Automatic quantification of matrix cracking and fiber rotation by X-ray computed tomography in shear-deformed carbon fiber-reinforced laminates

The deformation and damage mechanisms of carbon fiber-reinforced epoxy laminates deformed in shear were studied by means of X-ray computed tomography. In particular, the evolution of matrix cracking, interply delamination and fiber rotation was ascertained as a function of the applied strain. In order to provide quantitative information, an algorithm was developed to automatically determine the crack density and the fiber orientation from the tomograms. The investigation provided new insights about the complex interaction between the different damage mechanisms (i.e. matrix cracking and interply delamination) as a function of the applied strain, ply thickness and ply location within the laminate as well as quantitative data about the evolution of matrix cracking and fiber rotation during deformation

Modelling of stiffness degradation due to cracking in laminates subjected to multi-axial loading

Funding Financial support of this research by the Engineering and Physical Sciences Research Council (EPSRC/GR/L51348) and the British Ministry of Defence is gratefully acknowledged.

Failure analysis of low velocity impact on thin composite laminates: Experimental and numerical approaches

The dynamic behavior of composite laminates is very complex because there are many concurrent phenomena during composite laminate failure under impact load. Fiber breakage, delaminations, matrix cracking, plastic deformations due to contact and large displacements are some effects which should be considered when a structure made from composite material is impacted by a foreign object. Thus, an investigation of the low velocity impact on laminated composite thin disks of epoxy resin reinforced by carbon fiber is presented. The influence of stacking sequence and energy impact was investigated using load-time histories, displacement-time histories and energy-time histories as well as images from NDE. Indentation tests results were compared to dynamic results, verifying the inertia effects when thin composite laminate was impacted by foreign object with low velocity. Finite element analysis (FEA) was developed, using Hill`s model and material models implemented by UMAT (User Material Subroutine) into software ABAQUS (TM), in order to simulate the failure mechanisms under indentation tests. (C) 2007 Elsevier Ltd. All rights reserved.

Ein Beitrag zur realitätsnahen Modellierung und Analyse von stahlfaserverstärkten Stahlbeton- und Stahlbetonflächentragwerken

Das Werkstoffverhalten von stahlfaserfreiem bzw. stahlfaserverstärktem Stahlbeton unter biaxialle Druck- Zugbeanspruchung wurde experimentell und theoretisch untersucht. Die Basis der experimentellen Untersuchungen waren zahlreiche Versuche, die in der Vergangenheit an faserfreiem Stahlbetonscheiben zur Bestimmung des Werkstoffverhaltens von gerissenem Stahlbeton im ebenen Spannungszustand durchgeführt wurden. Bei diesen Untersuchungen wurde festgestellt, dass infolge einer Querzugbeanspruchung eine Abminderung der biaxialen Druckfestigkeit entsteht. Unter Berücksichtigung dieser Erkenntnisse sind zur Verbesserung der Werkstoffeigenschaften des Betons, Stahlbetonscheiben aus stahlfaserverstärktem Beton hergestellt worden. Die aus der Literatur bekannten Werkstoffmodelle für Beton sowie Stahlbeton, im ungerissenen und gerissenen Zustand wurden hinsichtlich der in der Vergangenheit ermittelten Materialeigenschaften des Betons bzw. Stahlbetons unter proportionalen sowie nichtproportionalen äußeren Belastungen erklärt und kritisch untersucht. In den frischen Beton wurden Stahlfasern hinzugegeben. Dadurch konnte die Festigkeits- und die Materialsteifigkeitsabminderung infolge Rissbildung, die zur Schädigung des Verbundwerkstoffs Beton führt, reduziert werden. Man konnte sehen, dass der Druckfestigkeitsabminderungsfaktor und insbesondere die zur maximal aufnehmbaren Zylinderdruckfestigkeit gehörende Stauchung, durch Zugabe von Stahlfasern besser begrenzt wird. Die experimentelle Untersuchungen wurden an sechs faserfreien und sieben stahlfaserverstärkten Stahlbetonscheiben unter Druck-Zugbelastung zur Bestimmung des Verhaltens des gerissenen faserfreien und stahlfaserverstärkten Stahlbetons durchgeführt. Die aus eigenen Versuchen ermittelten Materialeigenschaften des Betons, des stahlfaserverstärkten Betons und Stahlbetons im gerissenen Zustand wurden dargelegt und diskutiert. Bei der Rissbildung des quasi- spröden Werkstoffs Beton und dem stahlfaserverstärkten Beton wurde neben dem plastischen Fließen, auch die Abnahme des Elastizitätsmoduls festgestellt. Die Abminderung der aufnehmbaren Festigkeit und der zugehörigen Verzerrung lässt sich nicht mit der klassischen Fließtheorie der Plastizität ohne Modifizierung des Verfestigungsgesetzes erfassen. Es wurden auf elasto-plastischen Werkstoffmodellen basierende konstitutive Beziehungen für den faserfreien sowie den stahlfaserverstärkten Beton vorgeschlagen. Darüber hinaus wurde in der vorliegenden Arbeit eine auf dem elasto-plastischen Werkstoffmodell basierende konstitutive Beziehung für Beton und den stahlfaser-verstärkten Beton im gerissenen Zustand formuliert. Die formulierten Werkstoffmodelle wurden mittels dem in einer modularen Form aufgebauten nichtlinearen Finite Elemente Programm DIANA zu numerischen Untersuchungen an ausgewählten experimentell untersuchten Flächentragwerken, wie scheibenartigen-, plattenartigen- und Schalentragwerken aus faserfreiem sowie stahlfaserverstärktem Beton verwendet. Das entwickelte elasto-plastische Modell ermöglichte durch eine modifizierte effektive Spannungs-Verzerrungs-Beziehung für das Verfestigungsmodell, nicht nur die Erfassung des plastischen Fließens sondern auch die Berücksichtigung der Schädigung der Elastizitätsmodule infolge Mikrorissen sowie Makrorissen im Hauptzugspannungs-Hauptdruckspannungs-Bereich. Es wurde bei den numerischen Untersuchungen zur Ermittlung des Last-Verformungsverhaltens von scheibenartigen, plattenartigen- und Schalentragwerken aus faserfreiem und stahlfaserverstärktem Stahlbeton, im Vergleich mit den aus Versuchen ermittelten Ergebnissen, eine gute Übereinstimmung festgestellt.

