structure of 〈110〉 axially oriented grains of nanometric cross section and extraordinary mechanical strength.J.G.S. and J.A. gratefully acknowledge support from the Interuniversity Attraction Poles (IAP), Programme P7/21, Project INTEMATE, funded by the Belgian State, Belgian Science Policy. Work on this topic arose from longstanding collaboration of Ceit with NV Bekaert SA, Belgium.Peer reviewe

Mechanical and morphological modulation of electrospun polymeric scaffolds for tissue engineering applications

Electrospinning technologies herald the arrival of a new era in which previously unthinkable scaffolds for tissue engineering applications will be solved efficiently. However, electrospinning techniques, like solution electrospinning and melt electrowriting are held down by fabrications parameters, technology limitations, and the application perse. The science of scaffolding fabrication seeks to mimic the extracellular matrix of a particular tissue in ways that mitigates the damage or enables its pathophysiological study. Thenceforce, scaffolds have the primordial role of not only supporting the cells, but to replicate as close as possible the native extracellular matrix, taking into consideration the biocompatibility, biodegradability, morphology and mechanical properties. The last two properties are pivotal in the scaffold ́s outcome, as cells communicate with the environment, and behave in response to external signals. In context of scaffolds ́ assembly, electrospinning fabrication parameters should be correctly modulated, to ensure an appropriate cellular environment. In this dissertation we attempt to tackle this concern relying on solution electrospinning and melt electrowriting techniques. As potential tissue engineering applications, the recreation of an artificial human trabecular meshwork and a skeletal muscle platform are developed. The mechanical and morphological requirements of each tissue are evaluated and fabrication parameters adapted. An in vitro human trabecular meshwork scaffold was developed and validated with human trabecular meshwork cells ́ behavioral studies. With the development of a perfusion bioreactor human trabecular meshwork cells react to medicaments inducing measurable pressure changes. Finally, an attempt for skeletal muscle platform was made. This first approach enabled us the optimization of the process for next attempts.Las tecnologías de electrospinning (electrohilado) han establecido una nueva era en la que permiten resolver de manera eficiente scaffolds (andamios o estructuras) para aplicaciones de ingeniería de tejidos que antes eran impensables. Sin embargo, las técnicas de electrospinning, como el solution electrospinning (electrohilado de solución) o el melt electrowriting (electroescritura de fusión), se ven limitadas por los parámetros de fabricación, las limitaciones tecnológicas y la propia aplicación. La ciencia de la fabricación de scaffolds busca imitar la matrix extracelular de un tejido particular de manera que se mitigue el daño o se facilite su estudio fisiopatológico. Por lo tanto, los scaffoldstienen el papel primordial no solo de soportar las células, sino de replicar lo más fielmente posible la matriz extracelular nativa, teniendo en cuenta la biocompatibilidad, la biodegradabilidad, la morfología y las propiedades mecánicas. Estas dos últimas propiedades son fundamentales para el resultado del scaffold, ya que las células se comunican con el entorno y se comportan en respuesta a señales externas. En el contexto del ensamblaje de scaffolds, los parámetros de fabricación del electrospinning deben modularse correctamente para garantizar un entorno celular adecuado. En esta disertación, intentamos abordar esta preocupación confiando en las técnicas de solution electrospinning and melt electrowriting. Como posibles aplicaciones de la ingenieria de tejidos, se desarrolla la recreación de una malla trabecular humana artificial y una plataforma de músculo esquelético. Se evalúan los requisitos mecánicos y morfológicos de cada tejido y se adaptan los parámetros de fabricación. Se ha fabricado un scaffold de malla trabecular humana y se ha validado con células de este mismo tejido, evaluando su crecimiento y comportamiento. Además, gracias al desarrollo de una plataforma de perfusión se han podido medir los cambios de presión generados por las células al sometarlas a distintos medicamentos. Finalmente, se ha desarrollado una plataforma para músculo esquelético que ha permitido la optimización del proceso para futuros estudios

