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We experimentally determined the uniaxial compressive stress-strain responses of an auxetic polyurethane (PU) foam at quasi-static (0.01/s), intermediate (1/s, 10/s and 745/s) and high (1430/s, 1870/s and 2290/s) strain rates. A hydraulically driven materials testing system (MTS) was used to perform the experiments at the strain rate of 0.1/s, 1/s and 10/s, while higher intermediate (745/s) and high strain-rate compressive loadings were introduced using long and regular Kolsky bars, respectively. The Poisson effect of the auxetic PU foam was also investigated during the experiments using a precision LED optical micrometer system (OMS) (0.01/s–10/s) or an ultra-high speed camera (745/s–2290/s). Our results show that the compressive stress-strain curves of the auxetic PU foam are non-linear and strain-rate sensitive. In all the experiments, the Poisson's ratio, with an initial negative value at small strains, progressively increased toward 0 as the specimen was further compressed. The strain-rate effect on the material's Poisson's ratio is also evident in our study, as the specimens subjected to high strain-rate loadings exhibited smaller negative Poisson's ratios (NPR) in absolute sense at small strains in comparing with those at quasi-static and intermediate strain rates.

Compassion fatigue can negatively affect not only healthcare professionals' physical and mental health but also the quality of care they provide and organizational outcomes. However, little is known about compassion fatigue among Chinese midwives working in the delivery room. This study aimed to examine compassion fatigue and compassion satisfaction levels among Chinese midwives working in the delivery room and correlate their compassion fatigue and compassion satisfaction.A multisite cross-sectional study with a convenience sampling approach was conducted at 62 hospitals in Henan Province, central China, from May to July 2020. The participants were recruited through an online survey. A self-designed sociodemographic and work-related data sheet, the Social Support Rating Scale (SSRS), and the Professional Quality of Life Scale (ProQoL) were used to measure the participants'basic information, level of social support, compassion fatigue(consists of burnout and secondary traumatic stress) and compassion satisfaction. Descriptive analysis was used to describe the characteristics of the participants' social support, compassion fatigue and compassion satisfaction. Multiple linear regression analysis was employed to identify associations with the participants' sociodemographic and professional characteristics, compassion fatigue and compassion satisfaction.A total of 213 questionnaires were completed, 206 of which were valid (96.71%). The majority of the participants reported moderate risks for compassion satisfaction (75.24%) and burnout (59.71%) and low risks for secondary traumatic stress (61.65%). Higher job satisfaction as a midwife, lower average working hours per week in the past year, higher social support, extroverted personality, and work recognition in the past month were positively associated with compassion satisfaction, explaining 48.7% of the total variance. Always considering giving up a midwifery career, lower social support, working a day-night shift, poor health condition, more exposure to traumatic birth events per month on average in recent years, and lower job satisfaction as a midwife were negative factors for burnout, explaining 35.3% of the total variance. Four factors, including more exposure to traumatic birth events per month on average in recent years, always considering giving up a midwifery career, working a day-night shift and poor sleep quality, were negatively related to secondary traumatic stress, explaining 14.2% of the variance.In this study, midwives showed moderate levels of compassion satisfaction and burnout and low levels of secondary traumatic stress which should attract the attention of health institutions. A healthy and supportive work environment is crucial to midwives' health, well-being and job satisfaction. Tailored strategies such as trauma management, emotional literacy, peer and social support networks should be implemented to support midwives' compassion satisfaction, while prevent and lower midwives' burnout and secondary traumatic stress.

Background The “secondary injury” theory of liver failure indicated that hyperammonaemia due to liver failure causes further deterioration of hepatocytes. Our previous studies have demonstrated that high blood ammonia levels may lead to hepatocyte apoptosis, as NH4Cl loading caused metabolic acidosis and an increase in sodium-hydrogen exchanger isoform 1 (NHE1). In this study, we established a hyperammonia hepatocyte model to determine the role of NHE1 in the regulation of hepatocyte apoptosis induced by NH4Cl. Materials and methods In current studies, intracellular pH (pHi) and NHE1 activity were analyzed using the pHi-sensitive dye BCECF-AM. The results showed that intracellular pH dropped and NHE1 activity increased in hepatocytes under NH4Cl treatment. As expected, decreased pHi induced by NH4Cl was associated with increased apoptosis, low cell proliferation and ATP depletion, which was exacerbated by exposure to the NHE1 inhibitor cariporide. We also found that NH4Cl treatment stimulated PI3K and Akt phosphorylation and this effect was considerably reduced by NHE1 inhibition. Conclusion This study highlighted the significant role of NHE1 in the regulation of cell apoptosis induced by hyperammonaemia.

