bluuebunny/crossref_metadata_2025 huggingface dataset:
An Explicit Finite Element Study of Shear Localization During Orthogonal Cutting Process
Authors: Scott De-Shin Liu , Hong Jack
Published: March 2022

The shear localization phenomena during serrated chip formation in high speed orthogonal metal cutting process have been studied by using the explicit finite element analysis. A three dimensional computational model has been developed for analyzing dynamic thermomechanical deformations of a thermally softening viscoplastic workpiece material subjected to various tool cutting speeds and tool rake angles. The shear band characteristics such as temperature contour, effective plastic strain, effective plastic strain rate, propagating speed and orientation are investigated for each cases. Cutting forces can be estimated by this 3D model. The predictions of the finite element analysis are shown that above a critical high cutting speeds the secondary shear of the chip on rake surface appear to be a negligible effect which indicated the chip segments can be separate completely due to extensive shear in the primary shear zone; this phenomena agreed well with the experimental observations. The numerical model presented here can easily applied to study the oblique cutting process.
The Effect of Thermomechanical Strain Cycling on the Fatigue Life of Gas Turbine Material In-738LC: A Life Prediction Model
Authors: Zamrik Sam Y. , Renauld Mark L.
Published: March 2022

Experimental and analytical method is developed to address the effect of thermomechanical fatigue (TMF) on a nickel base superalloy which is a γ’/ (Ni3Al) strengthened material used primarily for land based gas turbine blading. A life prediction model is developed on the basis of a tensile hysteresis energy approach which incorporates the effect of creep, environment, and temperature. The developed life prediction model has shown a good predictive capability to correlate most of IN-738 out-of-phase TMF data from numerous researchers into a 3x scatterband. The TMF tests were carried out on two sets of cyclic temperatures of 482–816°C (900–1500°F) and 482–871°C (900–1600°F). In addition, isothermal tests were carried out at 816°C (1500°F) under strain ranges from 0.3% to 0.8% for life comparison between isothermal and TMF. The results show that the TMF out-of-phase type cycle is the most damaging cycle for the IN-738LC material when compared to both in-phase and isothermal cycles. All experiments were strain-controlled with a triangular waveform and an A-ratio (A = εamp/εmean) = ∞.
Scientific Implications in High Peak Power Nd:YAG Laser Material Removal of Al-30%SiC Composite
Authors: Nagarathnam K. , Chen X. , Mazumder J.
Published: March 2022

This paper outlines the scientific implications of a high peak power, high beam quality Nd:YAG laser in manufacturing applications and discusses the significance of optimizing key laser process parameters in material removal characteristics of a Al-30% SiC composite. The potential applications of this emerging technology are primarily targeted towards advanced components fabrication in industries such as aeronautic, space, power generation, and automotive. Some of the unique advantages include better beam characteristics such as focusability, improved dimensional accuracy and tolerance, higher production rates, process maneuverability using suitable lens and fiber optic beam delivery systems, and elimination of mechanical tool wear in comparison to the traditional drilling techniques. Percussion drilling experiments were performed in two batches on 12.5 mm thick plates of Al-30% by volume of SiC composite material. The laser consists of a cw-pumped Nd:YAG oscillator followed by a cw face-pumped, total internal reflection Nd:YAG slab for the amplifier gain medium, a master-oscillator-power-amplifier (MOPA) configuration. Both the second harmonic wavelength (532 nm) and the fundamental wavelength (1064 nm) were used, with average powers ranging from 35 W to 90 W. Two pulse formats were employed: Q-switched or simultaneously modelocked and Q-switched. A concentric nozzle was used with O2 assist gas at 45 psig pressure at the regulator. The holes were produced both normal to and 45° angle to the surface. Based on the measured geometrical data, circularity and dross ratios have been proposed and correlated with the process variables. The absence of cracking was evident from the transverse cross-sections of the produced holes. Results of the microstructural aspects such as the morphology and concentration of alloying elements in the matrix and second phase constituents of the unaffected substrate and the nearby regions of the laser drilled holes provided encouraging evidence for the retention of similar morphology, minimal heat affected zone, and little or no recast layer, under select process conditions. The findings in this present study emphasize the uniqueness of this modern laser material removal technique as an advanced manufacturing tool with broader future potential.
A Robust Design Methodology for Structural Control Using Piezoelectric Materials
Authors: Sunar M. , Hyder S. J. , Kahraman R.
Published: March 2022

