bluuebunny/crossref_metadata_2025_split huggingface dataset:
A MEMS Structure for Measuring the Fracture Strength of Thin Films
Authors: Johnson George C. , Jones Peter T. , Howe Roger T. , Au Michael 
Published: January 2022

Abstract
A surface micromachined structure for measuring the fracture strength of thin films used in MEMS has been developed [1.2]. The test structure consists of a rigid central shuttle which is suspended above the substrate by folded flexures. Extending from the shuttle are six cantilever beams of varying lengths. As the shuttle is pushed by an off-chip probe, the beams hit contact pads, which are attached to the substrate, and bend until they break. A vernier gauge inside the central shuttle allows measurement of the displacement to within 0.2μm. Optical micrographs of the fracture test structure and of a single bending beam are shown in Figure 1.
In-Situ Test Structures for Metrological and Mechanical Characterization of MEMS
Authors: Gupta Raj K. 
Published: January 2022

Abstract
Separating geometrical dependence from extracted mechanical stiffness parameters to obtain fundamental mechanical properties, such as the Young’s Modulus E and the internal (residual) stress σ within 10%, is difficult. Mechanical stiffness, obtained from an intermediate measured quantity, generally depends on high powers of structural geometry, but only linearly with mechanical property. For example, the maximum deflection of a uniformly loaded beam under linear-elastic conditions is proportional to L4 and 1/t3, where L is the beam length and t is the thickness, but is only linearly proportional to E. Secondly, geometric measurements to sub-micron precision as required for microelectromechanical systems (MEMS) require error-free techniques and metrological calibration standards. In this talk, methods for error-reduction, using techniques for detecting errors in measured geometry and a proposed method for in-situ wafer-level electrical measurement of geometry, are presented.
Asymptotic Crack-Tip Fields in an Anisotropic Plate Subjected to Bending Moments and Transverse Shear Loads
Authors: Yuan F. G. , Yang S. 
Published: January 2022

Abstract
Asymptotic crack-tip fields in an anisotropic plate under bending moments and transverse shear loads including the effect of transverse shear deformation is presented. Utilizing the Reissner variational principle, the equilibrium equations and stress resultant-displacement relations are obtained. Assuming the displacement and stress resultant are in a separation of variable form, it is found that the equations governing crack-tip fields of an anisotropic plate bending are analogous to those governing generalized plane deformation of a composite. Thus the Stroh formalism can be used to characterize the crack-tip fields of the anisotropic plate and the energy release rate can be expressed in a real form in terms of stress intensity factors. The degenerated case of isotropic plates is also presented. Finally, the coefficients of the asymptotic expansion can be obtained from the J-integral method and Betti’s reciprocal theorem together with the auxiliary fields.
A Novel Compatibility/ Equilibrium Based Iterative Post-Processing Approach for Axisymmetric Brittle Matrix Composites
Authors: Chaudhuri R. A. , Pagano N. J. , Tandon G. P. , Khan A. H. 
Published: January 2022

Abstract
A semi-analytical iterative approach for enhancing the existing two-dimensional quasi-continuous axisymmetric stress field for a brittle matrix micro-composite (e.g., a single fiber surrounded by a concentric matrix cylinder), is presented. The existing solution due to Pagano employs Reissner’s variational theorem in conjunction with an equilibrium stress field in which the radial (r-) dependence is assumed a priori.
In the present approach, the stress distribution in the radial direction obtained from the afore-cited variational model is improved a posteriori through an iterative approach that involves successive substitution of the previously computed strains (or stresses) into the equations of compatibility and equilibrium. The equations of compatibility are selected such that they form Euler equations corresponding to an appropriate variational principle, such as the principle of minimum complementary potential energy, etc.
The boundary/interface conditions at r = constant and z = constant surfaces/interfaces are satisfied in the pointwise sense. The expressions for the improved axisymmetric displacement and stress fields are derived using the symbolic language, MAPLE. An illustrative thermal stress problem is currently being solved, and will be used to compare with the existing variational solution.
Influence of Multiple Fiber Breaks on Stresses in a Fiber Composite With a Creeping Matrix
Authors: Beyerlein Irene J. 
Published: January 2022

