2.5D woven composite has great application prospect in high bypass ratio commercial turbofan engine fan blades due to its comprehensive advantages in mechanical properties and complex component ...forming. For the aero-engine fan blades, vibration fatigue is a working condition that can not be ignored. At present, the research on vibration fatigue behavior of 2.5D woven composite is limited, and there is a lack of numerical model for vibration fatigue behavior simulation. In this paper, a multi-scale model for the first-order flexural vibration fatigue behavior of a 2.5D woven composite cantilever beam simulating the root of engine blade was established. Adopting the fatigue loading simulation method which adopted the fixed cycle jumping strategy, and the damage initiation criterion and fatigue stiffness degradation model based on the leading fatigue failure mechanism, the vibration fatigue test processes of the wrap and weft specimens were simulated respectively. With the established multi-scale model, the stre
The 2.5D woven composite material has good resistance to delamination and impact load. However, its fatigue behavior is lack of investigation. In this work, first-order bending vibration fatigue ...tests were conducted on cantilever beam specimens made of 2.5D woven composites under different nominal stress levels. Test results showed that rapid damage evolution and accumulation occurred in the woven composites under a high stress level. However, under a low stress level, crack growth showed arrest behavior. The square root of residual stiffness showed a linear relation with resonance frequency, so the normalized full-time domain curves can be used to characterize the residual stiffness. On that basis, a residual stiffness model for the studied vibration fatigue specimens under other stress levels was proposed. Besides, a formula of ɛ-N curve was established for guiding the design and analysis of the 2.5D woven composite. To further reveal the failure mechanism, a multi-scale model of the woven composite was proposed. Numerical results showed that the high interlaminar shear stress between the yarn and the matrix near the compressed surface of the specimen caused material damage. This was consistent with the observed fracture topography, which verified the applicability of the multi-scale model.
Full text
Available for:
GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
Short beam shear (SBS) test combined with digital image correlation (DIC) can quickly identify the multiple mechanical properties of unidirectional fiber reinforced resin matrix composites. In ...addition, the complete interlaminar shear stress-strain behavior and interlaminar shear strength of composite materials under uniaxial stress state can be obtained, which is very important to establish the strength criterion of three-dimensional stress state of composite materials with thick section. In order to study the influence of experimental design on the identification accuracy of interlaminar shear mechanical parameters of materials, two stereo digital image correlation systems composed of four CCD cameras were developed for the first time in this paper, and the strain distribution in the front and back surface gage regions of the sample during loading in SBS test was measured. The experimental results show that the shear strain distribution on the front and back surfaces of the sample is asymmetrical, and the r
Buoyant materials, as an important counterweight material of the deep-sea devices, play an important role in providing the equipment with enough buoyance as much as possible. Solid buoyant materials ...(SBMs) have received extensively attention in deep-water surveying and development and petroleum exploration fields in recent years due to their low density, high strength and low water absorption characteristics.In this paper, the classification and the application of SBMs and their recent developments both at home and broad were firstly discussed. Typically, the SBMs can be mainly divided into the chemical and the composite syntactic foams according to their chemical composition and the composite syntactic foam was especially elaborated in this study. Secondly, four basic types of the composite syntactic foams, namely metal-, polymer-, and ceramic- matrix and other types of the syntactic foams, based on their chemical composition of the matrix and the reinforcement. The influence factors such as the essential co
The tensile and compressive properties of the open-hole laminates fabricated with glass fiber reinforced polymer (GFRP) under various temperature/humidity coupled conditions are important design ...parameters for GFRP structures in helicopter. In current work, a comprehensive experimental study about the effects of temperature and hygrothermal on the open-hole mechanical property of HS6/AC318 glass/epoxy multidirectional laminates was conducted. The load-displacement responses, fracture morphologies and failure mechanisms of quasi-isotropic GFRP laminates with a center hole under tensile and compressive loads at the five environmental conditions were compared, and the effects of the temperature and hygrothermal on the open-hole tensile (OHL) strengths and open-hole compressive (OHC) strengths of GFRP laminates were investigated. In addition, the relevancies between the OHL and OHC strength of open-hole laminates and the basic material properties of unidirectional laminates were explored, and some links between the OHL strength and interlaminar fracture toughness were found. The results showed that the OHC strength of open-hole laminates was directly proportional to the 0° compressive strength of unidirectional laminates. Based on the experimental data and analysis an empirical formula of the OHC strength at arbitrary temperature and humidity combined conditions was proposed.