This paper demonstrates the effectiveness of parametrically-upscaled continuum damage mechanics (PUCDM) models for multiscale damage analysis of S-2 glass fiber/SC-15 epoxy matrix composite beams subjected to single-edge notched bending (SENB) tests. The SENB experiments with [ 0 12 / 9 0 12 ] double-ply and [ 0 8 / 9 0 8 / 0 8 ] triple-ply composite beams use synchrotron X-ray phase-contrast imaging for in-situ damage characterization. PUCDM models represent a class of thermodynamically-consistent multiscale constitutive models that bridge length-scales through explicit incorporation of representative aggregated microstructural parameters (RAMPs) in constitutive coefficients. Functional forms of RAMPs are generated through machine learning tools, operating on a micromechanical analysis database. The efficient PUCDM-based FE simulations reveal multiscale damage phenomena in the SENB experiments.

Environmental chemicals inhalation exposure could induce pulmonary fibrosis, which is characterized by the excessive proliferation of fibroblasts and accumulation of extracellular matrix components, in which surface tension usually plays vital roles. Polyhexamethylene guanidine (PHMG) was first recognized as a potential hazard ingredient in humidifier disinfectants, which caused an outbreak of pulmonary fibrosis in South Korea. However, the underlying mechanisms involved in PHMG-induced pulmonary fibrosis have not yet been fully elucidated. Therefore, this study mainly focuses on the effect of PHMG on surface tension to unveil the influence and involved mechanisms in PHMG-induced pulmonary fibrosis. C57BL/6J mice were exposed to sub-acute PHMG aerosol for 8 weeks. The results indicated that PHMG induced pulmonary fibrosis combined with elevated surface tension. Results from in vitro study further confirmed PHMG elevated surface tension by inhibited pulmonary surfactant. Mechanistically, PHMG suppressed the key surfactant protein SP-B and SP-C by inhibiting protein expression and block their active sites. The present study, for the first time, revealed the molecular mechanism of PHMG-induced pulmonary fibrosis based on pulmonary surfactant inhibition mediated surface tension elevated. And pulmonary surfactant may be a potential target for further intervention to prevent PHMG-induced fibrosis or alleviate the symptom of relevant patients.

We integrated the high-speed synchrotron X-ray phase-contrast imaging (PCI) with a modified Kolsky compression bar loading platform to visualize the dynamic failure processes of cross-ply glass fiber reinforced composites (GFRCs). Four S-2 glass/SC-15 composite specimens were prepared, having similar thicknesses but different stacking sequences, namely as [012/9012], [9012/012], [08/908/08], and [908/08/908]. Three-dimensional synchrotron X-ray computed tomography and scanning electron microscopy (SEM) were employed to examine the microstructures and quantify the fiber volume fractions. Each specimen was notched and subjected to a dynamic three-point flexural loading. The onset of cracking close to the notch tip, crack propagation in 0° or 90° plies and their interface, crack opening, and ultimately failure of the specimen were captured by high-speed synchrotron X-ray PCI. Additional dynamic experiments were performed to determine the average time when the stress wave propagated through the specimen and correlate the X-ray images with the specimen's force-deflection response. Finally, the surface morphology of each specimen after the dynamic loading was imaged by SEM. Comparison between real-time X-ray images and post-fracture SEM images demonstrated the capability of the X-ray method to record damage evolution inside composites. Furthermore, the high spatial and temporal resolutions of the X-ray setup and edge enhancement by PCI enabled the identification of microscale damage features within 1 μs. Two damaging processes were identified, crack growth was quantified, and fracture toughness of the composites was evaluated. The method is deemed useful to reveal microscale damage mechanisms and track cracking behaviors inside cross-ply GFRCs under dynamic loading in real time.