Modelización constitutiva y computacional del daño y la fractura de materiales compuestos

En el trabajo se definen modelos constitutivos que permiten reproducir el proceso de fallo de estructuras de materiales compuestos en distintas escalas bajo cargas estáticas. Se define un modelo constitutivo para determinar la respuesta de estructuras de materiales compuestos mediante la teoría de laminados. El modelo es validado mediante un programa de ensayos experimentales con probetas con un agujero central geométricamente similares. Se muestra la capacidad del modelo de detectar el efecto tamaño. Se define un modelo constitutivo para materiales transversalmente isótropos bajo estados tridimensionales de tensión. El modelo se valida analizando numéricamente el proceso de agrietamiento de la matriz. Finalmente se desarrolla un modelo analítico para determinar el agrietamiento de la matriz y la delaminación entre las capas.

Predicting residual stiffness of cracked composite laminates subjected to multi-axial in-plane loading

Peer reviewed

Predicting residual stiffness of cracked composite laminates subjected to multi-axial in-plane loading

Peer reviewed

Modelling the crush behaviour of thermoplastic composites

Thermoplastic composites are likely to emerge as the preferred solution for meeting the high-volume production demands of passenger road vehicles. Substantial effort is currently being directed towards the development of new modelling techniques to reduce the extent of costly and time consuming physical testing. Developing a high-fidelity numerical model to predict the crush behaviour of composite laminates is dependent on the accurate measurement of material properties as well as a thorough understanding of damage mechanisms associated with crush events. This paper details the manufacture, testing and modelling of self-supporting corrugated-shaped thermoplastic composite specimens for crashworthiness assessment. These specimens demonstrated a 57.3% higher specific energy absorption compared to identical specimen made from thermoset composites. The corresponding damage mechanisms were investigated in-situ using digital microscopy and post analysed using Scanning Electron Microscopy (SEM). Splaying and fragmentation modes were the 2 primary failure modes involving fibre breakage, matrix cracking and delamination. A mesoscale composite damage model, with new non-linear shear constitutive laws, which combines a range of novel techniques to accurately capture the material response under crushing, is presented. The force-displacement curves, damage parameter maps and dissipated energy, obtained from the numerical analysis, are shown to be in a good qualitative and quantitative agreement with experimental results. The proposed approach could significantly reduce the extent of physical testing required in the development of crashworthy structures.  

Influence of Microstructures on Polarization Resistance and Hydrogen-Induced Cracking of a Micro-Alloyed Steel Submitted to Different Cooling Rates

