Quasi-static Mechanical Analysis Research Articles

Comparison of different methods for dynamic characterization of porous-elastic materials

Acoustical simulation of porous-elastic materials requires several properties to be characterized, one of them is the dynamic mechanical behavior of the structure. For this goal, quasi-static mechanical analysis (QMA) is the generally used method executed in the ca. 20-60 Hz frequency range, resulting constant (averaged) mechanical properties. Polymer-based materials, however, are well-known from their time- and frequency-dependent behavior. This implies the need for having frequency-dependent data in a wider frequency range, but the error induced by the fluid motion inside the pores increases with frequency. For that reason, dynamic mechanical analysis (DMA) together with frequency-temperature superposition method was chosen to analyze the possibility of extending the evaluable frequency range. Different measurement setups and strategies were tested and evaluated to minimize the errors coming from machine resonances and other influencing factors, and results were compared to those obtained from the classical QMA measurements. It was finally proven, that with thoroughly chosen technique, DMA can give high quality results for porous-elastic materials as well, in a remarkably wide frequency range.

Aging damage mechanism and mechanical properties degradation of 3D orthogonal woven thermoset composites subjected to cyclic hygrothermal environment

3D orthogonal woven thermoset composites (3DOWCs) can be applied to fabricate the bearing structures of supersonic aircrafts due to their excellent mechanical properties. However, 3DOWCs would be subjected to the cyclic hygrothermal aging caused by the specific service environment of supersonic aircrafts. This paper aims to reveal the cyclic hygrothermal aging mechanism and the consequent degradations of mechanical properties of 3DOWCs. Accelerated hygrothermal cyclical ageing tests were carried out in a simulated service environment of supersonic aircrafts. The aging damage mechanisms were investigated with moisture content monitoring, micromorphology observation and Fourier transform infrared (FTIR) analysis. The evolution of mechanical properties was evaluated by quasi-static mechanical tests (tension, compression and interlaminar shear) and Dynamic mechanical analysis (DMA). The results show that the mechanical properties of 3DOWCs deteriorate significantly with the increasing of hygrothermal aging cycle. Interface debonding, crack propagation, and embrittlement of fiber bundles are the main reasons of the degradation.

Explanation on the Abnormal Behavior during the Nanoindentation Holding Stages by Amplifying Oscillation

Recently, the holding states of nanoindentation experiments have been widely used to analyze the time-dependent deformations of various rocks, and the dynamic mechanical analysis (DMA) method seems to be more applicable than the quasi-static mechanical analysis (QMA) method when the influence of creep deformation on mechanical properties of rocks was analyzed. However, the former method causes an abnormal behavior during the creep holding stages that was not clearly interpreted.2 Consequently, in this study, by amplifying the oscillation of the DMA method, the mechanical mechanism of this phenomenon was explained. Experimental results confirm that the rheological deformation of rocks consists of the creep deformation (depth increasing) and the elastic aftereffect deformation (depth decreasing) during the creep time with small oscillation; once the elastic aftereffect deformation exceeds the creep deformation, the abnormal behavior can be observed. Besides, some other abnormal behaviors might be found for other rock materials when the DMA method with different oscillations is used, which illustrates the complexity and limitation of applying this method. Thus, the QMA method was recommended to investigate the above questions in future studies.

Application of Linear Viscoelastic Continuum Damage Theory to the Low and High Strain Rate Response of Thermoplastic Polyurethane

BackgroundUnderstanding the mechanical response of elastomers to applied deformation at different strain rates and temperatures is crucial in industrial design and manufacture; however, this response is often difficult to measure, especially at high strain rates (e.g. > 100 s− 1), and more predictive methods to obtain constitutive relationships are required.ObjectiveThe objective of the research described in this paper is to develop such methods.MethodThe paper outlines a novel approach combining quasi-static monotonic tests in tension and compression, quasi-static cyclic tests in tension, and high strain rate tests in compression, with dynamic mechanical analysis and time-temperature superposition. A generalized viscoelastic model incorporating continuum damage is calibrated.ResultsThe results show that a model calibrated using data from quasi-static compression and dynamic mechanical analysis can be used to adequately predict the compressive high strain rate response: hence, this paper provides an important step in the development of a methodology that avoids the requirement to obtain constitutive data from high strain rate experiments. In addition, data from FE models of the dynamic mechanical analysis experiments are provided, along with a discussion of data obtained from tensile and cyclic loading.ConclusionsThe paper demonstrates the effectiveness of ‘indirect’ predictive methods to obtain information about high rate behaviour of low modulus materials.