Atomistic simulation of the elongation response of a <011> oriented columnar nano-grain bcc Fe polycrystalline sample

The tensile elongation of an oriented columnar nanocrystalline pure iron structure at a temperature of 300 K has been simulated by molecular dynamics (MD). The simulated sample contains 4.3 × 10 atoms and has been subject to free elongation along the axis common to the grains. Periodic boundary conditions have been assumed. The grains are randomly oriented around their common and the size of their cross section is about 10 nm. The stress–strain curve has been calculated up to 0.5 true strain. After elastic deformation and heterogeneous dislocation nucleation from the grain boundaries, it shows a peak stress of 8 GPa followed by a remarkably stable steady state with a flow stress of 5.15 GPa, where neither the crystallographic texture nor the grain structure show any important change despite the large plastic deformation imparted. Upon a strain reversal, a pronounced Bauschinger effect is then observed (−3.3 GPa compressive yield stress), followed by a hardening transient until the absolute level of the flow stress in compression reaches near the same value it had in tension when the unloading took place. The results of the MD simulation are discussed by comparison with experimental values of the strength and structural evolution of heavily drawn iron wires available in the bibliography.J.G.S. and J.A. gratefully acknowledge partial support for performing this work from the InterUniversity Attraction Poles (IAP) Programme P7/21 (Project INTEMATE), funded by the Belgian State, Belgian Science Policy.Peer Reviewe

Hydrogen Assisted Fracture of 30MnB5 High Strength Steel: A Case Study

When steel components fail in service due to the intervention of hydrogen assisted cracking, discussion of the root cause arises. The failure is frequently blamed on component design, working conditions, the manufacturing process, or the raw material. This work studies the influence of quench and tempering and hot-dip galvanizing on the hydrogen embrittlement behavior of a high strength steel. Slow strain rate tensile testing has been employed to assess this influence. Two sets of specimens have been tested, both in air and immersed in synthetic seawater, at three process steps: in the delivery condition of the raw material, after heat treatment and after heat treatment plus hot-dip galvanizing. One of the specimen sets has been tested without further manipulation and the other set has been tested after applying a hydrogen effusion treatment. The outcome, for this case study, is that fracture risk issues only arise due to hydrogen re-embrittlement in wet service

Mechanical and morphological modulation of electrospun polymeric scaffolds for tissue engineering applications

