Modeling and Simulation of the Thermoforming Process in Thermoplastic-Matrix Composite Materials

Thermoplastic-matrix composite materials have unique advantages over traditional thermosets including faster processing, improved fracture toughness, and recyclability. These and other benefits have caused increasing interest in the use of these materials in both aerospace and automotive industries. Due to the differences in behavior, these materials require a different type of manufacturing process to thermoset matrix composites. This manufacturing process generally involves using pre manufactured tape-layers. These layers, containing both thermoplastic-matrix and fiber-reinforcement, are aligned to the desired orientation, and stacked up into a “tailored blank” using an automated tape layup machine. They are then heated to the thermoplastic melting temperature in an oven and stamped to shape using a large press. Due to some complex behaviors in processing, however, it is necessary to simulate the forming process prior to manufacturing. Simulation can help to avoid costly trial-anderror type process tuning in order to avoid manufacturing defects like wrinkles and tears and to optimize the use of material. A research effort has been undertaken in order to streamline the process of material characterization toward simulation, which are accomplished using commercially available software. This includes a variety of material characterization tests, as well as forming tests in order to compare simulated results, such as predicted wrinkles and fiber reorientations in complex-shaped parts, to real parts manufactured under the same conditions as the simulations. Finally, a tool has been developed which allows the extension of these forming simulations to inform more accurate structural analyses of as-formed parts

Integration of Material Characterization, Thermoforming Simulation, and As-Formed Structural Analysis for Thermoplastic Composites

An improved simulation-based thermoforming design process based on the integration of material characterization and as-formed structural analysis is proposed. The tendency of thermoplastic composites to wrinkle during forming has made simulation critical to optimized manufacturing, but the material models required are complex and time consuming to create. A suite of experimental methods has been developed for measurement of several required properties of the molten thermoplastic composite. These methods have the potential to enhance thermoplastic composites manufacturing by simplifying and expediting the process. These material properties have been verified by application to thermomechanical forming predictions using commercial simulation software. The forming predictions showed improved agreement with experimental results compared to those using representative material properties. A tool for using thermoforming simulations to inform more accurate structural models has been tested on a simple case study, and produced results that clearly differ from those of models using idealized fiber orientations and thicknesses. This provides evidence that this type of as-formed analysis may be necessary in some cases, and may be further investigated as an open source alternative to commercial analysis software

Measurement of the B0s Lifetime in the Flavor-Specific Decay Channel B0s→D−sμ+νX

We present an updated measurement of the B0s lifetime using the semileptonic decays B0s→D−sμ+νX, with D−s→ϕπ− and ϕ→K+K− (and the charge conjugate process). This measurement uses the full Tevatron Run II sample of proton-antiproton collisions at s√=1.96  TeV, comprising an integrated luminosity of 10.4  fb−1. We find a flavor-specific lifetime τfs(B0s)=1.479±0.010(stat)±0.021(syst)  ps. This technique is also used to determine the B0 lifetime using the analogous B0→D−μ+νX decay with D−→ϕπ− and ϕ→K+K−, yielding τ(B0)=1.534±0.019(stat)±0.021(syst)  ps. Both measurements are consistent with the current world averages, and the B0s lifetime measurement is one of the most precise to date. Taking advantage of the cancellation of systematic uncertainties, we determine the lifetime ratio τfs(B0s)/τ(B0)=0.964±0.013(stat)±0.007(syst)

Search for minimal supergravity in single-electron events with jets and large missing transverse energy in pp-bar collisions at s√=1.8TeV

This is the publisher's version, also available electronically from http://journals.aps.org/prd/abstract/10.1103/PhysRevD.66.112001.We describe a search for evidence of minimal supergravity (MSUGRA) in 92.7pb(-1) of data collected with the DØ detector at the Fermilab Tevatron pp-bar collider at s√=1.8TeV. Events with a single electron, four or more jets, and large missing transverse energy were used in this search. The major backgrounds are from W+jets, misidentified multijet, tt-bar, and WW production. We observe no excess above the expected number of background events in our data. A new limit in terms of MSUGRA model parameters is obtained

Measurement of the top quark mass in the lepton+jets channel using the ideogram method

This is the publisher's version, also available electronically from http://journals.aps.org/prd/abstract/10.1103/PhysRevD.75.092001

Properties of L=1 B(1) and B∗(2) Mesons

This is the publisher's version, also available electronically from http://journals.aps.org/prl/abstract/10.1103/PhysRevLett.99.172001.This Letter presents the first strong evidence for the resolution of the excited B mesons B(1) and B∗(2) as two separate states in fully reconstructed decays to B(+)(*)π−. The mass of B(1) is measured to be 5720.6±2.4±1.4  MeV/c(2) and the mass difference ΔM between B∗(2) and B(1) is 26.2±3.1±0.9  MeV/c(2), giving the mass of the B∗(2) as 5746.8±2.4±1.7  MeV/c(2). The production rate for B(1) and B∗(2) mesons is determined to be a fraction (13.9±1.9±3.2)% of the production rate of the B(+) meson

Lifetime Difference and CP-Violating Phase in the B(0)(s)System

This is the publisher's version, also available electronically from http://journals.aps.org/prl/abstract/10.1103/PhysRevLett.98.121801

Measurement of the angular distribution of electrons from W⃗ eν decays observed in pp-bar collisions at s√=1.8 TeV

This is the publisher's version, also available electronically from http://journals.aps.org/prd/abstract/10.1103/PhysRevD.63.072001.We present the first measurement of the electron angular distribution parameter α(2) in W⃗ eν events produced in proton-antiproton collisions as a function of the W boson transverse momentum. Our analysis is based on data collected using the DØ detector during the 1994–1995 Fermilab Tevatron run. We compare our results with next-to-leading order perturbative QCD, which predicts an angular distribution of (1±α(1c)osθ*+α(2)cos(2)θ*), where θ* is the polar angle of the electron in the Collins-Soper frame. In the presence of QCD corrections, the parameters α(1) and α(2) become functions of pWT, the W boson transverse momentum. This measurement provides a test of next-to-leading order QCD corrections which are a non-negligible contribution to the W boson mass measurement

Search for Decay of a Fermiophobic Higgs Boson h(f)→γγ with the D0 Detector at s√=1.96 TeV

This is the publisher's version, also available electronically from http://journals.aps.org/prl/abstract/10.1103/PhysRevLett.101.051801.We report the results of a search for a narrow resonance decaying into two photons in 1.1  fb(−1) of data collected by the D0 experiment at the Fermilab Tevatron Collider during the period 2002–2006. We find no evidence for such a resonance and set a lower limit on the mass of a fermiophobic Higgs boson of m(hf)>100  GeV at the 95% C.L. This exclusion limit exceeds those obtained in previous searches at the Fermilab Tevatron and covers a significant region of the parameter space B(hf→γγ) vs mhf which was not accessible at the CERN Large Electron-Positron Collider

Study of the Decay B(0)(s)→D(*)(s)D(*)(s)

This is the publisher's version, also available electronically from http://journals.aps.org/prl/abstract/10.1103/PhysRevLett.99.241801