µTS – Meso Scale Universal Load Frame for Materials Testing 2017-03-15T11:39:23+00:00

“Meso is the new nano.”

– Prof. Peter Hosemann, UC Berkeley

µTS – Meso Scale Under Microscope Universal Load Frame

Psylotech’s µTS is a miniature universal material test system uniquely capable on length scales between nano-indenters and macro universal load frames. Non-contact, local strain measurement on these so-called meso length scales comes from digital image correlation (DIC) and microscopy.

Download a PDF Brochure

Applications

   Extending the life of existing nuclear power plants means verifying alloy strength decades of radiation exposure. The quantity of exposed material is limited. Testing small-scale samples enables statistically relevant studies when available material is limited. It also means less radioactive material in the lab.
The µTS combined with microscopy can be used to study inter-grain interaction in metals. Digital image correlation enables effective surface strain field mapping and optical microscopes offer a convenient, cost effective image capture technique.
visca_medicalDigital Image Correlation and optical microscopy enable local strain measurement on tissues, cells and cellular structures. Psylotech offers a temperature control chamber and a fluid bath to control a sample’s environment. Ask us how we can help develop gripping techniques for your specific application.
21603479_mlLeveraging small scale, the µTS miniature universal load frame can test samples cut through the thickness of a weld. Complete stress strain curves can be obtained from different sections, providing direct correlation of yield and failure strength as a function of weld depth.
Interactions between grains and voids during mechanical loading can be studied with the µTS. For example, consider toughening mechanisms in partially stabilzed zirconia. Correlation coefficient can track microcrack formation and DIC can reveal localized strain changes from the partially stabilized phase closing the crack tip.
12772554_mlThe Materials Genome Project is a guiding principle for government research and grants on par with the National Nanotechnology Initiative. Understanding materials on multiple length scales is a key part of this effort. Substantial work is done on the theoretical and numerical implications of length scale dependence. Psylotech’s µTS is an ideal experimental tool for experimental validation on these length scales.
uTS_Composite_DIC_transIn recent years, there has been a movement to build macroscopic composite mechanical properties from matrix and reinforcement micromechanics models. The µTS enables experimental validation of such multi-scale simulation. A reliable, experimentally validated micromechanics model can generate material properties for any fiber orientation and any loading directions.

The µTS is also appropriate for measuring single fiber stress-strain curves as well as fiber pull-out strength. Ask us how we can help you determine these properties.

homeslider_carMulti-scale µTS testing can provide critical insight into any metal process where properties vary through the thickness, such as casting, welding or heat treating. Small dogbone samples can be wire edm’ed from any orientation within the part, providing highly localized stress-strain data.

The µTS is also a powerful tool for composite materials, enabling the study of particle-matrix interaction on small length scales. These data can be combined with new simulation techniques to infer macro-scale material properties from micromechanics interactions between reinforcing particle and matrix. Through simulation, composites can be optimized virtually, accelerating the product development process.

7816320_mlSmall scale local strain field measurements on the interlocking fibers in paper goods can reveal A better understanding of the mechanisms and structures that strengthen the material can lead to improved products which use less raw material. Improving properties would have economic and environmental implications.
Indeed, the µTS was first developed as a versatile small-scale load frame in an Army Research Laboratory SBIR. (link to about). Meso-scale simulation validation has numerous military implications. For example, consider a Kevlar flack jacket. The µTS can provide data on the fiber strength, fiber/matrix interaction, soft tissue and bone. As such, the impact event can be simulated and the bullet proof vest can be optimized virtually.

Technology

The µTS uniquely accommodates multiple scales in length, speed and force.

  • Length: Constraining out-of-plane motion, the µTS enables effective high magnification digital image correlation, despite depth-of-field limitations in the optical microscopes.
  • Speed: The direct-drive ballscrew actuator enables speeds covering 9 orders of magnitude.  High speed enables effective load control, rate dependent studies and creep or stress relaxation tests.
  • Force: Proprietary ultra high resolution sensor technology provides 100x higher resolution compared to strain gaged alternatives.
Click here to contact us
µTS Iso Image

Grips

µTS

As a universal test system, the µTS implements a T-slot interface for different kinds of grips. The triangle/flat interface geometry ensures accurate rotational alignment. Available standard grips include tension, compression, beam bending and mixed-mode Arcan. Ask us how custom grips can be designed for your specific needs.

