Increasing the structural energy dissipation of laminated fibre composite materials by delamination control

Publication date: 15 October 2018
Source:Materials & Design, Volume 156
Author(s): M. Kuhtz, A. Hornig, J. Richter, M. Gude
In this paper an approach to increase the energy absorption capacity of laminated composites is investigated. The interlaminar interfaces of two different composite materials, a 2/2 twill weave of glass fibre reinforced polypropylene and a plain weave of carbon reinforced epoxy, are modified. Perforated, non adhesive polytetrafluorethylene (PTFE-) foils were interleaved between the composite layers leading to different interlaminar contact area (ICA) set-ups. The energy absorption capacity, impact resistance as well as the damage and failure behaviour, especially delamination, are evaluated in Charpy drop weight experiments. Based on the resulting force-displacement-response, initiation and propagation energies as well as the ductility index are evaluated. High speed camera imaging is used to correlate failure phenomena to structural response. It can be shown, that the failure behaviour of textile reinforced composites is significantly influenced by the interface modification concept. As a result, the delamination initiation and propagation is enhanced with lower ICA leading to higher energy absorption capacity on the one hand and higher propagation-to-initiation-energy-ratio on the other hand. Consequently, the already high energy absorption capacity of composite materials can be further increased up to 65% while the ductility index rises up to ten times.

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Mapping of axial plastic zone for roller bearing overloads using neutron transmission imaging

Publication date: 15 October 2018
Source:Materials & Design, Volume 156
Author(s): A. Reid, I. Martinez, M. Marshall, T. Minniti, S. Kabra, W. Kockelmann, T. Connolley, M. Mostafavi
Premature failure of wind turbine gearbox bearings is an ongoing concern for industry, with sudden overload events potentially contributing towards raceway damage, significantly hindering performance. Subsurface stresses generated along a line contact cause material yielding, and a probable crack initiation site. Currently, the ability to study subsurface plastic zone evolution using non-destructive techniques is limited. Neutron Bragg edge imaging is a novel technique, allowing for two-dimensional mapping of the Bragg edge broadening parameter, indicative of bulk plastic deformation. An experiment on the ENGIN-X strain scanning instrument, at the ISIS neutron source, UK, was setup for Bragg edge transmission imaging, to measure the effect of in situ loading on the raceway of a bearing, scaled-down from a traditional wind turbine gearbox bearing. Results demonstrate a strong correlation between load and the Bragg edge width, and allow for future experimental development in studying, not only the effect of overloads on fatigue life, but also the use of neutron imaging for evaluating plastic deformation in engineering components.

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Enhancement of hardness, modulus and fracture toughness of the tetragonal (Fe,Cr)2B and orthorhombic (Cr,Fe)2B phases with addition of Cr

Publication date: 15 October 2018
Source:Materials & Design, Volume 156
Author(s): Jonathan Lentz, Arne Röttger, Felix Großwendt, Werner Theisen
This study analyzes the influence of Cr content on hardness H, elastic modulus E and fracture toughness KIC of the M2B boride by means of nanoindentation experiments. Additionally, properties of the Fe3(C,B) phase are determined. Samples of the M2B phase are casted and microstructurally characterized by means of scanning electron microscopy, energy dispersive spectroscopy and X-ray diffraction. At a Cr content higher than 14.7 atom% the M2B phase transforms from tetragonal into orthorhombic structure. The tetragonal M2B type possesses an optimum of H (21 ± 1 GPa), E (373 ± 6) GPa and KIC (3.5 ± 0.7 MPam) at 4–5 atom% Cr. The hardness, modulus and toughness of the orthorhombic M2B phase increase with Cr content and reach values of H = 27 ± 0.7 GPa, E = 473 ± 9 of and KIC = 3.26 ± 0.8 MPam at maximal investigated Cr content of 55 atom%. The hardness of the M2B phases decreases around 2.3–3.2 GPa as a function of indentation depth, which is known as the indentation size effect. Hardness and fracture toughness of M2B phase outperform conventionally used M7C3 carbides and are similar to MC-carbides. Findings can be used in novel alloying approaches in order to optimize the performance and reduce cost of tool steels.

