Forces in mechanics最新文献

The present work focuses on the manufacturing, mechanical characterization, and modeling of hybrid Flax/Hemp/Polypropylene (PP) composites under dry conditions. Geometric parameters of the fibers were measured both before and after the melt processing. The results indicated that the processed fibers, especially the hybrid ones, had a narrowed length distribution with an average fiber length of 0.48 mm for hybrids compared to 0.62 mm for non-hybrids. The hybrid composites were mechanically characterized using basic and loading-unloading tensile tests with various fiber combinations and weight percentages. The study also examined the effect of strain rate and cutting angle on the behaviors of the composites. The results demonstrated the significance of fiber orientation as the primary factor in explaining mechanical variations. The tensile strength and Young's Modulus of FH30 composites (PP + 15 wt% flax + 15 wt% hemp) increased by about 24.1 % and 10.9 %, respectively, when the plates were cut into dumbbell shapes at a 90° angle to the injection molding flow direction, compared to a cut at 0° The study also showed that the tensile strength is directly proportional to the mass fraction of reinforcements, with an increase in tensile strength by 7.9 % for 0° cut angle specimens between FH10 (PP + 5 wt% flax + 5 wt% hemp) and FH30 bio-composites, while the uniform strain is inversely proportional to the mass fraction of reinforcements, evidenced by a reduction in uniform strain of 30 % between FH10 and FH30 samples. Morphological observations revealed the presence of bands indicating the propagation of micro-cracks, as well as debonding or cohesive failure. Finally, a Perzyna-type elasto-viscoplastic constitutive model was applied to accurately predict the overall mechanical response of a hybrid composite material. Specifically, the model successfully captured the tension deformation behavior of hybrid natural short-fiber thermoplastic composites, including the elastic stage, yield stress, and nonlinear hardening.

Composite materials are increasingly being used in aircraft components such as fuselage panels which are subject to collision with debris during take-off/landing or in flight. This article provides an analysis of the impact resistance capability of graphene doped T700 (T700G) multilayer composite, when subjected to steel projectile impacts. Test coupons with 300×300 mm were impacted by steel spherical projectiles, with impact energies ranging from 34 J to 338 J, using a compressed air operated cannon. Test data, such as impact and absorbed energy were determined through impact and residual projectile velocity, acquired using ballistic chronograph and two high speed cameras. Damage assessment was performed using non-destructive techniques such as Ultrasonic testing before and after impact test. Through modelling and simulation, using ABAQUS/Explicit, and recording the change of projectile velocity, the energy loss of projectile is calculated, and the impact resistance is judged together with damage extent. T700G has similar impact resistance to AL2024, underperforming when impacted by larger projectiles and presenting an overall higher damaged area.

Kevlar and glass-based fabric-reinforced polymer composites possess excellent impact resistance, corrosion and high specific strength properties which makes them suitable candidature for the fabrication of industrial helmets, riot shields, automobile parts etc. The polymer composite components are prone to impact failure, which restricts their wide commercial usage. In this work, to enhance the impact damage resistance of polymer composite laminates, a hybridized material model consisting of glass and Kevlar fabric was employed. The hybridization of Kevlar ‘K’ with glass ‘G’ fabric [K/K/G/G/K] results in a cost reduction of 32 % without any significant variation in performance when compared to non-hybrid Kevlar fabric-based composite laminate [K/K/K/K/K]. In comparison to plain glass fabric laminates [G/G/G/G/G], the [K/K/G/G/K] configuration exhibits a significant 16.68 % improvement in energy absorption. This improvement is rooted in a parametric study and optimization process employing the Preference Selection Index (PSI) technique to determine the optimum stacking sequence of fabrics within the composite laminate. In addition, it evaluates the projectile limit velocity necessary to prevent failure and assesses the total deformation for an optimized stacked [K/K/G/G/K] composite, taking into account various projectile shapes conforming to low-velocity impact applications. The results of this study provide valuable insights into the properties and capabilities of the hybrid composite laminate and may pave the way for the development of more effective materials for impact protection in various applications.

The use of steel beams with variable sections along their length is getting more attention in recent years. These variable sections can vary gradually along the beam or change abruptly as a drop or a step. The current study investigates the lateral torsional buckling (LTB) of stepped steel beams with flanged I section subjected to uniformly distributed pressure on the top flange. The studied parameters are the step height, the step length, and the boundary conditions of the beam. The finite element method is used to carry out a linear buckling analysis of the beams’ models. The results show significant degradation in beams LTB strength due to the jump of the beam's section. Reducing the simply supported beam depth by 25 % reduces LTB strength by about 40–50 %, while reducing the fixed beam depth by 25 % reduces LTB strength by about 30–40 %. Further reduction in depth showed no significant additional reduction in simply supported beams strength, while the fixed beams showed another 30–40 % reduction in strength with another 25 % reduction in beam total depth. The step made the compressive stress transfer between the two flange parts through the web.

The present study is the continuation of a previously published one (Part I), in which the D- (three-dimensional distance between the sources of any two successive acoustic events) and P-functions (the rate of the energy of the acoustic signals) were introduced for the analysis of the acoustic activity developed in marble specimens under uniaxial tension. The concepts introduced in Part I and the analysis procedure analytically described there, are here employed to analyze the acoustic emissions data gathered from additional experimental protocols in order to support and validate the conclusions drawn in Part I. In this direction, the acoustic activity generated in marble and concrete (either plain or reinforced with short polyolefin fibers) specimens under uniaxial compression or three-point bending, respectively, is studied in the direction of detecting characteristics of the temporal evolution of the D- and P-functions that could provide early hints warning about upcoming fracture. The evolution of the D- and P-functions is considered in juxtaposition to that of the F-function, which is in fact a convenient and flexible mean for the quantification of the average frequency of generation of the acoustic events. The conclusions drawn here are in excellent agreement with the respective ones drawn in Part I, suggesting that the D- and P-functions can indeed be a valuable tool in hands of engineers working in the field of Structural Health Monitoring of structures made of brittle building materials.

