Equivalent Mechanical Properties Research Articles

Tuned Sloshing Dampers With Large Rectangular Core Penetrations

Abstract Space restrictions at the top of tall buildings may necessitate using tuned sloshing dampers (TSD) tanks with large rectangular penetrations to accommodate the structural core of the tower. A finite element model is employed to predict the natural sloshing frequencies and mode shapes of liquid sloshing in a rectangular tank with a rectangular core. Equivalent mechanical properties are determined to predict the sloshing response. Frequency response predictions of wave heights, sloshing forces, and energy-dissipation per cycle agree with results from shake table testing conducted on a rectangular tank with a rectangular core. Energy dissipation due to flow around the core adds considerable damping to the liquid and is proportional to the response velocity-squared. Nonlinear coupling among sloshing modes results in multiple peaks in the frequency response plots near the fundamental resonant frequency. An interior core with a broad dimension in one direction substantially reduces the fundamental sloshing frequency and equivalent mechanical mass in the perpendicular direction; however, the fundamental sloshing frequency and equivalent mechanical mass in the parallel direction are only influenced marginally. Large rectangular cores reduce the proportion of the total water mass that is effective in controlling tower motion. A TSD with a rectangular penetrating core may enable a TSD option to be considered for the control of a tall building in cases where a traditional rectangular TSD is infeasible.

Dynamic response of auxetic structures

Auxetic materials have been investigated since the 1990’s, they are defined by a negative Poisson’s ratio which gives them interesting capabilities in energy and shock absorption. They are usually lattice structures (2D or 3D array of unit cells), which gives them high stiffness to weight properties and their properties can be tuned to suit a given application. Several papers have been published on new auxetic designs, their static equivalent mechanical properties, shock absorption properties and their manufacturing. Their dynamic behavior has not been studied to date and this is the main purpose of this paper. We will present a novel design that facilitates 3D printing with SLA printers and then examine the dynamic behavior of an auxetic structure between 0 and 1 kHz. In order to explain the unusual behavior of the structure, an initial theoretical model of non-linear spring has been developed with partial success.

An inelastic-damage micromechanical model based on the wing- and secondary-cracking mechanisms under dynamic loading

For most rock materials, there exists a coupling between inelastic deformations caused by crack displacements on micro-crack faces and damage evolution due to nucleation and growth of wing- and secondary-cracks. While rock material is subjected to dynamic loading, the interaction between micro-cracks plays an important role in materials behavior. The self-consistent homogenization scheme is implemented in this paper to consider micro-cracks interaction and determine the equivalent mechanical properties of micro-cracked rock deteriorated by damage evolution. The aim of this article is to develop a self-consistent based micromechanical damage model by taking into account the wing- and secondary-cracking mechanisms accompanied by inelastic strains caused by crack displacements under dynamic compressive loading. While stress intensity factors in tensile and in-plane shear modes at flaw tips exceed the material fracture toughness in modes I and II, respectively, wing- and secondary-cracks are sprouted and damage evolution occurs. For closed cracks, an appropriate criterion for the secondary-crack initiation is proposed in this paper. Moreover, the evolution rule for the secondary-crack is determined based on the principles of dynamic fracture mechanics. The developed model algorithm is programmed in the commercial finite difference software environment for numerical simulation of rock material to investigate the relationship between the macroscopic mechanical behavior and the microstructure. The fracture toughness parameters of the rock samples are experimentally determined. The rock microstructure parameters (average initial length and density of flaws) are studied using scanning electron microscopy. In order to verify the developed model, a series of numerical simulations are carried out to numerically reproduce the Split-Hopkinson pressure bar test results. The numerical simulation results are in agreement with the experimental data. The simulation results demonstrate that the developed micromechanical model can adequately reproduce many features of the rock behavior such as softening in post-peak region, damage induced by wing- and secondary-cracks and irreversible deformations caused by crack displacements on micro-cracks. Furthermore, the softening behavior of rock material in the post-peak region is affected by considering inelasticity and the secondary-cracking mechanisms. Therefore, the rock sample simulation with the coupled inelastic-damage model can increase inelastic deformations in the post-peak region as a result of irreversible strains caused by crack displacements on micro-cracks. The simulation by considering the secondary-crack mechanism leads to an increase in the microcracking process and damage in rock material.

