scholarly journals On the use of length scale parameters to assess the static strength of notched 3D-printed PLA

2017 ◽  
Vol 11 (41) ◽  
pp. 252-259 ◽  
Author(s):  
Adnan A. Ahmed ◽  
Luca Susmel
Keyword(s):  
Static Strength ◽  
Length Scale ◽  
Scale Parameters ◽  
3D Printed

A Cyclic Microbend Study on LIGA Ni Microelectromechanical Systems Thin Films

2005 ◽  
Vol 127 (1) ◽  
pp. 16-22 ◽  
Author(s):  
J. Lou ◽  
P. Shrotriya ◽  
W. O. Soboyejo
Keyword(s):  
Thin Films ◽  
Strain Gradient ◽  
Cyclic Deformation ◽  
Microelectromechanical Systems ◽  
Fatigue Behavior ◽  
Cyclic Stress ◽  
Length Scale ◽  
Gradient Plasticity ◽  
Scale Parameters ◽  
Reversed Cyclic

This paper presents the results of recent studies of cyclic microbend experiments and their consequences for plasticity length-scale phenomena in LIGA Ni microelectromechanical systems (MEMS) thin films. The strain–life fatigue behavior of LIGA Ni thin films is studied by performing fully reversed cyclic microbend experiments that provide insights into cyclic stress/strain evolution and cyclic failure phenomena. The effects of cyclic deformation on the plasticity length-scale parameters are also considered within the context of strain gradient plasticity theories. The implications of the results are then discussed for the analysis of plasticity and cyclic deformation in MEMS structures and other microscale systems.

Study of Small Scale Effects on the Nonlinear Vibration Response of Functionally Graded Timoshenko Microbeams Based on the Strain Gradient Theory

2012 ◽  
Vol 7 (3) ◽  
Author(s):  
R. Ansari ◽  
R. Gholami ◽  
S. Sahmani
Keyword(s):  
Strain Gradient ◽  
Beam Theory ◽  
Functionally Graded ◽  
Strain Gradient Theory ◽  
Gradient Theory ◽  
Length Scale ◽  
Scale Parameters ◽  
Linear And Nonlinear ◽  
Material Length Scale ◽  
Material Length

In the current study, the nonlinear free vibration behavior of microbeams made of functionally graded materials (FGMs) is investigated based on the strain gradient elasticity theory and von Karman geometric nonlinearity. The nonclassical beam model is developed in the context of the Timoshenko beam theory which contains material length scale parameters to take the size effect into account. The model can reduce to the beam models based on the modified couple stress theory (MCST) and the classical beam theory (CBT) if two or all material length scale parameters are taken to be zero, respectively. The power low function is considered to describe the volume fraction of the ceramic and metal phases of the FGM microbeams. On the basis of Hamilton’s principle, the higher-order governing differential equations are obtained which are discretized along with different boundary conditions using the generalized differential quadrature method. The dimensionless linear and nonlinear frequencies of microbeams with various values of material property gradient index are calculated and compared with those obtained based on the MCST and an excellent agreement is found. Moreover, comparisons between the various beam models on the basis of linear and nonlinear types of strain gradient theory (SGT) and MCST are presented and it is observed that the difference between the frequencies obtained by the SGT and MCST is more significant for lower values of dimensionless length scale parameter.

Strain gradient plasticity length scale parameters for LIGA Ni MEMs thin films

2006 ◽  
Vol 441 (1-2) ◽  
pp. 299-307 ◽  
Author(s):  
J. Lou ◽  
P. Shrotriya ◽  
S. Allameh ◽  
T. Buchheit ◽  
W.O. Soboyejo
Keyword(s):  
Thin Films ◽  
Strain Gradient ◽  
Strain Gradient Plasticity ◽  
Length Scale ◽  
Gradient Plasticity ◽  
Scale Parameters

scholarly journals Breaking the barrier to biomolecule limit-of-detection via 3D printed multi-length-scale graphene-coated electrodes

2021 ◽  
Vol 12 (1) ◽  
Author(s):  
Md. Azahar Ali ◽  
Chunshan Hu ◽  
Bin Yuan ◽  
Sanjida Jahan ◽  
Mohammad S. Saleh ◽  
...  
Keyword(s):  
Limit Of Detection ◽  
High Surface ◽  
High Surface Area ◽  
Length Scale ◽  
Graphene Nanoflakes ◽  
Sensing Platform ◽  
Low Concentrations ◽  
Ultralow Concentrations ◽  
3D Printed ◽  
Coated Electrodes