Piezoelectric materials are modelled using finite element method. Steady thermal effects are included in the model. The model is used in piezoelectric control of flexible structures. The robustness of a piezoelectric control system consisting of a master structure and a pair of piezoelectric actuators is considered by the use of Taguchi methodology. The effects of the location, thickness and width of the actuators are investigated on the control performance of the system subjected to mechanical and steady thermal disturbances. Based on the numerical results it is concluded that the width of the actuators has the most profound effect on the control performance.
Passive Control of Multi-Jointed Structures
Authors: Ettouney Mohammed M. , Daddazio Raymond P. , Abboud Najib N.
Published: March 2022

Reducing the amplitude of structural response generated by noise sources such as machine vibrations using passive control measures is of interest to design engineers. This study will focus on the role of joints in multi-jointed structures in the passive control of structural response.

In a multi-jointed structure, joints play a major role in the response of the structure. First, joints regulate the equilibrium of the whole structure. In such a role, they can act, for example, to transform a pure axial wave in a horizontal member in the structure into a pure flexural wave in a vertical member connected to it at a joint. Second, they are the “recipients” of the noise sources from the secondary beams and floors of the structure. In such a role, joints act as a filter between the noise source and the rest of the structure. These two roles point to the possibility of modifying joints so as to passively control the response of a multi-jointed structure.

In this study, the addition of energy loss mechanisms, which are concentrated at the joints is evaluated. These energy loss mechanisms include adding filler materials with high loss factor. The different parameters affecting the structural response will be evaluated. These parameters include the amount of added material to the joints, relative loss factors of both structure and the added material and the degree of reductions in structural responses. In all the cases studied, a consideration of the practical engineering detailing of such systems will be discussed.
Nonlinear Oscillations of Circular Plates Near Critical Speed
Authors: Raman Arvind , Mote C. D.
Published: March 2022

The nonlinear response of an axisymmetric, thin elastic circular plate subject to a constant, space-fixed transverse force and rotating near a critical speed of an asymmetric mode, is analyzed. A small-stretch, moderate-rotation plate theory of Nowinski (1964), leading to von Kármán type field equations is used. This leads to nonlinear modal interactions of a pair of 1 – 1 internally resonant, asymmetric modes which are studied through first-order averaging. The resulting amplitude equations represent a system whose O(2) symmetry is broken by a resonant rotating force.

The nonlinear coupling of the modes induces steady state solutions that have no apparent evolution from any previous linear analyses of this problem. For undamped disks, the analysis of the averaged Hamiltonian predicts codimension-two bifurcations that give rise to sets of doubly-degenerate, one-dimensional manifolds of steady mixed wave motions. These manifolds of steady motions are bounded in phase space by either mode localized backward travelling wave branches or forward travelling wave branches. On the addition of the smallest damping, the branches of the backward travelling waves with equal modal content become isolated, and numerical investigations indicate the absence of any other types of steady motions.
Load Interaction Effects in Coupon Fatigue Tests Using a Railroad Tank Car Spectrum
Authors: McKeighan Peter C. , Smith Keith B. , Cardinal Joseph W.
Published: March 2022

The loaded vertical coupler force (LVCF) spectrum derived from an instrumented tank car and recorded from over-the-road service conditions is dominated by relatively small loads and also contains high peak loads. The focus of this work was to determine the extent to which the smaller loads in the spectrum can be truncated without adversely impacting crack growth behavior. The influence of clipping, or not achieving the peak tensile and compressive loads, was also investigated as well as the effect of the value used to scale the load spectrum into a stress sequence.

The truncation studies performed at two spectrum scale factors suggest that the two lowest stress levels in the spectrum (approximately 4–5 ksi full range stress level) can be omitted with little measurable effect on spectrum crack growth behavior. Furthermore, tensile and compressive peak load clipping of approximately 25 percent was observed to have little influence on spectrum crack growth behavior. Finally, under certain conditions, the coupon test data compared favorably to calculations utilizing a linear damage, unretarded and interaction-free analytical crack growth prediction model.
Rail Vehicle Dynamic Parameter Identification
Authors: Wilson N. G. , Urban C. L. , Burnett M. S.
Published: March 2022

A cost-effective method of experimentally determining rail vehicle dynamic parameters for use in analytical dynamic models has been developed by the Association of American Railroads (AAR). In this method, the rail vehicle’s rigid body modes of vibration are manually excited and the corresponding resonant frequencies are measured. Using these frequencies, the equations of motion for the system are solved for the vehicle’s mass moments of inertias, center of gravity location, and suspension stiffness. This method of dynamic parameter identification was developed at AAR’s Transportation Technology Center, Pueblo, Colorado.