Microstructure and biomechanical characterisation of jujube branches

The mechanical properties of jujube branches are the basis of designing and optimising the working parameters of pruning operations and branch crushing machinery. The mechanical properties of the cell wall of jujube branches were measured using a nanoindentation technique, and the representative volume element for characterising the microstructure of a jujube branch was established using a computed tomography (CT) X-ray technique. In addition, the macro equivalent mechanical properties of jujube branches were predicted using finite element analysis of the representative volume elements. The accuracy of the finite element simulation results was verified through a macro test. The results show that the estimated mechanical properties of jujube branches obtained by using the representative volume element were slightly higher than those obtained by the macroscopic methods but the prediction errors were <5.80%, which verifies the accuracy of the finite element simulation method.

Equivalent mechanical properties of tensegrity truss structures with self-stress included

Due to the complex structure of tensegrity systems it is often hard to understand their behaviour and estimate their mechanical properties. As a result, they are rarely used in real engineering applications. The present paper focuses on the evaluation of equivalent mechanical properties of various tensegrity modules based on a continuum model. The aim of the applied model is to facilitate the identification and understanding of mechanical characteristics of tensegrities through their comparison with a continuum body with equivalent features. The model is built by assuming that the strain energy of an unsupported tensegrity module or structure is equivalent to the strain energy of a solid. The approach enables to estimate the influence of self-stress on deformation of the structure, identify the influence of cables and struts on the properties of the whole system, determine equivalent mechanical characteristics, such as Young's moduli, shear moduli, Poisson's ratios etc., and conditions that limit their values. What is more, a qualitative as well as quantitative evaluation and comparison of mechanical properties for various tensegrity modules and systems is possible with the use of the applied technique. A comprehensive analysis of typical tensegrity modules with various elastic symmetries is presented. Using the adopted model, mechanical characteristics are determined and graphs of identified mechanical coefficients for five typical tensegrity modules are presented in relation to the self-stress multiplier and cable to strut properties ratio. The analysis can be useful for the development of extreme mechanical properties of smart tensegrity-inspired 2D or 3D lattices or metamaterials.

Equivalent models and mechanical properties of bio-inspired corrugated sandwich structures subjected to bending loads

Corrugated sandwich structures have been widely used in aerospace and aviation fields due to their excellent performances. In this paper, a new bio-inspired corrugated sandwich structure is designed based on the microstructure of cybister elytra. Moreover, the homogenization method is used to simplify models and the equivalent material parameters are derived by analytical formulation and finite element method (FEM). The mechanical properties of bio-inspired corrugated sandwich structures fabricated by selective laser melting (SLM) and equivalent models are also investigated subjected to bending loads by FEM and experiments. The results show that the bio-inspired corrugated sandwich structure can be equivalent to the orthotropic model better. Increasing the core height, thickness of the core and panel will improve the bending stiffness obviously. The simulation results are consistent with analytical formulation. But the experimental results are little greater due to the dimension deviation between the fabrication and design. Moreover, the equivalent calculation has a much higher accuracy with a relative deviation less than 10%.

Adaptive isolation system combining low-friction sliding pendulum bearings and SMA-based gap dampers

The flag-shaped hysteretic behavior of Shape Memory Alloys (SMAs) can be conveniently used for developing efficient isolation systems, providing energy dissipation without implying residual displacements. This work presents a base isolation layout that combines low-friction curved surface sliders (CSSs) with SMA gap dampers (SMAGDs). The proposed SMAGDs are formed by a group of SMA wires placed in parallel with the CSS isolation system and connected to it through a sliding pin and a slotted ring in order to accomplish the “gap damper” feature. Based on this installation configuration, SMAGDs introduce additional stiffening and energy dissipation to the isolation system only when the displacement of the CSS exceeds a certain threshold or gap displacement dgap, while not being engaged for lower displacements. Consequently, the system exhibits a phased behavior, meaning that its reaction force depends on the amplitude of the displacement. This is particularly convenient for limiting seismic displacements while avoiding at the same time undesirable effects such as high structural accelerations and poor re-centering capability exhibited by alternative systems at low-intensity excitations, e.g. systems based on high-friction CSSs or combinations of CSSs with traditional supplemental energy dissipation devices. The paper describes a preliminary design procedure and the evaluation of the seismic performance of the proposed CSS + SMGAGD system. A leading design parameter of the SMAGDs is the overall cross-sectional area of the SMA wires, which is designed here through a direct displacement based procedure, by introducing some reasonable assumptions for the definition of the linear equivalent mechanical properties of CSS, SMAGD and combined CSS + SMAGD system. This performance-oriented design procedure is aimed at achieving a target displacement demand of the combined CSS + SMAGD system under the maximum credible design earthquake. A parametric study comprising a variety of CSS and SMAGD properties reveals that the proposed isolation layout is suitable to limit the maximum displacement under ultimate limit state earthquakes, providing at the same time satisfactory energy dissipation along with high re-centering capability, and outperforms both low-friction CSSs and high-friction CSSs.

