179,924 research outputs found
Joshua Davis: Author of Spare Parts
No full textCitation: K-State First (2016). Joshua Davis: Author of Spare Parts [Flier]. Manhattan, Kansas: K-State First.Flyer advertising Joshua Davis's author talk at Kansas State University
Steven Johnson Author Talk Poster
No full textK-State Book NetworkA poster advertising an author talk by Steven Johnson at Kansas State University on September 3, 2014. Steven Johnson's book "The Ghost Map" was the 2014-2015 common book
A continuous/discontinuous Galerkin formulation for a strain gradient-dependent damage model
No full textThe numerical solution of strain gradient-dependent continuum problems has been hindered by continuity demands on the basis functions. The presence of terms in constitutive models that involve gradients of the strain field means that the continuity of standard finite element shape functions is insufficient. Despite a resurgence of research interest in strain gradient continuum models to represent micro-mechanical effects, a sound, effective and simple framework for the numerical solution of strain gradient-dependent problems is lacking. Here, a formulation is presented which allows the use of finite element shape functions for the solution of a prototype strain gradient-dependent damage model. The formulation is examined in two dimensions for the simulation of crack propagation. Particular attention is paid to the application of non-standard boundary conditions
Temperature and strain scaling laws for the critical current density in Nb(_3)Sn and Nb(_3)Al conductors in high magnetic fields
No full textDetailed, accurate measurements of critical current density and resistivity to determine the upper critical field have been made on a technological NbsAl conductor in magnetic fields up to 15 T, temperatures from 4.2 K up to the critical temperature and in the strain range from -1.8% to 0.7%. The uncertainty in temperature above 4.2 K was equivalent to ± 100 mK with a stability during the measurements of < 5 mK up to a limiting current of 80 A and a typical noise level of 1 µ Vm(^-1).When B(_c2){T,ε) is defined at 5%pn, 50%pn or 95%/%pn, an empirical relation is found where and an approximate relation, holds. The Jε data were parameterised using F(_p) = J(_E)B = A(ε)[Bc(_2)](^n)b(^p)(1-b)(^9) where b = B/B(_c2)(T,ε). When B(_c2)(T,ε) is constrained to be the value at 50%pn or 95%pn, the scaling law for F(_p) breaks down such that p and q are strong functions of temperature and q is also a strong function of strain. However, when B(_c2)(T,ε) is defined at 5%pn, there is good scaling where p and q are constants independent of temperature and strain. F(_p) can also be approximated by a Kramer form where the Ginzburg-Landau constant is γ is the electronic density of states and is interpreted as the average B(_c2) for the bulk where percolative current flow occurs. The critical current density of Hot Isostatic Pressed (HIP'ed) and unHIP'ed Nb(_3)Sn Modified Jelly Roll wires has also been measured at 4.2 K. The critical current and upper critical field were decreased for the HIP'ed sample. The reduced upper critical field of the HIP'ed wire was found to be less sensitive to strain than the unHIP'ed wire. The exponent of B(_c2) in the flux pinning scaling law increased from 0.86 to 2.14 as a result of the HIP processing
Intermediate strain rate testing methodologies and full-field optical strain measurement techniques for composite materials characterisation
No full textTwo optical full-field strain measurement techniques, Digital Image Correlation and the Grid Method, are applied to characterise the strain-rate dependent constitutive behaviour of composite materials. Optical strain measurement techniques based on full-field images are well established for material characterisation in the quasi-static strain rate region, however in this work they are developed to study the material behaviour at intermediate strain rates, which is relatively unexplored. For this purpose a testing methodology that combines high speed imaging and the use of a high speed test machine is devised. The overall goal is to extract composite materials constitutive parameters to be used in the modelling of strain rate dependent behaviour. Particularly the strain rate dependence of the stiffness of glass and carbon fibre reinforced epoxy materials is investigated. A characterisation procedure based on off-axis specimens with oblique end-tabs is developed and applied to the study of the shear behaviour of a carbon/epoxy composite material.The research in the PhD programme constitutes an essential first step for more profitable applications of full-field measurement techniques to high speed testing. Full-field data acquired with the experimental methodology devised here can be used to investigate non linear material behaviours. Furthermore this experimental methodology, applied to specimens that generate non uniform strain fields, can produce strain maps useful for the application of the Virtual Fields Method. This will lead to a reduction of the experiments needed to characterise materials
