Recent advances in the ultrasonic polar scan method for characterizing (degraded) fiber reinforced plastics

The ultrasonic polar scan (UPS) technique originated in the 1980's as a sophisticated method for inspecting composites. However, it is only in recent times that the true capabilities and strengths of the UPS methodology have been evidenced through experiment and simulation. Nowadays, the UPS method exists in different versions which led to several novel applications in the field of material inspection and characterization. This contribution gives an overview of our recent advances

\u3cem\u3eEucosma giganteana\u3c/em\u3e (Riley) and \u3cem\u3eSliphium perfoliatum\u3c/em\u3e L., Morphological Variation in an Insect-Plant Association in Eastern South Dakota

Silphium perfoliatum L., cup plant, has potential as a new multi-purpose crop. It is pollinator-friendly and has biodiversity enhancement, conservation, economic, and medical potential. In eastern South Dakota, S. perfoliatum can produce more than 20 Mg (million grams) ha-1 of biomass and 0.09 Mg ha-1 of seed in agronomic plantings. The giant eucosma moth, Eucosma giganteana (Riley), is a major pest of agronomic S. perfoliatum in the region. We provide a summary of this insect and its association with its host. Our experimental objectives were to determine if the frequency of rhizome occupation by late instar larvae and if their final prepupal size were influenced by plant genetic or environmental effects. In October 2009, several individual plants from each of 32 half-sib families were removed from the field. Rhizomes, proaxes, and shoots were examined for the presence of larvae. Each larva was counted and measured for total length, width, thoracic tergite length, head length, and head width. Significant differences were found among half-sib families and between locations for frequency of shoot infestation, degree of crown and rhizome feeding, number of larvae per shoot, and larval morphometrics. The parasitoid Bracon cf. mellitor Say (Hymenoptera: Braconidae) was found parasitizing larvae feeding in floral meristems, but no parasitism was found in larvae in the crown or rhizomes

Seed Set and Seed-Insect Interactions in Natural and Cultivated Populations of Purple Prairie Clover

Purple prairie clover (Dalea purpurea Vent.) is a common native legume on dry prairies throughout the central USA and Canada. Seed set in natural populations can be very low, and the reason(s) are not well known. Our objectives were: 1) determine seed set in natural and cultivated populations of purple prairie clover in eastern SD, and 2) identify seed predators and parasitoids associated with natural and cultivated populations. Collection of inflorescences occurred on the South Dakota State University Oak Lake Field Station (OLFS), and from a cultivated population in McCrory Gardens at Brookings, SD. At OLFS, normal seed set was 10% compared with 60% for the McCrory Gardens population. Frequency of unfertilized ovules was about 25%, and seed predation was 55% at OLFS compared with 24% unfertilized ovules and 23% seed predation at McCrory Gardens. The most common seed predators were Kissingeria capitone (Kissinger) and an unidentified midge, Contarinia sp. (Cecidomyiidae). The bruchid beetle Acanthoscelides seminulum (Horn) had much lower seed predation rates. The most common parasitoid reared from beetle larvae was Lyrcus incertus (Ashmead). The chalcidoid wasps Baryscapus sp. and Aprostocetus marylandensis (Girault) attacked midge larvae. A few individuals of Bracon sp. and Inostemma sp., hosts unknown, were also collected from immature inflorescences. This study identified a previously unknown guild of insects associated with inflorescences in purple prairie clover and revealed reasons for a paucity of viable seed production in natural populations

Time-of-flight recorded pulsed ultrasonic polar scan for elasticity characterization of composites

In its orginal configuration, the pulsed ultasonic polarscan (P-UPS) mainly focussed on elastic material characterization through the inversion of amplitude landscape measurements. However, for several materials, special attention is required as minima in the transmission amplitudes do not exactly coincide with critical angles calculated from the Christoffel equations. Consequently, other means to extract the information on elastic moduli from P-UPS measurements are being investigated. In the present paper, we report on the use of time-of-flight ultrasonic polarscan (TOF-UPS) simulations as a new means of material characterization. Previous TOF inversions, although successful, were based on bulk wave approximations, which are not longer valid for thin materials. Our first inversion results on numerical cases demonstrate the usefulness of the new developed technique and highlight the added value compared to the bulk wave approximation

Matching spectroscopy with the ultrasonic polar scan for advanced NDT of composites

The Pulsed Ultrasonic Polar Scan (P-UPS) is a powerful technique for characterizing anisotropic materials like fiber reinforced plastics. A time-domain analysis of the ultrasonic signals yields amplitude and time-of-flight polar diagrams that provide a fingerprint of the local stiffness properties. Though, this simple analysis ignores a lot of information contained in the ultrasonic signals. In this study, we propose to use the P-UPS technique in combination with the spectroscopic analysis of broadband pulses, to obtain plane wave transmission spectra for all in-plane polar angles. This allows us to combine on one hand the strengths of the P-UPS technique, that does not require a priori knowledge about the sample anisotropy, and on the other hand the frequency-domain analysis that utilizes information contained in the broadband pulses

Towards a phased array based ultrasonic polar scan : simulation study and comparison with plane wave results

The ever-increasing use of composite materials in the industry has resulted in the need for new, intricate approaches to not only properly characterize their anisotropic mechanical properties (i.e., the visco-elastic tensor), but also to detect various types of internal flaws. Both goals can be achieved by the Ultrasonic Polar Scan (UPS). During an UPS experiment, a material spot is insonified at many oblique incidence angles Ψ(θ,φ), with θ the vertical incident angle and φ the inplane polar angle, after which the reflected or transmitted ultrasound signal is recorded. The resulting dataset provides an integral view of the angle-dependent reflection (R) and transmission (T) scatter coefficients, and can be employed to infer the material properties. Although the current UPS scanner provides highly accurate experimental data, it is impractical for in-situ measurements. In order to create a more compact and practical measuring device, we propose the use of a hemispherical phased array, consisting of small piezoelectric elements, to generate a broadband, quasi plane wave signal. It will be shown, based on simulations, that a circular phased array concept allows for the determination of the reflection coefficients in θ − f space, from which the dispersion curves can be immediately inferred. Comparison of these results with the plane wave theoretical results show an excellent agreement

Identification of the elastic properties of isotropic and orthotropic thin-plate materials with the pulsed ultrasonic polar scan

Already in the early 1980's, it has been conjectured that the pulsed ultrasonic polar scan (P-UPS) provides a unique fingerprint of the underlying mechanical elasticity tensor at the insonified material spot. Until now, that premise has not been thoroughly investigated, nor validated, despite the opportunities this would create for NDT and materials science in general. In this paper, we report on the first-ever implementation of an inverse modeling technique on the basis of a genetic optimization scheme in order to extract quantitative information from a P-UPS. We validate the optimization approach for synthetic data, and apply it to experimentally obtained polar scans for annealed aluminum, cold rolled DC-06 steel as well as for carbon fiber reinforced plastics. The investigated samples are plate-like and do not require specific preparation. The inverted material characteristics show good agreement with literature, micro-mechanical models as well as with results obtained through conventional testing procedures