An Investigation of the Bisymmetric Hydrostatic Collapse of Flexible Pipes Based on Equivalent Layer Approaches

AbstractThe hydrostatic collapse strength of a flexible pipe is largely dependent on the ability of its carcass and/or pressure armor to resist radial loading and, therefore, its prediction involves an adequate modeling of these layers. Hence, initially, this work proposes a set of equations to estimate equivalent mechanical properties for these layers, which allows their modeling as equivalent orthotropic cylinders. Particularly, equations to predict the equivalent ring bend stiffness are obtained by simulating several two-point static ring tests with a three-dimensional finite element (FE) model based on beam elements and using these results to form datasets that are analyzed with a symbolic regression (SR) tool. The results of these analyses are the closed-form equations that best fit the provided datasets. After that, these equations are used in conjunction with a three-dimensional shell FE model (FEM) and a previously presented analytical model to study the bisymmetric hydrostatic collapse mechanism of flexible pipes. The predictions of these models agreed well with the collapse pressures obtained with numerical models and in experimental tests thus indicating the potential use of this approach in the design of flexible pipes.

Inherent strain homogenization for fast residual deformation simulation of thin-walled lattice support structures built by laser powder bed fusion additive manufacturing

Numerical simulation of residual deformation in metallic components with dense lattice support structures by the laser powder bed fusion (L-PBF) additive manufacturing process has been a significant challenge due to the very high computational expense in performing both finite element meshing and analysis. In this work, the modified inherent strain method is extended to enable efficient residual deformation simulation of l-PBF components with lattice support structures. The asymptotic homogenization method is employed to obtain the equivalent mechanical properties including the anisotropic elastic modulus and inherent strains given the topological configuration and laser scanning strategy of the thin-walled lattice support structures. A key finding is that the in-plane homogenized inherent strain values decrease with increasing volume density, which can be attributed to the directional dependence of inherent strains for the AM-processed material. Based on the homogenized mechanical properties and inherent strains, the thin-walled lattice support structures can be considered to be an effective solid continuum so that the simulation can be accelerated significantly to obtain residual deformation. Good accuracy of the homogenized mechanical property and inherent strains is validated by comparing the simulated residual deformation with experimental deformation measurement of several lattice structured beams of different volume densities. Efficiency of the proposed method is also demonstrated through numerical examples to have 80 % reduction in number of elements and nearly 10x speedup in computing time. In addition, the scalability of the proposed method is also verified through application to a complex L-PBF component fabricated with thin-walled support structures.

Equivalent mechanical properties of X-ray and E-beam cross-linked vitamin E blended ultrahigh molecular weight polyethylene.

The influence of X-ray cross-linking compared with electron beam cross-linking on the mechanical and thermal properties of UHMWPE blended with 0.1 wt% vitamin E was investigated. Two X-ray doses (80 and 100 kGy) and two irradiation temperatures (RT: room temperature; 100 °C: warm) were considered. The reference was Vitelene® a vitamin E stabilized UHMWPE cross-linked with 80 kGy e-beam at 100°C. Uniaxial tensile and small punch testing were conducted. The Izod impact strength and the thermal properties were determined. The yield, ultimate tensile strength and elongation were 21.7 MPa, 48 MPa, and 393% for Vitelene® and 21.7 MPa, 47 MPa, and 402% for X (80 kGy)-warm, respectively. The peak load, ultimate displacement, and work to failure accounted for 63 N, 5.7 mm and 331 mJ for Vitelene® and 65 N, 5.6 mm, and 322 mJ for X (80 kGy)-warm respectively. The Izod impact strength of Vitelene® amounted to 81 kJ/m2 , that of X (80 kGy)-warm to 82 kJ/m2 . Crystallinity of both was 52%. The melt temperature of Vitelene® was 140 °C, that of X (80 kGy)-warm 139°C. In conclusion, using the same irradiation temperature (100 °C) and dose (80 kGy), the different radiation sources e-beam and X-rays resulted in equivalent thermal and mechanical properties.