Compared to competing experimental methods, the AAR method offers the advantage of cost-effectiveness; it requires no expensive equipment and can be executed at remote locations.

This paper describes the AAR method for rail vehicle parameter identification. An example of its use in the characterization of an iron ore rail vehicle is presented. In addition, dynamic simulation results for a transit vehicle, characterized using the AAR method, are compared to track test data for validation.
Condensation Enhancement on a Pool Surface Caused by a Submerged Liquid Jet
Authors: Shumway Rex W.
Published: March 2022

One advanced nuclear reactor design has a residual heat removal (RHR) pipe connected to the bottom of a steam generator outlet plenum. The water in the plenum can become thermally stratified during postulated loss of coolant accidents. Cold water injected through the RHR pipe has the potential effect of increasing the steam condensation on the pool surface due to the stirring action of the jet. The amount of increase depends on a number of factors, including the jet velocity and the pool height above the jet injection point. Prediction of steam condensation rates, before and after the jet breaks the pool surface, is the topic of this paper. Data and correlations exist for pre surface breakthrough and a method has been developed for post breakthrough. The models have been incorporated into the reactor safety analysis computer software known as RELAP5 (1995). Comparisons of predictions against data are presented.
Features of the Calculational Method at Fluid Flow Modelling
Authors: Černe Gregor , Petelin Stojan
Published: March 2022

The ADI (Alternating Direction Implicit) method is used for solving second order partial differential equations. In this case it is applied for viscid incompressible fluid flow described by the Navier-Stokes equation. The method is tested on the simple case of the abrupt area change for the several Reynolds numbers up to Re = 800. A vortex is formed already at low Reynolds number. It affects the pressure field and contribute to the phenomena complicity. The influence of the boundary conditions and nodalization density is also examined.
Bubbly Flow Identification Using Particle Image Velocimetry
Authors: Hassan Y. A. , Schmidl William , Ortiz-Villafuerte J.
Published: March 2022

The shape of a rising air bubble in a pipe flow is investigated with the Particle Image Velocimetry (PIV) flow visualization technique. To do so, a test volume of bubbly flow is globally illuminated with a pulsed light from a continuous wave laser with an acoustic-optic beam chopper, and is observed with four CCD cameras connected to frame grabbers. A digital image of the rising bubble is acquired and analyzed to identify its shape.

A reconstruction method, based on the Dynamic Generalized Hough Transform (DGHT), is described that can determine the two-dimensional shape of a bubble from a PIV image.
Optimization of the Compression (Injection/Compression) Molding Process Using Numerical Simulation
Authors: Davis Bruce A. , Theriault Richard P. , Osswald Tim A.
Published: March 2022

The increasing requirements on auto makers to reduce both the cost and weight of passenger vehicles as well as meet ever more restrictive government regulations make the use of fiber reinforced plastics very attractive. In particular, the use of thermoset composites, such as SMC and BMC, have been used for years by the major auto makers to produce high quality, strong, stiff, and lightweight body panels. Increasingly, it is being used for more structural components throughout the vehicle. However, the use of fiber filled thermoset composites is not limited to the automotive industry. It is also extensively used in electronic components, sports equipment, and general consumer goods. Accordingly, the need to be able to design these molded parts and to predict the complex behavior during manufacture and in service is paramount to reducing the time from concept to production.

This paper introduces a finite element based simulation program that allows the entire molding process, including mold filling, fiber orientation, heat transfer, cure, residual stress and warpage, to be simulated on the computer rather than by experimental prototyping. The software allows designers and engineers to determine product performance during the design stage before the tooling needs to be manufactured. Then, by modifying the design and process with the computer, part optimization can be accomplished prior to building the mold.