A mechanical-diffusive peridynamics coupling model for meso-scale simulation of chloride penetration in concrete under loadings

A coupled mechanical-diffusive peridynamics (PD) model is developed to simulate chloride penetration in saturated concrete under various loadings at meso-scale. PD is implemented in the architecture of finite element method (FEM) and truss elements are used to substitute for the PD bonds. In the coupled model, damage evolution and crack growth in concrete under loadings and chloride penetration into concrete with updated diffusivity caused by cracks can be investigated simultaneously. At each coupling step, the quasi-static mechanical analysis is conducted by solving the equilibrium equations, while the forward differencing method is adopted for chloride diffusion. Several numerical examples are carried out to validate the proposed PD models in terms of addressing mechanical-diffusive problems. The numerical results coincide with the test findings and clearly indicate that the width and depth of cracks can influence the chloride diffusivity when “threshold crack width” is reached. Additionally, the chloride diffusivity increases with the increase of stress level under high compressive, tensile and flexural stress levels.

A new dynamic balancing method of spindle based on the identification energy transfer coefficient

A new vector matching balance method (VMBM) based on the identification of energy transfer coefficient of spindle rotor system (ETCSRS) is proposed in this paper. This method only needs to extract the original vibration signal of the spindle to compute the spindle rotor system unbalanced vector, and the calculation accuracy depends on the identification precision of ETCSRS. The initial parameters of bearings were calculated by applying Newton-Raphson algorithm based on the quasi-static mechanics analysis of rolling bearings. Through establishing the FEA model of spindle, the structural parameters of the rotor shaft system are obtained and modified by modal correction method. First, the principle of VMBM is verified on a Bentley rotor test bench at different rotating speeds. Second, the verification experiment of VMBM on a high-speed spindle is carried out. Furthermore, the VMBM has a better performance than the influence coefficient method (ICM). The method proposed in this paper is very suitable for on-line dynamic balancing, since it greatly improves the balance efficiency.

A coupling extended multiscale finite element and peridynamic method for modeling of crack propagation in solids

A coupling extended multiscale finite element and peridynamic method is developed for the quasi-static mechanical analysis of large-scale structures with crack propagation. Firstly, a novel incremental peridynamic (PD) formulation based on the ordinary state-based PD model is derived utilizing the Taylor expansion technique. To combine the high computational efficiency of the EMsFEM and advantages of dealing with discontinuous problems of the PD, a coupling strategy based on the numerical base function is proposed, in which the displacement constraint relationships between the coarse element nodes of the EMsFEM and the material points of the PD among the coupling domain are constructed by the numerical base functions and are represented by a coupling strain energy function using the Lagrange multiplier method. Then, a bilinear softening material model is adopted to describe the damage and failure of the bond, and the incremental-iterative algorithms are applied to obtain the steady-state solutions. Finally, several representative numerical examples are presented, and the results demonstrate the accuracy and efficiency of the proposed coupling method for the quasi-static mechanical analysis of large-scale structures with crack propagation. Comparing with the single EMsFEM and PD method, the present coupling method can reduce much computational cost and well deal with crack problems, simultaneously.

Experimental and simulation study on the thermal characteristics of the high-speed spindle system

High-speed spindles often suffer from degeneration in its machining accuracy caused by the uneven distribution of temperature field. In order to improve the machining accuracy of high-speed spindles, a three-dimensional (3D) finite element analysis (FEA) model, which considered the combined effect of thermal contact resistance (TCR) and the change in heat power and stiffness caused by thermal displacements of bearing components on the accuracy of simulation results, was proposed to conduct transient thermal-structure analysis of high-speed spindles. The predictive model for TCR was proposed based on the fractal theory to characterize the rough surface morphology with disorder, self-affinity and non-stationary random features. And a contact mechanics model was developed to consider the influence of asperities’ deformation on TCR. The thermal-structure model of bearing was proposed to calculate the heat power and stiffness based on the quasi-static mechanics analysis. The FEA model proposed in this paper was used to simulate the temperature field distribution and thermal deformations of the high-speed spindle system. Then thermal characteristic experiments were conducted to validate the effectiveness of this model. The results showed that the FEA model was much more accurate than the traditional model which ignored the above two important factors. The temperature field and thermal errors of the spindle system were analyzed.

