Test configuration
Hydrogel (Beads)
Hydrogels beads are micro-sized particles made from natural or synthetics polymers.
About this material
Hydrogels beads are micro-sized particles made from natural or synthetics polymers. They are used in various applications such as biomedical, drug delivery and biological studies.
Test configurations (7)
Test configuration
Dynamic Mechanical Analysis
Test configuration
Swelling and Contraction
Test configuration
Temperature Control
Test configuration
External Analog Sensors
Test configuration
Digital Image Correlation (DIC)
Test configuration
Camera Feed
Case studies (1)
Related resources (2)
FAQ
What is Young's modulus E?
Intrinsic mechanical property of a material independent of its geometry. From the slope of the stress vs. strain graph during an unconfined compression and considering the geometry of the sample, we can calculate the Young's modulus.
What is Poroelasticity?
Property of an elastic or viscoelastic material with an incompressible free fluid phase. When such a material is put under stress, fluid is released from the solid matrix. The frictional drag generated from the movement of the fluid through the matrix affects the mechanical behavior of such material. These materials are normally tested in a bath of fluid.
Mach-1 Analysis – Poroelastic Model in Unconfined Compression – Parameters
Mach-1 Analysis – Poroelastic Model in Confined Compression – Parameters
Mach-1 Analysis – Poroelastic Model in Confined Compression – Example
Mach-1 Analysis – Poroelastic Model in Unconfined Compression – Cartilage
Mach-1 Analysis – Poroelastic Model in Unconfined Compression – Example
LAB MODULE – Torsion of Disk-Shaped Samples – Student Version
What is the shear stress?
The shear stress is the component of the mechanical stress causing deformation of a material by slippage along a plane or planes parallel to the imposed stress. Shear stress arises from shear forces, which are pairs of equal and opposing forces acting on opposite sides of an object. Units are in Pa.
t =F/A, where t = the shear stress, F = the force applied and A = the cross-sectional area of material with area parallel to the applied force vector.
Lab Module — Torsion of disk-shaped samples
LAB MODULE – Torsion of Bone – Student Version
LAB MODULE – Torsion of Disk-Shaped Samples – Student Version
What is the shear modulus?
The shear modulus G is a mechanical property of a material. It is independent of the material geometry. It represents the stiffness of a material under a force parallel to one of its surfaces while its opposite face experiences an opposite force. The shear modulus G is described as the shear stress over the shear strain. The shear modulus is extrapolated from the linear regression between shear stress at equilibrium and shear strain.
Lab Module — Torsion of disk-shaped samples
LAB MODULE – Torsion of Bone – Student Version
LAB MODULE – Torsion of Disk-Shaped Samples – Student Version
How does the "Elastic Model on Spherical Sample" feature works?
This tool allows for the computing and visualizing of the shear modulus (MPa) from an unconfined compression test performed using a flat indenter on a spherical sample (Figure 1).
Results analysis is performed considering small deformation of a perfectly spherical sample (with uniform elastic material properties) tested in unconfined compression between two flat platens. Curve fitting is based on Gauthier et al., 2004 who used the Hertz model predicting the force exerted by a rigid spherical body under small deformation (less than 10%) which is given by the equation (attached), where F(r) is the force exerted by the sphere when the distance separating the compressing platen surface from the bottom platen is r (and r ˂ 2 R0), u is the shear modulus and R0 is the bead's initial radius.
The radius of the spherical sample has to be specified in order to calculate the material properties. The error on the estimation of the best curve representing the compression curve is calculated using the root of the mean squares (RMS) method and is displayed under “RMSE”. For example, (Figure 2) shows parameters used for the “Stress Relaxation” (Mach-1 Motion) function in an unconfined compression protocol on a single spherical bead. Corresponding results are shown in (Figure 1).
Results analysis is performed considering small deformation of a perfectly spherical sample (with uniform elastic material properties) tested in unconfined compression between two flat platens. Curve fitting is based on Gauthier et al., 2004 who used the Hertz model predicting the force exerted by a rigid spherical body under small deformation (less than 10%) which is given by the equation (attached), where F(r) is the force exerted by the sphere when the distance separating the compressing platen surface from the bottom platen is r (and r ˂ 2 R0), u is the shear modulus and R0 is the bead's initial radius.
The radius of the spherical sample has to be specified in order to calculate the material properties. The error on the estimation of the best curve representing the compression curve is calculated using the root of the mean squares (RMS) method and is displayed under “RMSE”. For example, (Figure 2) shows parameters used for the “Stress Relaxation” (Mach-1 Motion) function in an unconfined compression protocol on a single spherical bead. Corresponding results are shown in (Figure 1).