Abstract
In this work, the influence of pre-existing fiber breaks on the local creep response of a planar unidirectional fiber composite under steady axial tension is investigated. Shear deformation of the Newtonian viscous matrix material or interface is assumed to dominate the creep response and result in time and temperature induced fiber failures. The recently developed computational mechanics technique, called viscous break interaction (VBI), is used to compute the time-dependent stress and strain redistributions in the fibers and matrix in response to large numbers of transversely aligned and staggered fiber breaks. In VBI, the key influence function in response to one fiber break is built on shear-lag theory, and when employing weighted superposition concepts to this function, the stress fields around multiple breaks is then calculated. The results uncover distinctions in the stress redistribution between large numbers of aligned breaks, e. g. transverse cracks and a finite and infinite periodic row of short cracks, versus a large process zone of staggered (misaligned) breaks. The results also show how both the time growing interactions and spatial arrangement and size of several close breaks influence local matrix creep rate, fiber tensile stress redistribution, and macroscopically, the timescales of multiple creep stages in overall composite strain. In the present application of the VBI technique, the composite model is representative of polymer matrix composites and also ceramic composites with a viscous secondary phase at elevated temperatures. For these systems, the model assumes the reinforcement is the primary load bearing component with time-independent, elastic properties and has a much higher volume fraction than that of the matrix. These studies on the time evolution of local stress are important for modeling the statistical evolution of process zone or crack-tip failure mechanisms in time.
Damage Mechanics for Hybrid Laminates
Authors: Whitcomb John , Noh Jae , Srirengan Kanthikannan 
Published: January 2022

Abstract
Damage in composite materials accumulates in a diffuse manner. Accounting for this damage in a progressive failure analysis requires an accurate measure of the degraded stiffness coefficients. This paper describes micromechanics models for predicting the effect of distributed cracks on the engineering properties (extensional and shear moduli, Poisson’s ratios, and thermal expansion coefficients). The configuration is shown schematically in Figure 1. The unit cell consists of three laminae: a cracked central lamina and two adjacent laminae. The adjacent laminae may or may not be damaged.
The effective properties of a cracked lamina are affected by the presence of the adjacent laminae. However, in an earlier paper by the authors (Reference. 1), it was shown that the effective properties of a cracked lamina normalized by their original values were quite insensitive to the adjacent lamina orientation and even the material system of the laminae group. This is illustrated in Figure 2. The results in Reference 1 were for a single cracked lamina, the adjacent lamina had the same orientation, and all three laminae had the same undamaged unidirectional properties. Also, in calculating the effective engineering moduli, shear-extension coupling terms were ignored. The current effort builds on the results in Reference 1. This paper considers hybrid laminates, adjacent plies with different orientations, damage in single and multiple laminae, a wider range of material systems, and thermal expansion coefficients. Quantitative measures are presented for the errors introduced when shear-extension coupling terms are ignored. Reference 1 used fully three-dimensional finite element models. This paper discusses the use of much more efficient quasi-3D models.
An Approach for Thermoviscoelastic Micro-Analysis for Woven Fabric Laminates
Authors: Chung Peter W. , Tamma Kumar K. 
Published: January 2022

Abstract
Structures containing micromechanical details is an active area of interest in the analysis of composite materials. The present investigation proposes a method for studying the thermorheological-viscoelastic problem associated with manufacturing and post-analysis of woven fabric laminates. The homogenization approach is employed to resolve the multi-scale issue. A general purpose 3-D finite element code has been developed containing features for heterogeneous thermoviscoelastic constituents exhibiting thermorheological behavior. Material nonlinearities via temperature dependent properties with instantaneous memory are considered and thus, allow for prediction of curing and cool-down residual stresses during manufacture. Test examples and comparisons with experimental observations are also presented.
Nonlinear Dynamic Snap-Through Buckling of Composite Laminated Spherical Shells
Authors: Yiqian Yang , Duan Zhang , Hongye Zhou , Hezhong Ma , Tsunkuei Wang 
Published: January 2022