AbstractSensing of clinically relevant biomolecules such as neurotransmitters at low concentrations can enable an early detection and treatment of a range of diseases. Several nanostructures are being explored by researchers to detect biomolecules at sensitivities beyond the picomolar range. It is recognized, however, that nanostructuring of surfaces alone is not sufficient to enhance sensor sensitivities down to the femtomolar level. In this paper, we break this barrier/limit by introducing a sensing platform that uses a multi-length-scale electrode architecture consisting of 3D printed silver micropillars decorated with graphene nanoflakes and use it to demonstrate the detection of dopamine at a limit-of-detection of 500 attomoles. The graphene provides a high surface area at nanoscale, while micropillar array accelerates the interaction of diffusing analyte molecules with the electrode at low concentrations. The hierarchical electrode architecture introduced in this work opens the possibility of detecting biomolecules at ultralow concentrations.

scholarly journals AN INVESTIGATION OF THE STRUCTURAL STRENGTH OF TRANSTIBIAL SOCKETS FABRICATED USING CONVENTIONAL METHODS AND RAPID PROTOTYPING TECHNIQUES

2019 ◽  
Author(s):  
Brittany Pousett ◽  
Aimee Lizcano ◽  
Silvia Ursula Raschke
Keyword(s):  
3D Printing ◽  
Rapid Prototyping ◽  
Ultimate Strength ◽  
Stance Phase ◽  
Structural Strength ◽  
Static Strength ◽  
Strength Test ◽  
Manufacturing Method ◽  
Strength Tests ◽  
3D Printed

BACKGROUND: Rapid Prototyping is becoming an accessible manufacturing method but before clinical adoption can occur, the safety of treatments needs to be established. Previous studies have evaluated the static strength of traditional sockets using ultimate strength testing protocols outlined by the International Organization for Standardization (ISO). OBJECTIVE: To carry out a pilot test in which 3D printed sockets will be compared to traditionally fabricated sockets, by applying a static ultimate strength test. METHODOLOGY: 36 sockets were made from a mold of a transtibial socket shape,18 for cushion liners with a distal socket attachment block and 18 for locking liners with a distal 4-hole pattern. Of the 18 sockets, 6 were thermoplastic, 6 laminated composites & 6 3D printed Polylactic Acid. Sockets were aligned in standard bench alignment and placed in a testing jig that applied forces simulating individuals of different weight putting force through the socket both early and late in the stance phase. Ultimate strength tests were conducted in these conditions. If a setup passed the ultimate strength test, load was applied until failure. FINDINGS: All sockets made for cushion liners passed the strength tests, however failure levels and methods varied. For early stance, thermoplastic sockets yielded, laminated sockets cracked posteriorly, and 3D printed socket broke circumferen-tially. For late stance, 2/3 of the sockets failed at the pylon. Sockets made for locking liners passed the ultimate strength tests early in stance phase, however, none of the sockets passed for forces late in stance phase, all broke around the lock mechanism.  CONCLUSION: Thermoplastic, laminated and 3D printed sockets made for cushion liners passed the ultimate strength test protocol outlined by the ISO for forces applied statically in gait. This provides initial evidence that 3D printed sockets are statically safe to use on patients and quantifies the static strength of laminated and thermoplastic sockets. However, all set-ups of sockets made for locking liners failed at terminal stance. While further work is needed, this suggests that the distal reinforcement for thermoplastic, laminated and 3D printed sockets with distal cylindrical locks may need to be reconsidered. LAYMAN’S ABSTRACT 3D printing is a new manufacturing method that could be used to make prosthetic sockets (the part of the prosthesis connected to the individual). However, very little is known about the strength of 3D printed sockets and if they are safe to use. As Prosthetists are responsible for providing patients with safe treatments, the strength of 3D printed sockets needs to be established before they can be used in clinical practice. The strength of sockets made using current manufacturing methods was compared to those made using 3D printing. Strength was tested using the static portion of the ISO standard most applicable for this situation which outlines the forces a socket must take at 2 points in walking–when the foot is placed on the ground (early stance) and when the foot pushed off the ground (late stance). Sockets made for two prosthetic designs (cushion and locking) were tested to determine if one is safer than the other. All sockets made for cushion liners passed the standard for forces applied statically. However, different materials failed in different ways. At early stance, thermoplastic sockets yielded, laminated composite sockets cracked and 3D printed sockets broke circumferentially. At late stance other components failed 2/3 of the time before the sockets were affected. This provides initial evidence that sockets made for cushion liners are statically safe to use on patients. Sockets made for locking liners failed around the end, showing that 3D printing should not be used to create sockets with the design tested in this study. Article PDF Link: https://jps.library.utoronto.ca/index.php/cpoj/article/view/31008/24937 How to Cite: Pousett B, Lizcano A, Raschke S.U. An investigation of the structural strength of transtibial sockets fabricated using conventional methods and rapid prototyping techniques. Canadian Prosthetics & Orthotics Journal. 2019; Volume2, Issue1, No.2. DOI: https://doi.org/10.33137/cpoj.v2i1.31008 CORRESPONDING AUTHORBrittany Pousett, BSc, MSc, Certified Prosthetist,Head of Research at Barber Prosthetics Clinic,540 SE Marine Dr, Vancouver, British Colombia V5X 2T4, Canada.Email: [email protected]