Mach-1 Analysis – Elastic Model on Spherical Sample – parameters
Mach-1 Analysis – Elastic Model on Spherical Sample – Equation
Mach-1 Analysis – Elastic Model on Spherical Sample – Example
How does the "Sinusoid" model works?
This feature is used to obtain the Frequency, Amplitude and Offset of a sinusoidal signal. A blue line displays the theoretical sinusoid with the Frequency, Amplitude and Offset obtained (Figure 1). The values of the Frequency, Amplitude and Offset are indicated in the "Results" field. The units vary according to the graph’s axes.
This feature can also be used for sinusoidal stimulus-response analysis. Sinusoidal stimulus shall be selected on the x-axis and the sinusoidal response on the y-axis. The Modulus is the ratio of the response Amplitude over the stimulus Amplitude. The Phase is the phase difference between the response and the stimulus. The Modulus’ is computed as the Modulus*Cos(Phase) and the Modulus” is computed as the Modulus*Sin(Phase). A blue line displays the theoretical sinusoidal stimulus-response with the Frequency, Modulus and Phase obtained (Figure 2). The values of the Modulus and Phase are indicated in the “Results” field. The units vary according to the graph’s axes.
One use for this feature would be to compute material properties by multiplying the Modulus obtained by the appropriate geometric factors. For example, the Young’s Modulus can be obtained during uniaxial compression or tension on cylindrical sample with t/pi*r2 as the geometric factor, t is the thickness and r is the radius of the sample.
Mach-1 Analysis – Sinusoid – Example for stimulus-response analysis
How does the creep function works?
The Creep function moves a stage until a predefined load variation (Load Target (relative to initial load)) is reached and maintains this loading through real-time closed-loop PID adjustment of the stage position. This function can be used, for example, to study the deformation of a sample under constant loading. Note that tuning a PID requires a reasonable amount of closed-loop system understanding. A set of PID parameters optimized for a particular experimental configuration will probably be inappropriate for a different configuration and could even create system instabilities (oscillations) that can result in damage to the system.
Parameters:
STAGE AXIS - On multi-axis systems, the user must specify which axis will perform the “Creep”.
DIRECTION - Specify if the stage has to start moving in the positive or negative direction. With a positive displacement, a vertical stage will move down (compression), a horizontal stage will move right, and a rotation stage will move clockwise. Enter a negative value for stage displacements in opposite directions.
STAGE VELOCITY, MM/S - Specify the speed at which the stage will move. Refer to the specifications of your Mach-1™ model to learn about the velocity range allowed. In Mach-1 Motion, the speed is always specified in absolute value terms.
RELATIVE LOAD TARGET, GF OR N - Specify the relative amount of load to be applied and maintained on the sample. When a value is entered, the stage will initiate its movement until a change in load of that magnitude is reached. The value for Relative Load Target is specified in absolute value terms.
CREEP TIME, SEC - This is the time period during which the relative loading will be maintained. Note that after this period, the final stage position will be maintained.
P GAIN - This is the Proportional gain of the PID control loop. This is the main parameter that drives the feedback loop. Our experiments revealed that a good starting point for the optimization of this parameter is given by P = 0.001 (and I = 0), then raising P in logarithmic increments (0.01, 0.1, 1) until a satisfactory amplitude in reached. The higher the P value, the faster the error will be corrected, however if the P is made too large, the error can go negative (actual load > desired load) which may start a process where the stage starts to oscillate between speeding up and slowing down. This oscillation can result in the motor control system going unstable. A simple way to eliminate this instability would be to decrease P until the oscillation stops.
I GAIN - This is the Integral gain of the PID control loop. Integral control sums the error from each position update then multiplies the sum by the Integral gain, I. Our experiments revealed that for most creep tests, best results are achieved with I = 0. If a residual error exists while holding a load, the I value can also be incrementally increased until the error disappears.
What is viscoelasticity?
Property of a material to exhibit both viscous and elastic characteristics when undergoing deformation. Such material will show time-dependent mechanical behavior.
LAB MODULE – Torsion of Disk-Shaped Samples – Student Version
What is the strain rate?
Change in strain or deformation of a material with respect to time.
What is the elasticity?
Property of a material to deform under load or strain and to return to its original shape when the stress is released.
LAB MODULE – Unconfined Compression of Hydrogel Disks – Student Version
What is the stiffness K?
A structural property of a sample. By plotting force vs. displacement during an unconfined compression and extracting the slope, we obtain the stiffness of the sample. In Mach-1 Analysis, the slope is in gram-force per mm (gf/mm). The gram-force is 1 gram multiplied by the acceleration due to gravity on Earth, exactly 9.80665 m/s².