Epidermal Passive RFID Strain Sensor for Assisted Technologies
No full textAn epidermal passive wireless strain sensor using RFID tags is presented. The tag is intended to detect eyebrow or neck skin stretch where paraplegic patients have the capability to tweak facial muscles. The tag is designed on a Barium Titanate loaded PDMS substrate and is assessed to demonstrate the strain gauge sensitivity and repeatability as a function of skin stretch
Discontinuous modelling of strain localisation and failure
No full textThe computational simulation of failure in solids poses many challenges. A proper understanding of how structures respond under loading, both before and past the peak load, is important for safe and economical constructions. This requires numerical models for failure which are both faithful to the physical reality and mathematically well founded. A serious computational issue is that of objectivity with respect to the spatial discretisation of a problem. This requires that upon refinement of the spatial discretisation of a problem, a unique, physically meaningful result is approached. One approach to ensure objectivity with respect to spatial discretisation when simulating failure in solids is to allow displacement discontinuities in the solution. In this work, different techniques, of varying complexity, are developed to simulate displacement discontinuities which are independent of the spatial discretisation using finite elements. The different techniques are then critically evaluated. The first model examined involves adding only the effect of a displacement discontinuity to a finite element as an incompatible strain mode. This allows a traction–separation relationship to be applied at an interface and can be implemented simply in a standard finite element code. It is however shown that this type of model can be cast in an equivalent continuum format, a form which is known to be sensitive to the spatial discretisation. The second approach developed involves the addition of the Heaviside function to the underlying finite element interpolation basis. This method is based on the partition of unity concept, and allows the Heaviside function to be added locally to a finite element mesh to simulate a propagating displacement discontinuity. The approach is formulated for geometrically linear, geometrically nonlinear, quasi-static and dynamic problems. It is shown to be completely independent of the spatial discretisation. The partition of unity-based model is used also to simulate failure using a regularised strain softening model. When a critical level of inelastic deformation is reached, a displacement discontinuity is inserted. This model is better suited to modelling the entire failure process than a continuum or discontinuous model alone. Through numerical examples, it is shown that the inclusion of a displacement discontinuity during the failure process can lead to a different failure mode than for a continuum-only model
On-line monitoring of multi-component strain development in a tufting needle using optical fibre Bragg grating sensors
No full textDynamic loadings induced on a tufting needle during the tufting of dry carbon fibre preform via a commercial robot-controlled tufting head were investigated in situ and in real-time using optical fibre Bragg grating (FBG) sensors bonded to the needle shaft. The sensors were configured such that the axial strain and bending moments experienced by the needle could be measured. A study of the influence of thread and thread type on the strain imparted to the needle revealed axial strain profiles which had equivalent trends but different magnitudes. The mean of the maximum axial compression strains measured during the tufting of a 4-ply quasi-isotropic carbon fibre dry preform were - 499 ± 79 με, - 463 ± 51 με and - 431 ± 59 με for a needle without thread, with metal wire and with Kevlar® thread, respectively. The needle similarly exhibited bending moments of different magnitude when the different needle feeding configurations were used
Evaluation of a high spatial resolution temperature compensated distributed strain sensor using a temperature controlled strain rig
No full textWe demonstrate a scheme which allows for temperature corrected distributed strain measurements under environments involving simultaneous application of strain and temperature, with enhanced spatial (5 cms), strain (66 µ.epsilon) and temperature resolutions (1.9°C). The technique utilizes the combination of frequency based BOCDA with Brillouin intensity measurements
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