Electrospinning technologies herald the arrival of a new era in which previously unthinkable scaffolds for tissue engineering applications will be solved efficiently. However, electrospinning techniques, like solution electrospinning and melt electrowriting are held down by fabrications parameters, technology limitations, and the application perse. The science of scaffolding fabrication seeks to mimic the extracellular matrix of a particular tissue in ways that mitigates the damage or enables its pathophysiological study. Thenceforce, scaffolds have the primordial role of not only supporting the cells, but to replicate as close as possible the native extracellular matrix, taking into consideration the biocompatibility, biodegradability, morphology and mechanical properties. The last two properties are pivotal in the scaffold ́s outcome, as cells communicate with the environment, and behave in response to external signals. In context of scaffolds ́ assembly, electrospinning fabrication parameters should be correctly modulated, to ensure an appropriate cellular environment. In this dissertation we attempt to tackle this concern relying on solution electrospinning and melt electrowriting techniques. As potential tissue engineering applications, the recreation of an artificial human trabecular meshwork and a skeletal muscle platform are developed. The mechanical and morphological requirements of each tissue are evaluated and fabrication parameters adapted. An in vitro human trabecular meshwork scaffold was developed and validated with human trabecular meshwork cells ́ behavioral studies. With the development of a perfusion bioreactor human trabecular meshwork cells react to medicaments inducing measurable pressure changes. Finally, an attempt for skeletal muscle platform was made. This first approach enabled us the optimization of the process for next attempts.Las tecnologías de electrospinning (electrohilado) han establecido una nueva era en la que permiten resolver de manera eficiente scaffolds (andamios o estructuras) para aplicaciones de ingeniería de tejidos que antes eran impensables. Sin embargo, las técnicas de electrospinning, como el solution electrospinning (electrohilado de solución) o el melt electrowriting (electroescritura de fusión), se ven limitadas por los parámetros de fabricación, las limitaciones tecnológicas y la propia aplicación. La ciencia de la fabricación de scaffolds busca imitar la matrix extracelular de un tejido particular de manera que se mitigue el daño o se facilite su estudio fisiopatológico. Por lo tanto, los scaffoldstienen el papel primordial no solo de soportar las células, sino de replicar lo más fielmente posible la matriz extracelular nativa, teniendo en cuenta la biocompatibilidad, la biodegradabilidad, la morfología y las propiedades mecánicas. Estas dos últimas propiedades son fundamentales para el resultado del scaffold, ya que las células se comunican con el entorno y se comportan en respuesta a señales externas. En el contexto del ensamblaje de scaffolds, los parámetros de fabricación del electrospinning deben modularse correctamente para garantizar un entorno celular adecuado. En esta disertación, intentamos abordar esta preocupación confiando en las técnicas de solution electrospinning and melt electrowriting. Como posibles aplicaciones de la ingenieria de tejidos, se desarrolla la recreación de una malla trabecular humana artificial y una plataforma de músculo esquelético. Se evalúan los requisitos mecánicos y morfológicos de cada tejido y se adaptan los parámetros de fabricación. Se ha fabricado un scaffold de malla trabecular humana y se ha validado con células de este mismo tejido, evaluando su crecimiento y comportamiento. Además, gracias al desarrollo de una plataforma de perfusión se han podido medir los cambios de presión generados por las células al sometarlas a distintos medicamentos. Finalmente, se ha desarrollado una plataforma para músculo esquelético que ha permitido la optimización del proceso para futuros estudios

Susceptibilidad a la fragilización por hidrógeno de aceros de alta resistencia: comportamiento en ambientes marinos y modelización de patrones de agrietamiento

The use of high strength steels is increasing steadily due to the cost, weight and performance advantages they offer. As a drawback, these materials are sensitive to environmental hydrogen embrittlement processes that reduce drastically the working loads they can resist, what limits their spreading to many applications. Since this embrittlement is catalyzed by corrosion prevention strategies involving cathodic protection, seawater exposed structures are specially concerned for the attack of hydrogen. Thus, high strength steel use for wet applications must be carefully assessed. In this context, this thesis deals with the study of the hydrogen embrittlement susceptibility of industrial high strength steels for immersed service in mooring chains and bolted joints. Based on the slow strain rate tensile testing method, the influence of cathodic protection and water temperature has been studied for submerged mooring chain steel grades R4, R5 and bolt steel class 10.9. A finite difference modeling strategy for predicting the cracking pattern observed during the experimental work is proposed.El empleo de aceros de alta resistencia está en constante aumento debido a las ventajas que ofrecen en coste, peso y rendimiento. Como contrapartida, estos materiales son sensibles a procesos de fragilización ambiental por hidrógeno que reducen de forma drástica las cargas que pueden resistir en servicio, lo que limita su extensión a muchas aplicaciones. Teniendo en cuenta que esta fragilización se cataliza en presencia de estrategias de protección catódica contra la corrosión, las estructuras en contacto con agua marina están especialmente expuestas al ataque por hidrógeno. En consecuencia, el uso de aceros de alta resistencia en contacto con agua debe ser analizado con cautela. En este contexto, esta tesis estudia la susceptibilidad a la fragilización por hidrógeno de aceros de alta resistencia de uso industrial para cadenas de fondeo y uniones atornilladas sumergidas. Se ha estudiado la influencia del tipo de protección catódica y la temperatura del agua en aceros para cadena de grados R4, R5 y acero de tornillería de clase 10.9, aplicando el método de ensayo de tracción a baja velocidad de deformación. Los patrones de agrietamiento observados en el trabajo experimental se han modelizado mediante una estrategia de cálculo por diferencias finitas