skip to main content
US FlagAn official website of the United States government
dot gov icon
Official websites use .gov
A .gov website belongs to an official government organization in the United States.
https lock icon
Secure .gov websites use HTTPS
A lock ( lock ) or https:// means you've safely connected to the .gov website. Share sensitive information only on official, secure websites.

Explore Research Products in the PAR
It may take a few hours for recently added research products to appear in PAR search results.


Title: Micromechanics Study on Actuation Efficiency of Hard-Magnetic Soft Active Materials
Abstract Hard-magnetic soft active materials have drawn significant research interest in recent years due to their advantages of untethered, rapid and reversible actuation, and large shape change. These materials are typically fabricated by embedding hard-magnetic particles in a soft matrix. Since the actuation is achieved by transferring the microtorques generated on the magnetic particles by the applied magnetic field to the soft matrix, the actuation depends on the interactions between the magnetic particles and the soft matrix. In this paper, we investigate how such interactions can affect the actuation efficiency by using a micromechanics approach through the representative volume element simulations. The micromechanics reveals that particle rotations play an essential role in determining the actuation efficiency, i.e., the torque transmission efficiency. In particular, a larger local particle rotation in the matrix would reduce the effective actuation efficiency. Micromechanics simulations further show that the efficiency of the torque transmission from the particles to the matrix depends on the particle volume fraction, the matrix modulus, the applied magnetic field strength, as well as the particle shape. Based on the micromechanics simulations, a simple theoretical model is developed to correlate the torque transmission efficiency with the particle volume fraction, the matrix modulus, as well as the applied magnetic field strength. We anticipate this study on the actuation efficiency of hard-magnetic soft active materials would provide optimization and design guidance to the parameter determination for the material fabrication for different applications.  more » « less
Award ID(s):
1943070 1939543
PAR ID:
10214957
Author(s) / Creator(s):
; ; ;
Date Published:
Journal Name:
Journal of Applied Mechanics
Volume:
87
Issue:
9
ISSN:
0021-8936
Format(s):
Medium: X
Sponsoring Org:
National Science Foundation
More Like this
  1. ; ; ; ; ; (, Smart Materials and Structures)
    Abstract Magnetoactive elastomers (MAEs) are capable of large deformation, shape programming, and moderately large actuation forces when driven by an external magnetic field. These capabilities enable applications such as soft grippers, biomedical devices, and actuators. To facilitate complex shape deformation and enhanced range of motion, a unimorph can be designed with varying geometries, behave spatially varying multi-material properties, and be actuated with a non-uniform external magnetic field. To predict actuation performance under these complex conditions, an analytical model of a segmented MAE unimorph is developed based on beam theory with large deformation. The effect of the spatially-varying magnetic field is approximated using a segment-wise effective torque. The model accommodates spatially varying concentrations of magnetic particles and differentiates between the actuation mechanisms of hard and soft magnetic particles by accommodating different assumptions concerning the magnitude and direction of induced magnetization under a magnetic field. To validate the accuracy of the model predictions, four case studies are considered with various magnetic particles and matrix materials. Actuation performance is measured experimentally to validate the model for the case studies. The results show good agreement between experimental measurements and model predictions. A further parametric study is conducted to investigate the effects of the magnetic properties of particles and external magnetic fields on the free deflection. In addition, complex shape programming of the unimorph actuator is demonstrated by locally altering the geometric and material properties. 
    more » « less
  2. ; ; (, American Society of Mechanical Engineers)
    Abstract In this research, we investigate multi-stimuli responsive multimaterial structures by combining shape memory polymers (SMPs) with magnetoactive fillers. Our objective is to design 3D-printed composites with local and global magnetoactive filler gradients, which exhibit complex shape actuation under magnetic and thermal fields. We first carry out a rheological study of SMP dispersions containing surface-treated magnetic particles to understand the effect of magnetic particle surface treatment, additives content, and shear rate on the complex flow behavior. Our findings reveal that dispersions filled with surface-treated magnetic particles exhibit enhanced shear thinning behavior and shape integrity compared to unfunctionalized dispersions. The improved rheological behavior and shape integrity are important results that indicate that PEG-functionalized SMP composites are promising candidates for direct ink printing. To create complex actuation, a 3D printing system is designed in a way that the magnetic particle-SMP dispersions are oriented using both shear and an external magnetic field, enabling a local angular gradient of magnetic particles. In addition, a global gradient is designed-in by varying the volume fraction of magnetic particles in the SMP suspensions. By adjusting the local and global gradients of magnetic particles within the SMP, different actuation patterns can be achieved. SEM analysis confirms the presence of the global gradient in iron oxide particles and their alignment along the magnetic field direction post-printing. Vibrating Sample Magnetometry (VSM) studies reveal an improved mass magnetization along the length of the printed samples, moving away from the printing origin. In addition, the iron oxide weight percent in the samples increases from 2.5 wt.% at the printing origin to 12.5wt.% at the end, creating a pronounced Fe3O4 global gradient. These findings contribute to the development of advanced stimuli-responsive materials with tunable properties for various applications where complex shape actuation is required, including soft robotics, and biomedical devices. 