This study aims to isolate interactions between plies and tows and reveal fundamental physics involved in transverse impact on fiber-reinforced composite (FRC) structures. Composite strips were sectioned from large panels and characterized by optical photography, three-dimensional synchrotron X-ray computed tomography, and scanning electron microscopy (SEM). Each strip was impacted perpendicularly by a right circular cylinder (RCC) projectile at a velocity ranging from ~ 150 to 600 m/s. The global strip behavior, as well as localized deformation and failure of the strip near the projectile corner, were both captured by high-speed optical imaging. S-Glass FRC strips were observed to fail in tension ahead of the RCC projectiles’ flat surfaces while Kevlar® FRC strips fractured at the projectile corners. The concept of critical velocity region previously used for impact on yarns was introduced to define different failure modes of each composite strip type. The strip damage extent was found to increase with the impact velocity and reach the maximum at the upper limit of the critical velocity region. Above the critical velocity region, the damage extent decreased with impact velocity. Wave propagations and load histories in the composite strips during impact were quantified and compared with Smith’s theory. Finally, critical velocities of single fibers, yarns, and composite strips and ballistic limits of single-ply and multi-ply composite panels were compared to provide insight into the design of impact-resistant fabrics and composites.

Structural design of nuclear power plant project is an important sub-discipline of civil engineering. Especially after appearance of the fourth generation advanced high temperature gas cooled reactor, structural mechanics in reactor technology becomes a popular subject in structural engineering. As basic ingredients of reflector in reactor, graphite bricks are subjected to high temperature and irradiation and the stress field of graphite structures determines integrity of reflector and makes a great difference to safety of whole structure. In this paper, based on assumptions of elasticity, side reflector is regarded approximately as a straight cylinder structure and primary creep strain is ignored. An analytical study on stress of IG110 graphite parts is present. Meanwhile, a finite element procedure for calculating stresses in the IG110 graphite structure exposed in the high temperature and irradiation is developed. Subsequently, numerical solution of stress in IG110 graphite structure is obtained. Analytical solution agrees well with numerical solution, which indicates that analytical derivation is accurate. Finally, influence of temperature, irradiation dimensional change, creep and Poisson’s ration on stress field, variation of stress against time and deformation of structure are discussed.

The leading and trailing edges of turbine airfoils are highly susceptible to impact by foreign object debris (FOD) entrained in the gas stream of turbine engines. In this study, a narrow specimen geometry is implemented to study the FOD impact behavior of low curvature airfoil edges. Silicon carbide (SiC) ceramic specimens with and without an environmental barrier coating (EBC) are used as target materials. The EBC consists of an air plasma sprayed mullite topcoat (~166 μm) and silicon bond coat (~58 μm). Spherical (⌀ 1.5 mm) FOD simulants of silicon nitride (Si3N4), partially stabilized zirconia (PSZ), and steel are used as impactors. A modified gas gun is used to generate impact damage at normal incidence and velocities ranging between 300 to 400 m/s. In situ phase contrast X-ray radiographs, which render 2D representations of the internal transient damage, are captured during the impact experiments. Impactor hardness and toughness are found to primarily influence damage in the coating. Relative to wide specimens, the narrow specimens experience a greater level of cracking and this is postulated to result from reduced self-confinement. Irrespective of specimen geometry and impactor material type, limited cracking (i.e. enhanced shielding) is observed for the coated condition.

We report the application of high-speed synchrotron X-ray phase contrast imaging (PCI) in real-time damage characterization for glass fiber reinforced composites (GFRCs) subjected to dynamic loading. Dynamic single-edge notched bending (DSENB) experiments on pre-notched S-2 GFRCs were performed on a modified Kolsky compression bar. During loading, the synchrotron X-ray beam penetrated through the composite specimen from the side to detect damage evolution inside the material. Entire dynamic events were recorded by a high-speed camera as image sequences.0° and 90° unidirectional and cross-ply composites were investigated. An optical imaging technique was also employed to capture similar dynamic events in comparison with the radiographic imaging. It is demonstrated that high-speed X-ray PCI had sufficient phase contrast to characterize a crack initiation at a 20-μm spatial resolution within 920 ns and track the crack geometry during propagation, thereby providing reliable data to quantify the dynamic damage resistance of GFRCs. Furthermore, being capable of recognizing microscopic damage-related features at a sub-10-μm resolution, high-speed X-ray PCI provided fundamental material failure mechanisms to reveal the essential of macroscale structural failure of composites. It can also track the damage evolution inside and between individual plies of laminated composites. However, current high-speed X-ray PCI technique only supports in-situ observation and the high timing and spatial resolutions are limited within a field of view of ~2.5 mm in square, preventing its application in the three-dimensional and larger-area damage detection for GFRC structures.