The effect of different microstructures on the polarization resistance (Rp) and the hydrogen-induced cracking (HIC) of a micro-alloyed steel austenitized and submitted to different cooling rates was studied. Samples 19.1 x 6 x 2 mm, containing the whole thickness of the plate were extracted from a 20 mm plate and heat treated on a quenching dilatometer, were submitted to Rp and HIC corrosion tests. Both Rp and HIC tests followed as close as possible ASTM G59 and NACE standard TM0284-2003, in this case, modified only with regard to the size of the samples. Steel samples transformed from austenite by a slow cooling (cooling rate of 0.5 degrees C.s(-1)) showed higher susceptibility to hydrogen-induced cracking, with large cracks in the middle of the sample propagating along segregation bands, corresponding to the centerline of the plate thickness. For cooling rates of 10 degrees C.s(-1), only small cracks were found in the matrix and micro cracks nucleated at non-metallic inclusions. For higher cooling rates (40 degrees C.s(-1)) very few small cracks were detected, linked to non-metallic inclusions. This result suggests that structures formed by polygonal structures and segregation bands (were cutectoid microconstituents predominate) have higher susceptibility to HIC. Structures predominantly formed by acicular ferrite make it difficult to propagate the cracks among non-oriented and interlaced acicular ferrite crystals. Smaller segregation bands containing eutectoid products also help inhibit cracking and crack propagation; segregation bands can function as pipelines for hydrogen diffusion and offer a path of stress concentration for the propagation of cracks, frequently associated to non-metallic inclusions. Polarization resistance essays performed on the steel in theas received condition, prior to any heat treatment, showed larger differences between the regions of the plate, with a considerably lower Rp in the centerline. The austenitization heat treatments followed by cooling rates of 0.5 e 10 degrees C.s(-1) made more uniform the corrosion resistance along the thickness of the plate. The effects of heat treatments on the corrosion resistance are probably related to the microconstituent formed, allied to the chemical homogenization of the impurities concentrated on the centerline of the plate.

Effect of microstructure and alloying elements on the resistance of fastener grade steels to hydrogen assisted cracking

Fastener grade steels with varying alloy contents and heat treatments were employed to measure changes in resistance to hydrogen assisted cracking. The testing procedure compared notched tension specimens fractured in air to threshold stress values obtained during hydrogen charging, utilizing a rising step load procedure. Bainitic structures improved resistance by 10-20% compared to tempered martensite structures. Dual phase steels with a tempered martensite matrix and 20% ferrite were more susceptible and notch sensitive. High strength, fully pearlitic structures showed an improvement in resistance. Carbon content, per se, had no effect on the resistance of steel to hydrogen assisted cracking. Chromium caused a deleterious effect but all other alloying elements studied did not cause much change in hydrogen assisted cracking susceptibility.

Quantitative Proteomic Analysis Reveals Metabolic Alterations, Calcium Dysregulation, And Increased Expression Of Extracellular Matrix Proteins In Laminin α2 Chain-deficient Muscle.

Congenital muscular dystrophy with laminin α2 chain deficiency (MDC1A) is one of the most severe forms of muscular disease and is characterized by severe muscle weakness and delayed motor milestones. The genetic basis of MDC1A is well known, yet the secondary mechanisms ultimately leading to muscle degeneration and subsequent connective tissue infiltration are not fully understood. In order to obtain new insights into the molecular mechanisms underlying MDC1A, we performed a comparative proteomic analysis of affected muscles (diaphragm and gastrocnemius) from laminin α2 chain-deficient dy(3K)/dy(3K) mice, using multidimensional protein identification technology combined with tandem mass tags. Out of the approximately 700 identified proteins, 113 and 101 proteins, respectively, were differentially expressed in the diseased gastrocnemius and diaphragm muscles compared with normal muscles. A large portion of these proteins are involved in different metabolic processes, bind calcium, or are expressed in the extracellular matrix. Our findings suggest that metabolic alterations and calcium dysregulation could be novel mechanisms that underlie MDC1A and might be targets that should be explored for therapy. Also, detailed knowledge of the composition of fibrotic tissue, rich in extracellular matrix proteins, in laminin α2 chain-deficient muscle might help in the design of future anti-fibrotic treatments. All MS data have been deposited in the ProteomeXchange with identifier PXD000978 (http://proteomecentral.proteomexchange.org/dataset/PXD000978).

Matrix Metalloproteinases And Left Ventricular Function And Structure In Spinal Cord Injured Subjects.

Subjects with spinal cord injury (SCI) exhibit impaired left ventricular (LV) diastolic function, which has been reported to be attenuated by regular physical activity. This study investigated the relationship between circulating matrix metalloproteinases (MMPs) and tissue inhibitors of MMPs (TIMPs) and echocardiographic parameters in SCI subjects and the role of physical activity in this regard. Forty-two men with SCI [19 sedentary (S-SCI) and 23 physically-active (PA-SCI)] were evaluated by clinical, anthropometric, laboratory, and echocardiographic analysis. Plasmatic pro-MMP-2, MMP-2, MMP-8, pro-MMP-9, MMP-9, TIMP-1 and TIMP-2 levels were determined by enzyme-linked immunosorbent assay and zymography. PA-SCI subjects presented lower pro-MMP-2 and pro-MMP-2/TIMP-2 levels and improved markers of LV diastolic function (lower E/Em and higher Em and E/A values) than S-SCI ones. Bivariate analysis showed that pro-MMP-2 correlated inversely with Em and directly with E/Em, while MMP-9 correlated directly with LV mass index and LV end-diastolic diameter in the whole sample. Following multiple regression analysis, pro-MMP-2, but not physical activity, remained associated with Em, while MMP-9 was associated with LV mass index in the whole sample. These findings suggest differing roles for MMPs in LV structure and function regulation and an interaction among pro-MMP-2, diastolic function and physical activity in SCI subjects.