Determination of the equivalent properties of periodic heterogeneous composite plates using the structural genome approach

A structural genome (SG) is defined as the smallest structural building block of composite materials. In this study, we use the concept of structure genome to propose a simple approach for obtaining the equivalent mechanical properties of periodic heterogeneous composite plates. Firstly, an SG from the structural model of a periodic heterogeneous composite plate is extracted. Secondly, a python script is developed in commercial software ABAQUS to conveniently impose periodic boundary conditions and apply different loads on the SG as well as obtain the equivalent mechanical properties of the structural genome. To verify the proposed SG approach, numerical examples are presented and discussed for both linear and nonlinear elastic cases. The results show that this approach is efficient and the results are of sufficient precision to calculate the mechanical properties of both linear and nonlinear elastic periodic heterogeneous composite plates.

Design of Prepreg Compression Molding for Manufacturing of CFRTP B-pillar Reinforcement with Equivalent Mechanical Properties to Existing Steel Part

Prepreg compression molding (PCM) is a well-known process for manufacturing of carbon fiber reinforced thermo-plastics (CFRTP) products with high quality and production rate. However, the design method used for the development of automotive parts has not been clearly presented. In this paper, we propose a process chain that can satisfy the stiffness of existing steel products. First, the CFRTP product of a B-pillar reinforcement to satisfy the bending deformation of an existing product is designed using a structural analysis and genetic algorithms. Next, forming conditions of the product are determined by a forming analysis. To investigate the feasibility regarding the mass production of the PCM process, a rapid heating and cooling system was applied to PCM molds. The heating and cooling times of the molds were calculated using a computational fluid dynamics analysis. Finally, a CFRTP product was fabricated and its bending deformation, dimensional accuracy, and weight were evaluated.

Ti Alloy Three-Way Pipe Fabricated by the Combination of 3D Printing and Cold Isostatic Pressing

In this study, complex-shaped Ti alloys with near-full density, using three-way pipe as an example, were achieved by the combination of 3D printing and cold isostatic pressing (CIP). A new CIP capsule consisting of porous internal support core and the external shell was prepared by 3D printing, which made it feasible to achieve internal and external co-pressing on Ti-6Al-4V powder during CIP. Therefore, complex-shaped green body was obtained with good surface quality, without obvious defects or cracks. After sintering at 1230 °C, the sintered sample had equivalent mechanical properties (hardness = 382 HV, elongation = 15.5%, tensile strength = 929 MPa and yield strength = 862 MPa) compared to the ASTMB381 standard. This study presents a novel method for fabricating complex-shaped Ti alloys with comprehensive mechanical properties.

Homogenization-based multiscale analysis for equivalent mechanical properties of nonwoven carbon-fiber fabric composites

To improve fuel efficiency in the automotive industry, several researchers have made many attempts to replace heavy materials among the automotive components. Hence, carbon-fiber-reinforced plastic (CFRP) composites have drawn significant interest from the automotive and aerospace industries. Continuous and discontinuous carbon fiber are used as representative reinforcing materials in composite manufacturing. Recently, the use of discontinuous-fiber-reinforced plastics has increased, compared to that of continuous-fiber-reinforced plastics, owing to their cost efficiency, weight reduction, and relatively easy fabrication and handling. For composite materials, it is very important to predict mechanical properties due to their various constituents and manufacturing method. In this study, we performed a numerical analysis using homogenization technique to evaluate the equivalent mechanical properties of composites combining a nonwoven carbon fiber fabric reinforcement and epoxy resin matrix. We then compared these results with the experimental results. To calculate the equivalent mechanical properties of composites, we modeled repeating unit cells (RUCs) for homogenization-based multiscale approach, and performed finite element analysis. At the microscale level, this method was compared with the rule of mixture (ROM) theory, which is a typical homogenization technique. Based on the proven homogenization technique, we modeled RUCs for randomly distributed nonwoven carbon fiber fabric (NW-CFF) composites at the mesoscale level and calculated its equivalent properties. At the macroscale level, at which these properties could be verified, we compared the equivalent mechanical properties calculated with experimental test results, such as those of tensile, shear stiffness and Poisson’s ratio.