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Thermal and tensile properties of diamondene at finite temperature: A molecular dynamics study

Publication date: 15 October 2018
Source:Materials & Design, Volume 156
Author(s): Jiao Shi, Kun Cai, Yi Min Xie
Diamondene can be formed by compressing two or more layers of graphene. As a sp²/sp³ orbital hybridized two-dimensional material, its physical properties are different from either graphene or diamond. This new material is ultrahard on a SiC substrate. Here, we focus on the thermal stability and the basic mechanical properties of diamondene without passivation. We used molecular dynamics calculations to show that diamondene has isotropic thermal expansion at temperature below 280 K. At room temperature, it is unstable. When stretched along the armchair direction, diamondene has a maximum elastic strain that is higher than 0.17. It then experiences further plastic deformation before collapse. However, when stretched along the zigzag direction, the maximum elastic strain is higher than 0.3, e.g., 0.318 at 250 K. The ribbon collapses soon after the strain exceeds the critical value. Hence, diamondene has an elastic-brittle property along the zigzag direction. This excellent elasticity is significant for applications of diamondene in a flexible device.

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Polymer-metal-polymer (PMP) multilayer transparent electrode for organic optoelectronics

Publication date: 15 October 2018
Source:Materials & Design, Volume 156
Author(s): Vikas Sharma, Himanshu Sharma, Rishi Vyas, Kanupriya Sachdev
Metal embedded polymer hybrid materials have found a niche of applications in energy and display domain. Herein, we report results of investigations on Polystyrene-Silver-Polystyrene (PAP) multilayer structure (<100 nm) exhibiting promising electrical and optical properties useful for the organic transparent electrode. Polystyrene and silver layers were obtained by spin coating and DC sputtering, respectively. Ag layer thickness was varied (4 nm to 30 nm) to optimize optical and electronic properties. Highest average transparency towards visible light was measured ≥70% for 8 nm thick Ag layered PAP structure whereas a minimum value of resistivity 6.03E−5 Ω was obtained for 12 nm thick Ag layer which implies the formation of the uniform continuous layer at this thickness. The study is supplemented with the characterization to prove smooth top layer which is required for growth of secondary layers (FESEM), chemical state of the trilayer (XPS measurement), uniformity in the chemical composition of the trilayer (Depth profiling) and structural properties (X-Ray diffraction and Raman spectroscopy). The importance of the present investigation lies in the synthesis process which is easy, low cost and allows tuning of optoelectronic properties of TCE as required by the application.

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Parvalbumin Interneurons Shape Neuronal Vulnerability in Blunt TBI

Abstract

Excessive excitation has been hypothesized to subsume a significant part of the acute damage occurring after traumatic brain injury (TBI). However, reduced neuronal excitability, loss of neuronal firing, and a disturbed excitation/inhibition balance have been detected. Parvalbumin (PV) interneurons are major regulators of perisomatic inhibition, principal neurons firing, and overall cortical excitability. However, their role in acute TBI pathogenic cascades is unclear. We exploited the chemogenetic Pharmacologically Selective Activation Module and Pharmacologically Selective Effector Module control of PV-Cre⁺ neurons and the Designer Receptors Exclusively Activated by Designer Drug (DREADD) control of principal neurons in a blunt model of TBI to explore the role of inhibition in shaping neuronal vulnerability to TBI. We demonstrated that inactivation of PV interneurons at the instance or soon after trauma enhances survival of principal neurons and reduces gliosis at 7 dpi whereas, activation of PV interneurons decreased neuronal survival. The protective effect of PV inactivation was suppressed by expressing the nuclear calcium buffer PV-nuclear localisation sequence in principal neurons, implying an activity-dependent neuroprotective signal. In fact, protective effects were obtained by increasing the excitability of principal neurons directly using DREADDs. Thus, we show that sustaining neuronal excitation in the early phases of TBI may reduce neuronal vulnerability by increasing activity-dependent survival, while excess activation of perisomatic inhibition is detrimental to neuronal integrity.

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Spreading of Tau Pathology in Sporadic Alzheimer’s Disease Along Cortico-cortical Top-Down Connections

Abstract

By using AT8-immunocytochemistry that visualizes hyperphosphorylated tau protein, we examined neurofibrillary changes related to sporadic Alzheimer's disease (AD) in N = 40 individuals at neurofibrillary tangle (NFT) stages I–IV. We report the presence of abnormal tau changes within solitary pyramidal neurons in layers III and V of the neocortex. These pyramidal cells showed pathology in different cell compartments (dendritic, somatic, axonal) that appeared to occur sequentially: Tau pathology was seen in distal segments of the basal dendrites, then in proximal dendrites, the soma, and, finally, in the axon of affected neurons. These findings are remarkable in that they point to the existence of neurofibrillary changes in regions routinely associated with later NFT stages. In addition, they lend support to the idea that it may be the axons of cortico-cortical top-down neurons in neocortical fields involved in AD that carry and spread abnormal tau seeds in a focused manner (transsynaptically) into the distal dendritic segments of nerve cells following directly in the neuronal chain, thereby sustaining further tau-seeded templating.

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