Identification Of Corynebacterium Spp. Isolated From Bovine Intramammary Infections By Matrix-assisted Laser Desorption Ionization-time Of Flight Mass Spectrometry.

Corynebacterium species (spp.) are among the most frequently isolated pathogens associated with subclinical mastitis in dairy cows. However, simple, fast, and reliable methods for the identification of species of the genus Corynebacterium are not currently available. This study aimed to evaluate the usefulness of matrix-assisted laser desorption ionization/mass spectrometry (MALDI-TOF MS) for identifying Corynebacterium spp. isolated from the mammary glands of dairy cows. Corynebacterium spp. were isolated from milk samples via microbiological culture (n=180) and were analyzed by MALDI-TOF MS and 16S rRNA gene sequencing. Using MALDI-TOF MS methodology, 161 Corynebacterium spp. isolates (89.4%) were correctly identified at the species level, whereas 12 isolates (6.7%) were identified at the genus level. Most isolates that were identified at the species level with 16 S rRNA gene sequencing were identified as Corynebacterium bovis (n=156; 86.7%) were also identified as C. bovis with MALDI-TOF MS. Five Corynebacterium spp. isolates (2.8%) were not correctly identified at the species level with MALDI-TOF MS and 2 isolates (1.1%) were considered unidentified because despite having MALDI-TOF MS scores >2, only the genus level was correctly identified. Therefore, MALDI-TOF MS could serve as an alternative method for species-level diagnoses of bovine intramammary infections caused by Corynebacterium spp.

Inactivation Of Ampk Mediates High Phosphate-induced Extracellular Matrix Accumulation Via Nox4/tgfß-1 Signaling In Human Mesangial Cells.

High phosphate (Pi) levels and extracellular matrix (ECM) accumulation are associated with chronic kidney disease progression. However, how high Pi levels contribute to ECM accumulation in mesangial cells is unknown. The present study investigated the role and mechanism of high Pi levels in ECM accumulation in immortalized human mesangial cells (iHMCs). iHMCs were exposed to normal (0.9 mM) or increasing Pi concentrations (2.5 and 5 mM) with or without diferent blockers or activators. NOX4, phosphorylated AMPK (p-AMPK), phosphorylated SMAD3 (p-SMAD3), fibronectin (F/N), collagen IV (C-IV) and alpha-smooth muscle actin (α-SMA) expression was assessed via western blot and immunofluorescence. Lucigenin-enhanced chemiluminescence, and dihydroethidium (DHE) assessed NADPH oxidase activity and superoxide (SO), respectively. In iHMCs, a Pi transporter blocker (PFA) abrogated high Pi-induced AMPK inactivation, increase in NADPH oxidase-induced reactive oxygen species (ROS) levels, NOX4, p-SMAD3, α-SMA and C-IV expression. AMPK activation by AICAR, NOX4 silencing or NADPH oxidase blocker prevented high Pi-induced DHE levels, p-SMAD3, F/N, C-IV and α-SMA expression. AMPK inactivation with NOX4-induced ROS formation and transforming growth factor ß-1 (TGFß-1) signaling activation mediates high Pi-induced ECM accumulation in iHMCs. Maneuvers increasing AMPK or reducing NOX4 activity may contribute to renal protection under hyperphosphatemia.

A Metabolomic Protocol For Plant Systematics By Matrix-assisted Laser-desorption/ionization Time-of Flight Mass Spectrometry.

Matrix-assisted laser desorption/ionization time-of flight mass spectrometry (MALDI-TOF MS) has been widely used for the identification and classification of microorganisms based on their proteomic fingerprints. However, the use of MALDI-TOF MS in plant research has been very limited. In the present study, a first protocol is proposed for metabolic fingerprinting by MALDI-TOF MS using three different MALDI matrices with subsequent multivariate data analysis by in-house algorithms implemented in the R environment for the taxonomic classification of plants from different genera, families and orders. By merging the data acquired with different matrices, different ionization modes and using careful algorithms and parameter selection, we demonstrate that a close taxonomic classification can be achieved based on plant metabolic fingerprints, with 92% similarity to the taxonomic classifications found in literature. The present work therefore highlights the great potential of applying MALDI-TOF MS for the taxonomic classification of plants and, furthermore, provides a preliminary foundation for future research.