Engineering : Testing


Health Monitoring and Imaging System for Concrete Structures

An assistant professor in civil engineering at the University of Wisconsin-Platteville in partnership with an electrical engineer from New Mexico State University, has developed a comprehensive monitoring system capable of identifying interior defects and stress in concrete structures such as bridges. By combining sensor technology with an ultrasound signal generator, multi-channel data acquisition and proprietary data processing algorithms, the interior conditions in any cross section of a bridge can be visualized in 3D. With this technology, small stress changes in the order of 0.1Mpa and cracks as thin as a human hair are detected. Such a combined system provides competitive advantage over existing methods that solely measure stress changes and rely on installation of strain gauges on the surface or inside concrete structures. These methods only provide for measurement of stress changes at the locations where sensors are placed, creating gaps in the evaluation of stress change. In addition, with current technology, holes must be drilled and patched for sensor placement and bridges must be taken out of service during testing. The proposed technology provides for a more absolute evaluation of not only changes in stress but also identification of cracks, does not require drilling of holes and can be used on in-service bridges, saving time, money and providing a more comprehensive assessment of bridge health.

More Efficient Laminate Analysis

UW–Madison researchers have developed a method for analyzing composite laminate structures that combines the generality of 3-D FEA and efficiency of 2-D FEA whenever it is applicable. The new method works by substituting the laminate layers with much simpler virtual material models having matching characteristics (e.g., overall material properties and relationship between stresses and strains). The updated model can then by analyzed via fully automated 3-D FEA.

The virtual models may be referred to as ABD-equivalent models, as they result in the same ABD stiffness matrices as the real laminate and can act as substitutes if plate-shell assumptions apply.

Dynamic Predictor Improves Machine Control

The researcher now has developed a new dynamic predictor that rapidly and accurately calculates the motion trajectory of a system that is only partially constrained by joint inputs. This dynamic predictor achieves stable and accurate results for stiff systems. To do this, the predictor applies conditions achieving such results at both a first and second joint position at the start and end of a motion time step.

More specifically, the relationship between joints is described as a differential equation to be solved by the predictor. The predictor parameterizes the motion of the unconstrained joints in such a way as to match the conditions the solution needs to satisfy at both the start and end of a motion time step. As this parameterization is expressed by polynomial coefficients, motions of the remaining joints are readily determined by the kinematic predictor.

Movement Predictor for Real-Time Robotics Control

A UW–Madison researcher has developed a mathematical motion predictor for controlling and designing jointed mechanisms.

The predictor uses a system of differential equations describing the rate of change in each moving joint. These equations are solved by direct substitution of the variables with multiterm power series expressions. A linear relationship between coefficients of the same order can be established to form a system of independent and linearly related equations solvable by standard automatic techniques.

New Rheometer and Method for Efficiently Measuring Yield Stress in Biomass

UW–Madison researchers have developed a device and a method for measuring rheological properties of fluid that will effectively determine the yield stress of biomass materials. These measurements do not alter the material sample prior to measurement, allowing for more accurate data results and characterization.

The device comprises a cavity for receiving the fluid, an auger connected with an axial shaft, and a load cell sensor connected to the auger. The sensor measures the force on the auger from the fluid as the auger moves up and down. A linkage interconnected to the sensor translates motion to the auger.

Dielectric Sensor for Stress and Strain Detection

UW–Madison researchers have developed capacitive strain sensors that measure stress and strain based only on dielectric properties. The two parallel plates are affixed to a substrate so that variance in capacitance occurs only due to change in dielectric properties rather than mechanical displacement. The dielectric change is then translated into an indication of stress and strain.

The sensors consist of interlocked electrodes that can be deposited on a rigid or flexible substrate. They can be implemented as single sensing elements or arranged in rosettes of up to eight capacitors to measure dielectric properties along multiple axes at once. The planar geometry of the electrodes makes the sensors compatible with standard complementary metal-oxide semiconductors (CMOS) fabrication processes, so their characteristics may be tailored easily to particular applications. Signal conditioning circuits also may be incorporated on the same substrate to reduce the need for additional external components and simplify the construction process.

Because rosettes are capable of detecting the dielectric response without direct physical contact, they are suspended slightly away from the measured object to eliminate mechanical contact that could disrupt the measurement. The sensors may be interfaced to the material through a thin layer of mineral oil, which reduces mechanical constraints by lubricating the surface. In addition, the oil eliminates moisture effects and minimizes sensitivity loss.

Improved Pressure Plate Extractor for Characterizing Soils

Two UW-Madison civil engineers have now devised an improved, leak-free design for pressure plate extractors. Specifically, their design incorporates a gasket that sits in a channel around the perimeter of the drain plate rather than on top. When the chamber lid is clamped onto the gasket, the gasket expands laterally to tightly engage the drain plate, the side walls of the chamber lid and the pressure chamber base.

Solid-State Strain Sensor That Can Sense Shear and Normal Deformation in Almost Any Dielectric Material

A UW-Madison engineer has now developed a novel class of strain sensors that can sense shear and normal deformation in nearly any dielectric material, without the need for mechanical contact. These new strain sensors are based on electrostriction, a phenomenon in which a material's dielectric properties change with deformation.

The sensor is a solid-state, single-plate device in which pairs of electrodes are positioned in close proximity to the material being measured. As the material deforms and its electrostrictive properties change, this alteration registers as a change in capacitance between paired electrodes. The strain force in the material is then determined by calculating the material’s change in electrostrictive parameters from the change in capacitance.