Finite element modeling and validation of thermomechanical behavior of Ti-6Al-4V in directed energy deposition additive manufacturing

Thermally induced residual stresses and residual distortions in the additive manufactured (AM) parts are two of the major obstacles that are preventing AM technology from gaining wide adoption. In this work, a three-dimensional thermo-elastic-plastic model is proposed to predict the thermomechanical behavior in the laser engineered net shaping (LENS) process of Ti-6Al-4V using Finite Element Method (FEM). It is shown that the computed thermal history and mechanical deformations are in good agreement with the experimental measurements. The main contributions of this study are: (I) in the past, a point-wise comparison between simulation results and experimental measurements is more favored to validate the employed model, where the general picture is lost; rather, to validate the proposed model, the simulated distortion of the bottom surface of a thin substrate is compared with experimental measurements using a 3D laser scanner, in terms of both magnitude and distribution map. (II) Rather few works have been done to show the effectiveness of widely employed quasi-static mechanical analysis in the transient LENS process; as such, both quasi-static and dynamic simulations are performed and compared mechanically to demonstrate the validity of using quasi-static modeling to save computational cost.

Simulation and experimental study on the thermally induced deformations of high-speed spindle system

In order to avoid the degeneration of high-speed spindle's machining accuracy in actual machining caused by the uneven distribution of temperature field at the design stage, a three-dimensional (3D) finite element analysis (FEA) model, which considered the combined influence of thermal contact resistance (TCR) and bearing stiffness on the accuracy of simulation results, was proposed to conduct transient thermal-structure interactive analysis of motorized spindles. And the method to calculate the boundary conditions used in the FEM model were discussed in detail, such as the heat loads, convective heat transfer, TCR and bearing stiffness. Based on the quasi-static mechanics analysis of rolling bearing, the transfer relationships among multiple variables in the equilibrium equation set of bearings were analyzed. Newton–Raphson algorithm, which regarded the contact angle as the iteration variable, was proposed to calculate the heat power and stiffness of bearings and improve the convergence of the algorithm, and the termination criteria of contact angle's searching trial calculation was proposed to improve the accuracy of the algorithm. The Weierstrass–Mandelbrot (W–M) function in fractal geometry was used to characterize the rough surface morphology of bearing rings. The fractal parameters were identified by the power spectrum method, and a contact deformation model of asperities was developed to calculate the contact parameters used in the TCR modeling. Then, the predictive model for TCR, which considered the combined effect of the morphology of bearing rings and the contact deformation of asperities, was proposed. Thermal equilibrium experiments were conducted to demonstrate the validity of the model. The results showed that the FEA model can accurately simulate the temperature field and thermal deformation of the spindle system and that the FEA model was much more accurate than the traditional thermal model of the high-speed spindle system which ignored TCR and bearing stiffness.

An improved peridynamic approach for quasi-static elastic deformation and brittle fracture analysis

An extended bond-based peridynamic (PD) approach is presented for quasi-static mechanical behavior and brittle failure analysis of materials and structures. A local artificial damping is introduced into the peridynamic equations of motion, and a step-by-step loading method and a non-equilibrium criterion are employed to calculate the elastic response quantitatively, simulate the crack initiation and propagation and predict the extreme failure load of structures. The effect of the magnitude of the local damping on the accuracy and efficiency of elastic calculation is investigated. In the proposed model, another important feature lies in the micromodulus of the pair-wise bond, which is described as a continuous function of the distance between two particles within the material horizon and is demonstrated to be more accurate when compared to the earlier PD models using a fixed stiffness constant to describe the interaction of particles. The qualitative and quantitative validity of the approach is established through simulating the mechanical response and fracture of a cantilever concrete beam, including the whole process from the earlier elastic deformation stage to crack initiation and propagation, and making comparisons to the analytical and other numerical data. To further demonstrate the capabilities of the proposed model, the crack propagation and fracture mechanism of a cantilever concrete beam with pre-existing notch is studied, and the effect of the notch location on the extreme failure load and fracture mode of the structure is examined.