Wrap Around Tension

Clamping a specimen on its top and bottom surfaces can lead to out of plane motion during loading. The wrap around tension grips hold the sample on surfaces perpendicular to the observation plane and have been effective in keeping the specimen in plane. As an added benefit, specimens can be very quickly mounted in the wrap around grips.

Clamped Tension

Some materials, like film or chopped fiber composites, are not conducive to the wrap-around grip geometry. Clamping grips can be used in these cases. A vertical micrometer screw adjustment can compensate causes out of plane motion. Also, a single clamping screw eliminates asymmetric clamping torque.

Arcan

The Arcan grip geometry enables mixed-mode loading from a uniaxial load frame. Rotating the grips controls the ratio of pure shear to pure axial strain. This technique takes full advantage of local strain measurement via digital image correlation.

Compression

The compression platens implement a lightly sprung shelf to hold the sample before load is applied. Under load, the light spring easily deforms as the specimen expands

Beam bending

Three and Four point bending fixtures are available. All but one contact point is on a hardened steel roller. The fixed contact point prevents translation, which can give false compliance readings when using compliance to monitor crack growth. Both 3- and 4-point fixtures implement the same lightly sprung shelf as the compression platens.

Options

The modularity of the µTS is as flexible as it is powerful. Below are some of the easily configured options.

µTS

Low force load cell

100N version of the 1.6 kN load cell provides finer force resolution. Ask us about force resolution down to 100 nano Newtons.

Increased Speed

A higher pitch ball-screw, increased motor stack, or higher input voltage can produce speeds up to 250 mm/sec, up from the 80 mm/sec of the stock system.

Extended Stoke

The 40mm stock instrument stroke can be extended substantially, depending on experimental need.

Environmental Chamber

Temperatures between -100C and 200C can be controlled via the optional environmental chamber. Higher temperatures are also available. Low temperatures require liquid nitrogen.

SEM

The µTS can be vacuum hardened for use in scanning electron microscopes. Please note, rastering time as well as spacial and temporal drift complicate DIC with SEM images. Optical microscopy does not have these limitations.

Centering X-stage

A secondary positioning stage keeps any specimen inside the microscope field of view, regardless of the amount of deformation.

Simplified Displacement Sensor

As a cost saving measure, the rotary encoder and ball screw pitch can be used to infer displacements in lieu of the high resolution local displacement sensor.

Sub-10nm Positioning

With a 22 bit rotary encoder mounted to the motor, a 1mm pitch ball screw gives ~238 picometers of linear resolution. Noise of the sensor and tuning jitter bring the closed loop error to under 10nm linearly.

Complete Turnkey Package

Psylotech can provide a complete DIC package, including an Olympus BXFM boom-mounted microscope, Correlated Solutions Vic2D software, a vibration isolation table and a 4 MP USB3.0 camera.

Confocal Raman Microscope

Psylotech’s µTS has been integrated into a Witec confocal Raman microscope. The Psylotest control software controls the microscope stage for specimen centering.

Tension-Torsion Actuator

An extra motor is added to the fixed side of the load frame in addition to a force-torque load cell in order to facilitate axial and torsion loading.

Differentiation

Dimensions in mm

The µTS offers sophisticated motion control and a high degree of precision. It is a versatile instrument, enabling a broad variety of experimental techniques. Designed for experimentalists, careful attention to details include:

  • Ball Screw

    The µTS incorporates a direct drive ball screw, rather than simple lead screws driven through a gearbox. The result is less friction, improved motion control and less maintenance. Moreover, lead screw actuators are typically limited to a narrow range of speeds.