Display omitted
•A comprehensive experimental study is carried out for OHT/OHC properties of HS6/AC318 under five environmental conditions.•An empirical formula of the OHC strength under arbitrary temperature and humidity combined conditions is proposed.•Anomalous high value of FOHTu at ETD is attributed to matrix softening and increased GIc_prop at high temperatures.
Full text
Available for:
GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
To improve the pedestrian outflow in panic situations by suitably placing an obstacle in front of the exit, it is vital to understand the physical mechanism behind the evacuation efficiency ...enhancement. In this paper, a robust differential evolution is firstly employed to optimize the geometrical parameters of different shaped obstacles in order to achieve an optimal evacuation efficiency. Moreover, it is found that all the geometrical parameters of obstacles could markedly influence the evacuation efficiency of pedestrians, and the best way for achieving an optimal pedestrian outflow is to slightly shift the obstacle from the center of the exit which is consistent with findings of extant literature. Most importantly, by analyzing the profiles of density, velocity and specific flow, as well as the spatial distribution of crowd pressure, we have proven that placing an obstacle in panic situations does not reduce or absorb the pressure in the region of exit, on the contrary, promotes the pressure to a much higher level, hence the physical mechanism behind the evacuation efficiency enhancement is not a pressure decrease in the region of exit, but a significant reduction of high density region by effective separation in space which finally causes the increasing of escape speed and evacuation outflow. Finally, it is clearly demonstrated that the panel-like obstacle is considerably more robust and stable than the pillar-like obstacle to guarantee the enhancement of evacuation efficiency under different initial pedestrian distributions, different initial crowd densities as well as different desired velocities.
•Differential evolution is used to optimize the geometrical parameters of obstacles.•Profiles of density, velocity, specific flow as well as crowd pressure are analyzed.•Placing an obstacle in panic situations promotes the pressure to a much higher level.•Physical mechanism of efficiency enhancement is a reduction of high density region.•Panel is more robust than pillar to guarantee the enhancement of pedestrian outflow.
Full text
Available for:
GEOZS, IJS, IMTLJ, KILJ, KISLJ, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK, ZRSKP
Transverse tensile strength of unidirectional (UD) composites plays a key role in overall failure of fiber-reinforced composites. To predict this strength by micromechanics, calculation of actual ...stress in constituent matrix is essentially required. However, traditional micromechanics models can only give the volume-averaged homogenized stress rather than an actual one for a matrix, which in practice will cause large errors. In this paper, considering the effect of stress concentration on a matrix, a novel micromechanics method was proposed to give an accurate calculation of the actual stress in the matrix for UD composite under transverse tension. A stress concentration factor for a matrix in transverse tensile direction is defined, using line-averaged pointwise stress (obtained from concentric cylinder assemblage model) divided by the homogenized quantity (obtained from a bridging model). The actual stress in matrix is then determined using applied external stress multiplied by the factor. Experimental validation on six UD carbon fiber-reinforced polymer (CFRP) specimens indicates that the predicted transverse tensile strength by the proposed method presents a minor deviation with an averaged relative error of 5.45% and thus is reasonable, contrary to the traditional method with an averaged relative error of 207.27%. Furthermore, the morphology of fracture section of the specimens was studied by scanning electron microscopy (SEM). It was observed that different scaled cracks appeared within the matrix, indicating that failure of a UD composite under transverse tension is mainly governed by matrix failure. Based on the proposed approach, the transverse tensile strength of a UD composite can be accurately predicted.
Full text
Available for:
IZUM, KILJ, NUK, PILJ, PNG, SAZU, UL, UM, UPUK
SUMOylation is a reversible post-translational modification that regulates protein function through covalent attachment of small ubiquitin-like modifier (SUMO) proteins. The process of SUMOylating ...proteins involves an enzymatic cascade, the first step of which entails the activation of a SUMO protein through an ATP-dependent process catalyzed by SUMO-activating enzyme (SAE). Here, we describe the identification of TAK-981, a mechanism-based inhibitor of SAE which forms a SUMO–TAK-981 adduct as the inhibitory species within the enzyme catalytic site. Optimization of selectivity against related enzymes as well as enhancement of mean residence time of the adduct were critical to the identification of compounds with potent cellular pathway inhibition and ultimately a prolonged pharmacodynamic effect and efficacy in preclinical tumor models, culminating in the identification of the clinical molecule TAK-981.
PDF