Size-Dependent Pull-In Instability of Hydrostatically and Electrostatically Actuated Circular Microplates

2012 ◽  
Vol 8 (2) ◽  
Author(s):  
R. Ansari ◽  
R. Gholami ◽  
V. Mohammadi ◽  
M. Faghih Shojaei
Keyword(s):  
Boundary Conditions ◽  
Governing Equation ◽  
Couple Stress Theory ◽  
Gradient Elasticity ◽  
Modified Couple Stress Theory ◽  
Distributed Model ◽  
Length Scale ◽  
Scale Parameters ◽  
Various Boundary Conditions ◽  
Size Dependent

This article is concerned with the development of a distributed model based on the modified strain gradient elasticity theory (MSGT), which enables us to investigate the size-dependent pull-in instability of circular microplates subjected to the uniform hydrostatic and nonuniform electrostatic actuations. The model developed herein accommodates models based on the classical theory (CT) and modified couple stress theory (MCST), when all or two material length scale parameters are set equal to zero, respectively. On the basis of Hamilton's principle, the higher-order nonlinear governing equation and corresponding boundary conditions are obtained. In order to linearize the nonlinear equation, a step-by-step linearization scheme is implemented, and then the linear governing equation is discretized along with different boundary conditions using the generalized differential quadrature (GDQ) method. In the case of CT, it is indicated that the presented results are in good agreement with the existing data in the literature. Effects of the length scale parameters, hydrostatic and electrostatic pressures, and various boundary conditions on the pull-in voltage and pull-in hydrostatic pressure of circular microplates are thoroughly investigated. Moreover, the results generated from the MSGT are compared with those predicted by MCST and CT. It is shown that the difference between the results from the MSGT and those of MCST and CT is considerable when the thickness of the circular microplate is on the order of length scale parameter.

scholarly journals Capturing wave dispersion in heterogeneous and microstructured materials through a three-length-scale gradient elasticity formulation

2018 ◽  
Vol 27 (5-6) ◽  
Author(s):  
Dario De Domenico ◽  
Harm Askes ◽  
Elias C. Aifantis
Keyword(s):  
Gradient Elasticity ◽  
Wave Dispersion ◽  
Length Scale ◽  
Lattice Systems ◽  
Scale Parameters ◽  
Atomistic Models ◽  
Generalized Continuum ◽  
Long Range Interactions ◽  
Additional Strain ◽  
Local Lattice

AbstractLong-range interactions occurring in heterogeneous materials are responsible for the dispersive character of wave propagation. To capture these experimental phenomena without resorting to molecular and/or atomistic models, generalized continuum theories can be conveniently used. In this framework, this paper presents a three-length-scale gradient elasticity formulation whereby the standard equations of elasticity are enhanced with one additional strain gradient and two additional inertia gradients to describe wave dispersion in microstructured materials. It is well known that continualization of lattice systems with distributed microstructure leads to gradient models. Building on these insights, the proposed gradient formulation is derived by continualization of the response of a non-local lattice model with two-neighbor interactions. A similar model was previously proposed in the literature for a two-length-scale gradient formulation, but it did not include all the terms of the expansions that contributed to the response at the same order. By correcting these inconsistencies, the three-length-scale parameters can be linked to geometrical and mechanical properties of the material microstructure. Finally, the ability of the gradient formulation to simulate wave dispersion in a broad range of materials (aluminum, bismuth, nickel, concrete, mortar) is scrutinized against experimental observations.

scholarly journals Assessment of Blade Strength for Small Wind Turbine Applications

2020 ◽  
Vol 160 ◽  
pp. 01007
Author(s):  
K. Zawadzki ◽  
C. Kuzalski ◽  
W. Śmiechowicz ◽  
M. Tarkowski ◽  
D. Kądrowski ◽  
...  
Keyword(s):  
Structural Integrity ◽  
Static Strength ◽  
Point Of View ◽  
Anisotropic Structure ◽  
New Materials ◽  
Strength Tests ◽  
Small Wind Turbines ◽  
Production Techniques ◽  
3D Printed ◽  
Structural Failures

Small Wind Turbines (SWTs) are an increasingly developing Renewable Energy Source, thanks to the gradual popularisation of the prosumer energy generation approach. This, however, requires maximum safety of the machine, working next to households. Reliability is also necessary from the financial point of view, as SWTs should withstand 20 - 30 years of operation without any serious failure to ensure investment profitability. The weakest SWT element is arguably its most exposed one - the rotor - hence the important role played by the blade strength tests. The experimental analysis becomes preferable with increasing popularity of new materials (composites) and production techniques (additive manufacturing). This paper sets out to develop a test stand for static strength examination of 3D-printed SWT blades. This kind of objects is often considered as more vulnerable to structural failures than those created via machining techniques, due to their anisotropic structure, so ensuring structural integrity is crucial for safety reasons.

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