  • Speed

    Alternative lead screw systems are typically limited to a narrow range of speeds. The direct drive ballscrew covers 9 orders of magnitude in speed. It can move as fast as a macro sized servohydraulic load frame or as slow as grass growing on a hot summer’s day. High speed enables versatility for more types of testing, including:

    -Rate dependent studies
    -Step load tests, such as creep or stress relaxation
    -Effective load control
    -Fatigue

  • Out-of-plane motion

    In the µTS, the fixed cross-head, T-slot grip adapter, and load cell are integrated into a single part cut from a solid block of 17-4. This integration contributes to quality in situ image capture under high microscope magnification. Eliminating tolerance stack-up controls out-of-plane motion. The integration also greatly simplifies the system alignment procedure.

    To further control out-of-plane motion, dual linear guides are symmetrically placed in the loading plane. Any moments from frictional effects are balanced and do not contribute to pitch or yaw. Previous designs placed linear guides below the loading plane, causing focus problems under high microscope magnification.

  • Displacement Sensor

    The µTS monitors displacement on axis with the specimen. Alternative systems implement off-axis measurements, such that small pitch or yaw inevitable in real-world experiments show up as false displacement readings. In certain cases, rotary position and pitch are also used to infer displacement.

    With the high-resolution on-axis displacement sensor, Psylotech has achieved better than 5 nm closed loop position control based on feedback from the cross-head displacement sensor. Such control is possible from a large stroke ball-screw actuator, because the feedback sensor measures displacement downstream of the screw in the load train.

  • Psylotest Control Software

    The µTS control software is written in LabVIEW. It features test-segment specific digital filtering and integrated camera triggering, simplifying data and DIC image coordination. Advanced users have the option to modify the program to integrate external systems.

  • Centering Stage

    Large deformations can cause a specific area of interest to exit the microscope’s field of view during an experiment. Opposing left/right handed screws can mitigate this problem, but such a configuration exacerbates he centering problem for beam bending samples. Also, what happens when the area of interest is not in the center of the sample?

    The µTS can be configured with a centering stage. The actuator of this secondary stage is slaved to the main system actuator such that any ratio of motion can be achieved. Relative cross-head motion is not tied to 50/50, and even beam bending samples can be maintained within the field of view.

  • Load Cell

    The µTS leverages proprietary Psylotech technology with 400 mV/V sensitivity compared to 2 mV/V from strain gauged alternatives typically found in universal load frames. The increased sensitivity means about 100x higher resolution, enabling multiple force scale experiments. For example, the stock 1.6 kN load cell can be used on tests where one would normally use a 16 N load cell. Advanced users could leverage this high sensitivity to enable new experiments, such as crack length from compliance or replacing acoustic sensors in composite tests.

Video

Blog

Meso-Scale Thermomechanical Validation

By | December 8th, 2016|Categories: Meso-Scale, Under Microscope Testing|Tags: , , , |

With the advances we've made in under-microscope mechanical testing, it had become apparent that temperature is an important next frontier to expand into. We are happy to announce the launch of a temperature chamber attachment [...]

Psylotest Control Facilitates Data Syncing

By | March 31st, 2015|Categories: Under Microscope Testing|Tags: , , , , , |

Reducing Time to Integrated Data Analysis with External Systems One challenge that can add hours of headache to analyzing load frame and image data together is syncing the load to the image strains. With our [...]

Pricing

Turnkey system package includes microscope, camera, DIC software, secondary x-stage, and vibration isolating optics table
Click for a configuration matrix

About

The core motion control technologies for the µTS were developed in an Army Research Lab WMRD SBIR. Collaboration with Prof. Ioannis Chasiotis at the University of Illinois Urbana-Champaign was critical to that effort. The goal was to apply lessons learned by the Chasiotis group, making them commercially accessible and more user-friendly. In the process, Psylotech added its high resolution sensor technologies and developed a near-nano scale positioning ball screw actuator to create the µTS.

In the rush to understanding the nano scale, six orders of magnitude in length scale were glossed over. The µTS takes advantage of digital image correlation for local strain measurement on these “meso” length scales between 10 mm and 5 nm.