The main objective of this study is to investigate the vibration and static analysis of a sandwich composite plate in the hygrothermal environment. The plate consists of three layers such as an Aluminum auxetic core and Graphene platelet-reinforced composite (GPLRC) facing sheets. Based on the Halpin-Tsai theory and Gibson's model, the macro mechanical properties of facing sheets and auxetic core are derived. Via Reddy's third-order shear deformation theory (TSDT), the equations of motion of the sandwich plate are obtained and solved by both Navier and the generalized differential quadrature method (GDQM). The current formulation is validated by comparing the numerical results with those that are reported in the literature. Finally, the influence of different parameters such as the inclined angle of auxetic cells, thickness to the length, and core to total thickness on the natural frequencies, deflection and stresses of the sandwich plate, is examined. Even though some studies have been conducted to investigate the bending or vibration behavior of sandwich structures with negative Poisson's ratio (NPR) cores, the bending and vibration behavior of such structures in the hygrothermal environment is remained unexplored. Additionally, the analysis of stress component variations along the thickness of the plate was a novel feature that has not been addressed in prior studies on the similar structure.

Engineers are tasked with the challenging task of evaluating the performance and analyzing the risk of systems in the context of performance-based seismic design. All sources of random uncertainty must be taken into account during the design phase in order to complete this assignment. The performance limit states for a structure must be defined using appropriate procedures that take into consideration the system characteristics describing the structure, the soil, and the loads applied to the structural reactions. The main objective of this study is to conduct an in-depth analysis, both linear and non-linear (Pushover), of seismic vulnerability for a reinforced concrete (RC) structure. This aims to probabilistically evaluate the effectiveness of composite materials, particularly those reinforced with glass and carbon fibers, in reducing seismic risk when used to reinforce structural columns. The outcomes of this study will provide valuable insights into the efficacy of FRP reinforcements in enhancing seismic resistance, regardless of the analytical approach adopted (linear or non-linear). They reveal a seismic risk reduction of 48 % for structures equipped with glass fiber-reinforced columns and 67 % for those with carbon fiber-reinforced columns.

Offshore renewable energy structures are subject to harsh environments with loading from wind, wave, and tides which introduce fatigue damage in corrosive and erosive environments. An effective approach that has been found to improve mechanical and fatigue resistance of engineering structures is employment of Additive Manufacturing (AM) technology. However, little research has been conducted for implementation of AM technology in offshore renewable energy structures. This study aims to collate and critically discuss the advantages that AM technology can offer to enhance the lifespan of offshore renewable energy structures. In addition to fatigue life improvement, the potential of AM technology to enhance corrosion and erosion resistance in offshore renewable energy structures has been explored. It has been found in this study that among the existing AM techniques, Wire Arc Additive Manufacturing (WAAM) offers promising potentials for life enhancement of offshore wind turbine and tidal turbine support structures. Early research into the potential of using WAAM to create corrosion resistance coatings and components highlights many benefits achieved from this new emerging manufacturing technology, but further research is required to justify the use of the processes for commercial applications. In terms of erosion and wear resistance even less research has been conducted but initial findings show that AM has the potential to add a great level of resistance compared to the wrought material. This study presents the key advantages that AM technology offers to enhance the design life and integrity of offshore renewable energy structures as a first step towards unlocking the great potentials of AM for consideration and implementation in the energy transition roadmap.

Geo-materials naturally display a certain degree of anisotropy due to various effects such as deposition. Besides, they are often two-phase materials with a solid skeleton and voids filled with water, and commonly known as poroelastic materials. In the past, despite numerous studies investigating the vibrations of strip foundations, dynamic impedance functions for multiple strip footings bonded to the surface of a multi-layered transversely isotropic poroelastic half-plane have never been reported in the literature. They are first presented in this paper. All strip foundations are assumed to be rigid, fully permeable, and subjected to three types of time-harmonic loadings. The dynamic interaction problem is investigated by using an exact stiffness matrix method and a discretization technique. The flexibility equations are established by enforcing the appropriate rigid body displacement boundary conditions at each footing-layered soil interface. Numerical results for dynamic impedance functions of two-strip system are presented to illustrate the influence of various effects on dynamic responses of multiple rigid strip foundations.

The current computational investigation employs the stochastic extended finite element approach, which the authors have previously developed, to investigate the probabilistic fracture response of double edge cracked orthotropic laminated composite plates under varying stress conditions. The well-known extended finite element method is used to determine the mean and coefficient of variation of stress intensity factors KI and or KII by treating the input parameters as random variables. This is done under the assumption that all of the laminated plate's layers are perfectly bonded to one another and that there is no delamination effect between the layers, the matrix, or the fibres. And it's believed that the plate has through thickness crack. A combination of input random Gaussian variables is used to model the various input factors, such as the lamination angle, the applied loads, and the crack parameters (such the crack length and location). Typical numerical results are shown to investigate the effects of varying degrees of uncertainty in the lamination angle, crack length, crack length to plate width ratio, crack positions, and applied tensile, shear, and combined (tensile and shear) stresses. An excellent agreement arises when the findings generated with the stochastic extended finite element method methodology are assessed against the results found in the published literature through Monte Carlo simulations.