Wave propagation response of multi-scale hybrid nanocomposite shell by considering aggregation effect of CNTs

This research presents the agglomeration effect of reinforcements on wave propagation analysis of multi-scale hybrid nanocomposite shell based on first-order shear deformable theory (FSDT) of shell for the first time. The nanocomposite shell is consist of carbon fiber (CF) as macro reinforcement, carbon nanotubes (CNTs) as nanoreinforcement and epoxy as an initial matrix. Eshelby-Mori-Tanaka method and rule of mixture are implemented in order to predict the equivalent mechanical properties of nanocomposite shell. To derive the motion equation of shell, FSDT is applied and governing equations are attained by employing Hamilton's principle. Dispersion solution is calculated by solving eigenvalue problem and also analytical method is utilized to solve the governing equations and finally wave frequency and phase velocity of nanocomposite shell can be achieved. In detail, several illustrations are presented which influence various parameters such as longitudinal and circumferential wave number, the volume fraction of CF, volume fraction of CNTs inside the cluster and so on are investigated.Communicated by Chandrika Prakash Vyasarayani.

Stiffness design of a multilayer arbitrary BCC lattice structure with face sheets

In this paper, a theoretical stiffness design approach for a body-centered cubic (BCC) lattice structure is proposed. Although numerous studies have focused on lattice structures, particularly BCC lattice structure, there are still some issues that must be further investigated. Homogenization method is always followed that the mechanical properties of lattice structure can be achieved by directly solving the unit cell, since the structure is a periodically repeated sequence of a unit cell. However, the equivalent modulus varies a lot with different array configurations from our study, which indicates that the spatial array configuration also has an important influence on the equivalent mechanical properties. In this paper, “large unit cell” assumption is used to characterize the equivalent modulus of the lattice structure considering array configuration effect, and then validated using the finite element method (FEM) and experiment. The results demonstrate that the mechanical properties vary significantly for different array configurations, even those with the same unit cell topology. Furthermore, the proposed method is extended to an arbitrary BCC unit cell to broaden its application for stiffness design of engineering parts. This research provides a guidance for the stiffness design of lightweight lattice structures.

Ex vivo biomechanical comparison of 2.7\u2009mm string-of-pearl plate versus screw/wire/Polymethylmethacrylate composite fixation and 2.7\u2009mm veterinary acetabular plate for repair of simulated canine acetabular fractures

BackgroundAcetabular fractures comprise 12–30% of canine pelvic fractures and require accurate anatomic reduction and rigid stability to ensure proper healing and minimize future osteoarthritis. Many techniques have been used to repair these fractures, with common techniques including veterinary acetabular plates or use of screw/wire/polymethylmethacrylate constructs. String-of-Pearl™ plating systems have also been used clinically but there is a lack of research supporting their use for these fractures. The purpose of this study was to compare fracture reduction accuracy, biomechanical characteristics, and mode of failure between String-of-Pearls™, veterinary acetabular plates, screw/wire/polymethylmethacrylate constructs in a simulated, ex-vivo acetabular fracture model. We hypothesized that the String-of-Pearls™ constructs would have equivalent or greater mechanical properties and reduction compared to the other constructs.ResultsThe mean craniocaudal acetabular diameter before fixation (mean 25.2 mm; range 20 mm – 30.1 mm) was not significantly different from after fixation (mean 23.9 mm; range 20 mm – 28.3 mm) for any fixation method. Comparison of reduction scores between groups revealed no significant differences. No significant differences were noted for cyclical displacement or stiffness. There was significant difference with superior failure load of String-of-Pearls™ compared to screw/wire/polymethylmethacrylate in the 75th percentile of animal weight (P = 0.0021), and superior failure load of String-of-Pearls™ compared to veterinary acetabular plates in the 50th (P = 0.0232) and 75th percentiles (P = 0.0058). Stiffness of the String-of-Pearls™ construct was significantly greater than the veterinary acetabular plate construct (P = 0.0417). For ultimate load, String-of-Pearls™ constructs were significantly greater than screw/wire/polymethylmethacrylate (P = 0.0331) and veterinary acetabular plates (P = 0.0218).ConclusionAlthough the ease of application for the String-of-Pearls™ implant was subjectively better than other implants, no significant differences were found in fracture reduction scores. The String-of-Pearls™ constructs were stiffer than veterinary acetabular plates and exhibited greater failure and ultimate loads compared to veterinary acetabular plates and screw/wire/polymethylmethacrylate fixations. The String-of-Pearls™ implant appears to be a suitable fixation choice for simple canine acetabular fractures.