    more » « less
  3. ; ; (, Proceedings of the International Design Engineering Technical Conferences & Computers and Information in Engineering Conference)
    null (Ed.)
    Ferromagnetic soft materials can generate flexible mobility and changeable configurations under an external magnetic field. They are used in a wide variety of applications, such as soft robots, compliant actuators, flexible electronics, and bionic medical devices. The magnetic field enables fast and biologically safe remote control of the ferromagnetic soft material. The shape changes of ferromagnetic soft elastomers are driven by the ferromagnetic particles embedded in the matrix of a soft elastomer. The external magnetic field induces a magnetic torque on the magnetized soft material, causing it to deform. To achieve the desired motion, the soft active structure can be designed by tailoring the layouts of the ferromagnetic soft elastomers. This paper aims to optimize multi-material ferromagnetic actuators. Multi-material ferromagnetic flexible actuators are optimized for the desired kinematic performance using the reconciled level set method. This type of magnetically driven actuator can carry out more complex shape transformations by introducing ferromagnetic soft materials with more than one magnetization direction. Whereas many soft active actuators exist in the form of thin shells, the newly proposed extended level set method (X-LSM) is employed to perform conformal topology optimization of ferromagnetic soft actuators on the manifolds. The objective function comprises two sub-objective functions, one for the kinematic requirement and the other for minimal compliance. Shape sensitivity analysis is derived using the material time derivative and the adjoint variable method. Three examples are provided to demonstrate the effectiveness of the proposed framework. 
    more » « less
  4. ; ; ; (, AIP Advances)
    To better understand Magnetic Field Assisted Additive Manufacturing (MFAAM) the effect of a magnetic field on the orientation and distribution of magnetic particles in a molten magnetic composite was studied. Vibrating Sample Magnetometer (VSM) measurements were made on Sr-ferrite/PA12 fused deposition modeling filaments of different packing fraction (5 and 40 wt. %). The rotation of the sample’s magnetic moment upon application of a field perpendicular to the easy axis was monitored with a biaxial VSM above the PA12’s softening temperature. The observed magnetic moment transients depend on the temperature, the applied alignment field, the packing fraction, and the initial field-anneal procedure. Longer field-anneals result in larger time constants and seem to induce a hurdle that prevents complete alignment at low temperatures and/or for small fields. Results indicate the molten composite is a non-Newtonian fluid that can support a yielding stress. Scanning Electron microscopy (SEM) images taken on field-annealed samples at 230 °C show strong chaining with little PA-12 left between individual Sr-ferrite particles suggesting that direct particle to particle interaction is the reason for the observed non-zero yielding stress. The melt viscosity of the composite increases with the number of thermal cycles above the melting temperature (T m ). Room temperature (RT) torque magnetometry measurements show that magnetic anisotropy depends on the field annealing process through induced shape anisotropy contributions originating from magnetic particle agglomerates. 
    more » « less
  5. ; (, Physics of Fluids)
    The stability of a rigid particle in yield stress fluids, comprised of soft particle glasses (SPGs), is investigated in shear flow under an applied external force, such as weight, using particle dynamics simulations. Results provide the critical force threshold, in terms of the dynamic yield stress and the flow strength, required to initiate sedimentation of the rigid particle over a wide range of shear rates and volume fractions. The streamlines of the SPGs show local disturbances when the rigid particle settles. The form of these disturbances is consistent with the microdynamics and microstructure response of the neighboring soft particles of the sedimenting rigid particle. Sedimenting particle induces non-affine displacement to the suspensions at low shear rates and high applied forces, while these dynamical events are localized and suppressed at high shear rates. Stability diagrams, which provide the conditions of the sedimentation of the rigid particle, are presented in terms of the applied force and the shear rate. These individual stability diagrams at each volume fraction map onto a universal stability diagram when the external force is scaled by the dynamic yield stress and shear rate with a ratio of the solvent viscosity to the low-frequency modulus of the SPGs. 
    more » « less
  • Citation Formats
  • MLA
  • APA
  • Chicago
  • BibTeX
  • Save / Share this Record
  • Send to Email