Abstract
In this paper, a general, strain-consistent, third-order displacement field of shells is proposed. On this basis, the nonlinear theory of composite laminated shells including third-order transverse shear deformation and rotary inertia is developed. Hamilton’s variational principle is used to derive the nonlinear static and dynamic governing differential equations and the corresponding boundary conditions of composite laminated anisotropic general shells under the orthogonal curvilinear coordinates. And the form of spherical shells is degenerated. The model accounts for the cubic variations of the in-plane displacements through the thickness (thus, does not require any shear correction coefficients), stretching of transverse normals, the von karman nonlinear strain-displacement relations, initial geometric imperfection, rotary inertia, elastic foundations and viscous damping in order to simulate the real structures. The corresponding constitutive equations of composite laminated shells are derived. This paper uses the global orthogonal interior collocation method in space domain and the unconditionally stable Newmark-Beta and Houbolt numerical integration schemes in time domain to comprehensively investigate dynamic axisymmetric behavior of laminated cylindrically orthotropic composite shallow spherical shells subjected to suddenly applied loads. The sufficient condition for dynamic buckling, from the energy transfer consideration, is defined as the smallest load for which an unbounded motion is initiated at one generalized displacement, and the pressure corresponding to a sudden jump in the maximum volume change in the time history of the shell structure is taken as dynamic buckling pressure herein. For the sake of comparison, the results of first-order transverse shear and classical shell theories are presented in this paper. Results of detailed parametric imperfection, the total number of layers, lamination schemes, viscous damping, loading type and loading duration, the loaded area, loading rates, Winkler-Pasternak elastic foundations, opening semi-angle of circular hole, aritifical viscosity of difference scheme, boundary conditions, rotary inertia, transverse shear deformation, h/R (thickness/radius ratio of shells) and dynamic buckling criterion on the buckling loads. Previously the researches on shallow spherical shells were based on shallow shell assumptions. But in this paper, these assumptions are abandoned, thus the theoretical model can be used to study shallow spherical shells, as well as hemi-spherical shells and complete spherical shells. The semi-analytical solutions offered by this paper will provide bench-mark numerical results to test the accuracy of numerical methods. This paper clears up the confused ideas about the different effects of transverse shear deformation on the shallow and deep spherical shells in references.
Moiré Interferometry Measurements of Interlaminar Deformation at an Open Hole in Laminated Composite Materials
Authors: Mollenhauer David , Post Daniel , Reifsnider Kenneth 
Published: January 2022

Abstract
The deformation on cylindrical surfaces of holes in tensile-loaded laminated composite specimens was measured using new moiré interferometry techniques. Two composite tensile specimens, fabricated from IM7/5250-4 pre-preg with ply layups of [0°4/90°4]3s and [+30°2/-30°2/90°4]3s, were examined using the newly developed moiré interferometry techniques. Circumferential and thickness direction displacement fringe patterns (each 3° wide) were assembled into 90°-wide mosaics around the hole periphery for both composite specimens. Distributions of strain were calculated with high confidence on a sub-ply basis at select angular locations. Measured strain behavior was complex and displayed ply-by-ply treands. Large ply-related variations in the circumferential strain were observed at certain angular locations around the periphery of the holes in both composites. Extremely large ply-by-ply variations of the shear strain were also documented in both composites. Peak values of shear strain approached 30 times the applied far-field axial strain. Post-loaded viscoelastic shearing strains were recorded that were associated with the regions of large load-induced shearing strains. Large ply-group related variations in the thickness direction strain were observed in the [+30°2/-30°2/90°4]3s specimen. An important large-scale trend was observed where the thickness direction strain tended to be more tensile near the outside faces of the laminate than near the mid-ply region. The measured strains were compared with the three-dimensional analysis technique known as Spline Variational Elastic Laminate Technology (SVELT), resulting in a very close match and corroborating the usefulness of SVELT.
Influence of Adhesive Reinforcement on the Mode I Fracture Toughness of a Bonded Joint
Authors: Forte M. S. , Whitney J. M. , Schoeppner G. A. 
Published: January 2022