Mechanical properties and failure modes of hybrid fiber reinforced polymer composites with a novel liquid thermoplastic resin, Elium®

In virtue of recyclability purposes, higher impact and damage tolerance properties, efficient and ease of fabrication, a new liquid Methyl Methacrylate (MMA) thermoplastic resin, Elium® 188, has been recently developed. This new resin can replace (epoxy) thermoset-based resins for the fabrication of laminates at room temperature with equivalent mechanical properties. Plain weave ultra-high molecule weight polyethylene fiber (UHMWPE), carbon fiber, and their hybrid systems are fabricated by Vacuum Assisted Resin Infusion (VARI) method at ambient temperature. ASTM standard tests of tensile, compression, and shear (both intralaminar and interlaminar) are conducted to determine the mechanical properties with the aim of comparing the results with those of thermosets. Fractographic analyses are performed to have a better understanding of the behavior of these new thermoplastic-based laminates. The test results show the mechanical properties of thermoplastic-based laminates are comparable to those thermoset-based but with the aforementioned advantages, leading to wider applications in the industry.

Linkage Groups within Thiol-Ene Photoclickable PEG Hydrogels Control In Vivo Stability.

Thiol-norbornene (thiol-ene) photoclickable poly(ethylene glycol) (PEG) hydrogels are a versatile biomaterial for cell encapsulation, drug delivery, and regenerative medicine. Numerous in vitro studies with these 4-arm ester-linked PEG-norbornene (PEG-4eNB) hydrogels demonstrate robust cytocompatibility and ability to retain long-term integrity with nondegradable crosslinkers. However, when transplanted in vivo into the subcutaneous or intraperitoneal space, these PEG-4eNB hydrogels with nondegradable crosslinkers rapidly degrade within 24 h. This characteristic limits the usefulness of PEG-4eNB hydrogels in biomedical applications. Replacing the ester linkage with an amide linkage (PEG-4aNB) mitigates this rapid in vivo degradation, and the PEG-4aNB hydrogels maintain long-term in vivo stability for months. Furthermore, when compared to PEG-4eNB, the PEG-4aNB hydrogels demonstrate equivalent mechanical properties, crosslinking kinetics, and high cytocompatibility with rat islets and human mesenchymal stem cells. Thus, the PEG-4aNB hydrogels may be a suitable replacement platform without necessitating critical design changes or sacrificing key properties relevant to the well-established PEG-4eNB hydrogels.

Design-properties relationships of polyurethanes elastomers depending on different chain extenders structures

In this study, the effect of the structure and amount of the chain extenders on the morphological image and physico-chemical properties of some new polyurethane elastomers has been investigated. To achieve this, three series of polyurethane elastomers based on poly(tetramethylene ether) glycol, hexamethylene diisocyanate and chain extenders with different structures (triethylene glycol, 3,6-dithia-1,8-octanediol, 1,6-hexanediol) were synthesized. The chain-extenders which introduce oxygen or sulfur atoms into the polyurethane backbone chains (hard domains) change the behavior of the properties compared to the corresponding polyurethanes chain-extended with aliphatic diols. The structures of the new polyurethane elastomers were examined by FTIR, X-ray diffraction analysis and by atomic force microscopy (AFM). They were also characterized for thermal and tensile properties. The polyurethanes with sulfur into their hard segment structure were found to exhibit improved thermal stability properties and equivalent mechanical properties with polyurethanes obtained with aliphatic diols. This is due to the extensive and many fold hydrogen bond network that characterizes polyurethanes with sulfur in their hard segment structure.