We propose a method to measure multiple dynamic material constitutive parameters of unidirectional fiber reinforced composites (FRCs) in a single experiment. Dynamic short-beam shear (DSBS) experiments were performed on a modified Kolsky compression bar, with integration of high-speed imaging and digital image correlation (DIC). The unidirectional FRCs investigated were S-2 glass fiber reinforced matrix of TGDDM-Jeffamine® D230 with monoamine functionalized partially reacted substructures (mPRS) and commercially available SC-15. Analytical solutions of normal and shear strains of a composite beam were derived based on Timoshenko beam theory, assuming material to be transversely isotropic and have different moduli in tension and compression in each principle material orientation. Tensile and compressive moduli were inversely computed through monitoring normal strain slope when specimen was constantly loaded at a speed of ~7.3 m/s within a small deflection. Non-linear shear stress-strain behavior of the composite was described via Ramberg–Osgood equation. Finite element (FE) analysis was conducted in ABAQUS, simultaneously defining via user subroutine UMAT the transverse isotropy of material, bi-modulus constitutive model, and non-linear shear stress-strain relation. The method proposed in this work was validated by comparing strain distributions computed by FE model and DIC measurements. Comparing with traditional dynamic tensile, compressive, and shear experiments on FRCs, this method significantly simplifies the specimen preparation and design of complicated gripping fixtures for multiple experiments. Furthermore, systematic errors resulting from variations of specimen geometry and dimension, loading direction, and instrumentation are reduced, thereby providing compatible data for numerical studies on impact behavior of composites.

We visualized, in real time, the deformation and failure of single fibers that were transversely cut at high loading rate. A reverse impact experimental technique was employed to introduce the dynamic cutting load onto the fiber. The failure process of the fiber was captured via an ultra-high-speed camera combined with an ultra-long working distance objective lens. Three failure modes were identified: partial penetration followed by tensile failure, complete incision and bending-induced brittle failure without penetration, corresponding to the KevlarⓇ KM2 Plus, DyneemaⓇ SK76 and S-2 Glass fiber, respectively. Such failure modes were found to be rate-independent but highly rely on the fiber nanostructure. It was found that all fibers had an increased energy absorption as the rate increased. Effects of fiber length and cut angle were also studied, potentially providing insight into the material design of cut-resistant textiles or composites.

In this study, the dynamic cracking processes in porcine cortical bone were visualized in real-time using the high-speed synchrotron X-ray phase-contrast imaging (PCI) technique in three osteon orientations: in-plane transverse, out-of-plane transverse and in-plane longitudinal. The dynamic flexural loading applied on the pre-notched bone specimens was introduced by a modified Kolsky compression bar. High-speed X-ray images of the entire loading events were documented with a high-speed camera. Three-dimensional X-ray micro-computed tomography was conducted to examine the intact microstructures and obtain the basic material properties of the bone material used for mechanical characterizations. The onset location, where crack initiated, and the subsequent direction, along which the incipient crack propagated, were measured quantitatively using the high-speed X-ray images and the latter was found dependent on the osteon direction significantly. The crack propagation velocities were dependent on crack extension over the entire crack path significantly for all the three directions while the initial velocity for in-plane longitudinal direction was lower than the other two directions. Straight-through crack paths were observed for in-plane longitudinal specimens while the cracks were deflected and twisted in the in-plane transverse direction. For out-of-plane transverse direction, the cracks follow paths with tortuosity fall in between the other two directions, showing a mixed mode of fractures of the former two extreme cases. The toughening mechanisms, visualized by the high-speed X-ray images, and the corresponding fracture toughness, evaluated in terms of fracture initiation toughness and crack growth resistance curve (R-curve), were also found significantly different among the three osteon directions, suggesting an overall transition from brittle to ductile-like fracture behaviors at the dynamic displacement rate (5.4 m/s) as the osteon orientation varies from in-plane longitudinal to out-of-plane transverse, and to in-plane transverse eventually.

Insight into the detailed fracture processes of single high-performance fibers improves understanding for the nature of their unique resistances to external loads. Here, we show the in-situ observation of entire fracture processes of an uncoated single Kevlar® KM2 Plus and Dyneema® SK76 fiber cut by a razor blade at various angles in a Scanning Electronic Microscope (SEM), including initial contact, deformation, crack initiation and propagation until final failure. The effects of gauge length, sputter coating of the platinum, fiber type and cutting angle on the fiber failure were investigated and discussed. The mass-efficient cutting resistance of a single fiber was evaluated by the specific energy. The diversity of the failure modes and cutting resistance were analyzed and attributed to the specific fiber nanostructure and different cutting angles.