Thermal characteristics analysis and experimental study on the high-speed spindle system

In order to avoid the sudden failure of high-speed spindles in the actual machining process caused by an excessive temperature rise at the design stage, a three-dimensional (3D) finite element analysis (FEA) model was proposed to conduct transient thermal-structure interactive analysis of a high-speed spindle. The FEA model considered thermal contact resistance (TCR) at solid joints and bearing stiffness to improve the accuracy of traditional thermal models which ignored TCR. However, TCRs at solid joints and bearing stiffness were often ignored in traditional thermal models of high-speed spindles. This caused inaccuracies in traditional thermal models. The heat generation of the built-in motor was calculated based on the efficiency analysis method proposed by Bossmanns and Tu [1]. Based on the quasi-static mechanics analysis of rolling bearing, the heat generation and stiffness of bearings were calculated by applying the Newton-Raphson algorithm to improve the convergence. The Weierstrass-Mandelbrot (W-M) function, a function of fractal parameters, was used to characterize the rough surface morphology of bearing rings. The fractal parameters were identified by the structure function method and the measurement data of bearing ring’s surface morphology, and a contact mechanics model was developed to calculate the contact parameters used in the model of TCR. Then, a new predictive model for TCR was proposed based on M-T model. The above boundary conditions were applied to the FEA model, and thermal equilibrium experiments were conducted to validate the effectiveness of the model. The results showed that the FEA model was much more accurate than the traditional model which ignored TCRs at solid joints and bearing stiffness.

Creep behavior of composite interlayer and its influence on impact sound of floating floor

Creep-induced changes in dynamic stiffness of resilient interlayer used for floating floor is an important parameter of vibration isolator in long-term use. Compressive creep behavior of a composite layer made from closed-cell foam and fibrous material is investigated using a Findley equation-based method recommended by International Organization for Standardization (ISO). Quasi-static mechanical analysis is used to evaluate the dynamic stiffness influenced by the creep-deformation of the composite layer. It is shown in the present work that the long-term creep strain of the interlayer under nominal load of the floor and furniture is within the zone where dynamic stiffness increases. The changes in low frequency impact sound by the long-term creep deformation are estimated through real scale laboratory experiments and numerical vibro-acoustic analysis.

Modelling the pultrusion process of an industrial L-shaped composite profile

A numerical process simulation tool is developed for the pultrusion of an industrial L-shaped profile. The composite contains the combination of uni-directional (UD) roving and continuous filament mat (CFM) layers impregnated by a polyester resin system specifically prepared for the process. The chemo-rheology and elastic behavior of the resin are obtained by applying a differential scanning calorimetry (DSC) and a dynamic mechanical analyser (DMA), respectively. The process induced stresses and shape distortions are predicted in a 2D quasi-static mechanical analysis. The numerical process model predicts the residual spring-in angle which is found to be close to the one measured from the real pultruded L-shaped products. The residual spring-in angle is further analyzed using the developed simulation tool for different pulling rates. Through-thickness stress variations are found to prevail inside the part such that the UD and CFM layers have different stress levels at the end of the process. The predicted stress pattern is verified by performing a stress calculation using the classical laminate theory (CLT).

Pultrusion of a vertical axis wind turbine blade part-II: combining the manufacturing process simulation with a subsequent loading scenario

This paper in particular deals with the integrated modeling of a pultruded NACA0018 blade profile being a part of EU funded DeepWind project. The manufacturing aspects of the pultrusion process are associated with the preliminary subsequent service loading scenario. A 3D thermo-chemical analysis of the pultrusion process is sequentially coupled with a 2D quasi-static mechanical analysis in which the process induced residual stresses and distortions are predicted using the generalized plane stain elements in a commercial finite element software ABAQUS. The temperature- and cure-dependent resin modulus is implemented by employing the cure hardening instantaneous linear elastic (CHILE) model in the process simulation. The subsequent bent-in place simulation of the pultruded blade profile is performed taking the residual stresses into account. The integrated numerical simulation tool predicts the internal stress levels of the profile at the end of the bending analysis. It is found that the process induced residual stresses have the potential to influence the internal stresses arise in the structural analysis.