Abstract
The influence of adhesive reinforcement on the fracture toughness is investigated with a computer model based on a variational theorem that has been shown to accurately predict stress fields and energy release rates for cracked laminates. An axisymmetric damage plane strain model was developed and used to determine the Mode I energy release rate for midplane cracking in aluminum bonded specimens with varying amounts adhesive reinforcement. The calculated energy release rates are compared to closed form analyses in a systematic test program.
An Investigation of the Effects of Layer Thickness on the Fracture Behavior of Layered NiAl/V Composites
Authors: Li M. , Wang R. , Katsube N. , Soboyejo W. O. 
Published: January 2022

Abstract
The effect of vanadium layer thickness (100, 200 and 400 μm) on the resistance curve behavior of NiAl/V microlaminates are examined in this paper. The fracture resistance of the NiAl/V microlaminates is shown to increase with increasing layer thickness. The improved fracture toughness (compared to that of unreinforced NiAl) is associated with crack bridging and the interactions of cracks with vanadium layers. The re-initiation of cracks in adjacent NiAl layers is modeled using finite element methods. The re-initiation is shown to occur as a result of strain concentrations at the interface between the adjacent NiAl layers and vanadium layers. The initial deviation of the re-initiated cracks from the pure mode I direction is shown to occur in the direction of maximum shear strain. Toughening due to crack bridging is also modeled using finite element models of the observed crack/microstructure profiles.
Behavior of Polymeric Composites Exposed to a Heat Flux Simulating Fire
Authors: Potocki Mark L. , Tuttle Mark E. , Mescher Ann M. 
Published: January 2022

Abstract
An analytical procedure is presented which can be used to model the behavior of a polymeric composite panel when subjected to both external loading as well as the high heat flux associated with a fire. The procedure accounts for the elastic and viscoelastic-viscoplastic response, thermal gradients and thermal stresses, and pyrolysis effects. Predictions based on estimated properties for an E-glass/polyester composite panel subjected to a uniaxial tensile load of 250 kN/m (1430 lb/in) and a 1-D heat flux of 10 kW/m2 (22 BTU/hr/in2) are presented. The predicted response is considered to be a reasonable representation of the expected behavior.
Preference of grade and lymphovascular invasion over invasive size measurement in stage I lung adenocarcinoma
Authors: Itami Hiroe , Kawaguchi Takeshi , Yoshikawa Daiki , Watanabe Takashi , Terada Chiyoko , Okada Fumi , Uchiyama Tomoko , Takeda Maiko , Ishida Eiwa , Nishimoto Yuko , Okada Hiroshi , Kushibe Keiji , Sawabata Noriyoshi , Ohbayashi Chiho 
Published: January 2022

AimsAlthough it is necessary to measure the invasive size of lung adenocarcinoma with a lepidic component, it is not uncommon to have trouble in measuring the invasive size of lung adenocarcinoma. This study examined whether there were other stronger prognostic factors than invasive size.MethodsWe characterised the clinicopathological features associated with recurrence-free survival (RFS) of 686 patients with the pathological stage (p-Stage) I lung adenocarcinoma. Moreover, we compared the area under the curve (AUC) values for recurrence between various combinations of pathological-baseline (age & sex & p-Stage based on invasive size) (B(i)) and several prognostic factors, and various combinations of p-baseline based on total tumour size (B(t)) and several prognostic factors.ResultsAUC showed no significant differences between B(i) & new International Association for the Study of Lung Cancer grade (G) or vascular invasion (V), and B(t) & G or V. AUC was the highest in B & G & lymphatic invasion (L) & V. RFS was significantly shorter in patients with G3 OR L(+) OR V(+) than in those with G≤2 AND L(-) AND V(-) in each p-Stage based on invasive size (p-Stage(i)) and p-Stage based on total tumour size (p-Stage(t)) (p<0.05), and there were no significant differences in RFS between each p-Stage(i) and p-Stage(t).ConclusionsIn any invasive size or total tumour size of p-Stage I lung adenocarcinoma, G, L and V are more powerful prognostic factors than the size criteria of p-Stage. Therefore, pathologists should focus on these pathological findings.
Laterality of previous stoke affects endovascular thrombectomy outcomes
Authors: Bageac Devin V , Gershon Blake S , Chada Deeksha , Siddiqui Neha , Majidi Shahram , Fifi Johanna T , De Leacy Reade 
Published: January 2022