Investigation of the Spring-In of a Pultruded L-Shaped Profile for Various Processing Conditions and Thicknesses

In this study, a thermo-mechanical finite element model is developed to predict the spring-in of an industrially pultruded L-shaped profile made of glass/polyester composite. The resin curing kinetics are obtained from the differential scanning calorimetry (DSC) experiments. The development of the resin modulus is derived using the dynamic mechanical analysis (DMA) tests and the effective mechanical properties of the processing composite are calculated using a micromechanical model. The temperature and degree of cure distributions are obtained in a three dimensional (3D) thermo-chemical anlaysis using the finite element method (FEM). The process induced distortions are then calculated using these distributions in a 2D quasi-static mechanical analysis in which generalized plane strain elements are utilized. The predicted spring-in pattern at the end of the process is found to agree quite well with the one observed for the real pultruded parts in a commercial pultrusion company. In addition, the effects of the pulling speed and the part thickness on the spring-in formations are investigated using the proposed numerical simulation tool. It is found that the magnitude of the spring-in increases with an increase in the pulling speed and part thickness.

A study of an embeddable and locatable spinning system via quasi-static mechanical analysis

In this study, a quasi-static model is built to theoretically analyze the distribution of twists and spinning tension in embeddable and locatable spun (ELS) yarn formation zone. Important equations are also derived to determine inner mechanics and external configurations of the ELS yarn formation zones 1, 2 and 3. Analysis results demonstrate that in zones 1 and 2 the tension distribution on the filament and staple strand is directly proportional to their linear mass and square of delivery speed; the larger weight causes a smaller angle between the responding component and the composite strand axis line. The angle between the composite strands 1 and 2 can be simply calculated by dividing the composite yarn velocity by composite strand velocity. Online photographs are provided to validate theoretical analysis of the ELS yarn formation zone configuration and twist distribution in zones 1 and 2.

Measurement of Creep-induced Change of Dynamic Stiffness of Resilient Materials Used for Impact Sound Isolation in Floating Floors

Abstract The creep-induced change of the dynamic stiffness of resilient materials used in vibration isolation systems in floating floors is an important issue, especially with regard to the use of open cell resilient materials, because the change in the dynamic stiffness is a key factor in the performance of vibration isolators, and open cell materials are vulnerable to creep deformation. This study proposes a method for measuring the creep-induced change of the dynamic stiffness that employs quasi-static mechanical analysis under the assumption that the creep-induced change of the mechanical structure of the resilient material is independent of time and stress. The pre-creep dynamic properties of a sample resilient layer measured with a method very similar to the one recommended in ISO 9052–1 are compared with the data measured with the proposed method, and the results illustrate the consistency in the data measured with the two methods. A proposed creep test is performed for a sample resilient layer including open cell material used for a floating floor, and the change in the dynamic stiffness due to creep deformation is assessed by combining the proposed method and the creep test data. The study indicates that the proposed method is able to assess the creep-induced change of the dynamic stiffness and could be useful for the design of vibration isolation systems in long-term use.

Viscoelastic, Mechanical and DOE-Based Study on PP-Nanocomposites

This paper deals with the quasi-static and dynamic mechanical analysis of montmorillonite filled polypropylene composites. Nanocomposites were prepared by blending montmorillonite (nanoclay) varying from 3 to 9% by weight with polypropylene. The dynamic mechanical properties such as storage modulus, loss modulus and mechanical loss factor of PP and nano-composites were investigated by varying temperature and frequencies. Results showed better mechanical and thermomechanical properties at higher concentration of nanoclay. Regression-based models through design of experiments (DOE) were developed to find the storage modulus and compared with theoretical models and DOE-based models.

Evaluation of porous membrane core elasticity and porous morphology for polypyrrole trilayer actuators

Multilayer electroactive polymer actuators consisting of polypyrrole films electropolymerized on a passive polymer membrane core have been harnessed as a source of simple actuation. As an integral component of the actuator, the membrane plays a vital role in the transport of ionic species and largely dictates the stiffness of the layered configuration, yet in past studies the specification of the membrane has remained largely arbitrary. In this investigation, we use quasi-static and dynamic mechanical analysis to investigate the impact of the mechanical properties of the membrane on the actuation response of polypyrrole-based trilayer bending actuators. Candidate materials with distinctly varied microcellular morphologies are identified and include polyvinylidene difluoride, nylon, and nitrocellulose. The quasi-static stress-strain response and the frequency-dependent viscoelastic nature of the candidates are then evaluated. On the basis of mechanical properties these results indicate that polyvinylidene difluoride membranes are superior to the other candidates for application as trilayer actuator cores. Bis(trifluoromethane)sulfonimide doped polypyrrole actuators with polyvinylidene difluoride cores and nylon cores are then fabricated under various synthesis conditions and their electromechanical actuation behavior is reported.