BackgroundInvestigations into the effect of previous stroke on thrombectomy outcomes have yielded conflicting results, and are limited by small sample sizes. We present the results of a large single center retrospective study aimed at investigating the effect of chronic stroke laterality on thrombectomy outcomes.MethodsA prospectively maintained database was queried for all thrombectomy cases conducted between December 2014 and January 2020, and patient imaging was prospectively reviewed for evidence of prior supratentorial infarction. Procedural, clinical, and demographic characteristics were recorded, and good clinical outcome was defined as a 90 day modified Rankin Scale (mRS) score of <2 or mRS score unchanged if baseline was >2.ResultsThe final analysis cohort included 555 patients, 79 of whom were found to have radiographic evidence of prior chronic infarcts. On univariate analysis, patients with any chronic supratentorial infarct achieved a lower rate of good clinical outcome than patients with no chronic infarct (22.8% vs 41.0%, p=0.0021). With regard to subgroups, this difference remained only in patients with ipsilateral (14.3%, p=0.0018) and bilateral (11.8%, p=0.015) lesions. Patients with chronic contralateral supratentorial infarcts were no less likely to achieve good outcomes (40.7%, p=0.98). After multivariate regression controlling for age, sex, and baseline mRS, chronic ipsilateral infarcts (OR 0.22, CI 0.07 to 0.67) and chronic bilateral infarcts (OR 0.19, CI 0.04 to 0.85) were the only independent predictors of poor outcome in endovascular thrombectomy patients.ConclusionsIn this single center retrospective study of thrombectomy patients with chronic supratentorial infarcts, the laterality of the previous stroke significantly affected the likelihood of good clinical outcomes.
Impact of leukoaraiosis in patients with acute ischemic stroke treated with thrombectomy: a post hoc analysis of the DIRECT-MT trial
Authors: Yi Tingyu , Zhang Yongxin , Chen Wen-huo , Wu Yan-min , Lin Ding-lai , Lin Xiao-hui , Zhang Lei , Xing Peng-fei , Li Tianxiao , Zhang Yongwei , Wang Shouchun , Yang Pengfei , Cai Ming-zhi , Liu Jianmin 
Published: January 2022

BackgroundThe influence of leukoaraiosis in patients with acute ischemic stroke (AIS) given intra-arterial treatment (IAT) with or without preceding intravenous thrombolysis (IVT) remains unknown.ObjectiveTo assess the clinical and radiological outcomes of IAT in patients with or without leukoaraiosis.MethodsPatients of the direct mechanical thrombectomy trial (DIRECT-MT) whose leukoaraiosis grade could be assessed were included. DIRECT-MT was a randomized clinical trial performed in China to assess the effect of direct IAT compared with intravenous thrombolysis plus IAT. We employed the Age-Related White Matter Changes Scale for grading leukoaraiosis (ARWMC, 0 indicates no leukoaraiosis, 1–2 indicates mild-to-moderate leukoaraiosis, and 3 indicates severe leukoaraiosis) based on brain CT. The primary outcome was the score on the modified Rankin Scale (mRS) assessed at 90 days.ResultsThere were 656 patients in the trial, 649 patients who were included, with 432 patients without leukoaraiosis, and 217 (33.4%) patients with leukoaraiosis divided into mild-to-moderate (n=139) and severe groups (n=78). Leukoaraiosis was a predictor of a worse mRS score (adjusted OR (aOR)=0.7 (95% CI 0.5 to 0.8)) and higher mortality (aOR=1.4 (1.1 to 1.9)), but it was not associated with symptomatic intracranial hemorrhage (sICH) (aOR=0.9 (0.5 to 1.5)). IVT preceding IAT did not increase sICH risk for patients with no (aOR=1.4 (0.6 to 3.4)), mild-to-moderate (aOR=1.5 (0.3 to 7.8)), or severe (aOR=1.5 (0.1 to 21.3)) leukoaraiosis.ConclusionPatients with leukoaraiosis with AIS due to large vessel occlusion are at increased risk of a poor functional outcome after IAT but demonstrate similar sICH rates, and IVT preceding IAT does not increase the risk of sICH in Chinese patients with leukoaraiosis.