The paper discusses the models and methods implemented by the simulation program along with the accompanying assumptions. The results of the simulation are compared with experimental results for a variety of parts. This paper then highlights a case study of an injection/compression molded component showing how the simulation can be used as a design optimization tool.
Intelligent Processing of Carbon-Black Loaded Plastics
Authors: Bouda V.
Published: March 2022

The electrical conductivity of alternating current (AC) and permittivity of carbon-black (CB)-filled low density polyethylene (LDPE) has been measured as function of time at a temperature higher than the melting temperature of matrix polymer. The conductivities measured at lower frequencies (If) can be used for the characterization of the properties of the interlayer between the CB-particles. The conductivities measured at higher frequencies (hf) reflects the properties of the internal structure of the individual CB-aggregate. At a characteristic time t°, the lf AC conductivity suddenly increased up to the hf conductivity and the permittivity suddenly decreased. The CB aggregates are probably linked together by paracrystalline layers after a certain time of annealing. The time t° increases with the weight percent of CB. It was also found that t° increases as the temperature of annealing decreases. The time t° is interpreted as a relaxation of potential energy of electrostatic repulsion forces between the reversible disintegrated CB particles. The poor reproducibility and stability of CB-filled plastics can be explained by the observed changes of conductivity.
Microstructural Optimization of a Functionally Gradient Layer
Authors: Nadeau Joseph C. , Ferrari Mauro
Published: March 2022

This paper addresses the microstructural optimization of an infinite, transversely isotropic layer which is free of tractions and subjected to a prescribed thermal gradient. The layer’s microstructure is characterized as a bi-phase composite in the form of a continuous matrix perfectly bonded to embedded spheroidal reinforcements. The microstructural characterization of the FGM is taken to be the volume fraction, aspect ratio and orientation distribution function of the second phase. The composite layer is made functionally gradient by taking the aforementioned parameters to vary through the thickness of the layer. The effective properties of the bi-phase composite are obtained by appropriate homogenization theories. The microstructural parameters are determined such that an objective function, defined in terms of strain energy and curvature, is minimized. Specific results are presented for an aluminum (Al) layer reinforced with silicon carbide (SiC). Comparisons are made to conventional coating technology.
Microstructure and Residual Stresses in FGMs
Authors: Zavaliangos Antonios
Published: March 2022

In this work we present preliminary results on the development of residual stresses due to differential thermal expansion and unloading from hydrostatic pressure that typically occur during the powder metallurgical processing of FGMs. Attention is focused in microstructures where the fractions of the two phases are equal.
A Unified Micromodel for Constitutive Behavior of Metal Matrix Composites Undergoing Plastic Deformation
Authors: Kwon Y. W. , Kim C. , Yang G. Y.
Published: March 2022

The objective of this study is to develop a unified, three-dimensional micromodel which can describe the nonlinear elastoplastic constitutive behavior of MMC’s with continuous fibers, particles, or aligned short fibers as the reinforcement. In the micromodel, both the reinforcement and the matrix may have elastic and/or elastoplastic deformation(s), respectively. However, as in most cases, the development is shown for elastic reinforcement in an elastoplastic matrix. The micromodel uses a repeating unit-cell model with eight subcells. For a particulate or an aligned short fiber composite, one center subcell represents the particle or the short fiber while the rest of the subcells represent the matrix. On the other hand, two aligned subcells indicate the fiber for a fibrous composite. The micromodel yields the overall effective constitutive equation for an MMC with elastoplastic deformation in the matrix material. The effective stress-strain plots of various MMC’s are predicted using the micromodel for a wide variation of the reinforcement volume fraction. These results are compared to those obtained from the finite element analysis, and the two results agree very well.
Effect of Fiber Volume Fraction on Fully-Reversed Isothermal Fatigue Behavior of Unidirectional SCS6/Ti-15-3 Composites
Authors: Subramanian Suresh , Castelli Michael G. , Lerch Bradley A. , Allen Dana
Published: March 2022

The present study focuses on characterizing the fully-reversed fatigue behavior of unidirectional SCS6/Ti-15-3 composites. Fatigue tests were conducted at 800 ° F on 8 ply 0 ° laminates with fiber volume fractions ranging between 15% and 42%. Anti-buckling guides were designed to prevent sample buckling under compressive loading. Axial and transverse strain was monitored during static and fatigue loading to obtain a quantitative estimate of damage and plasticity in the material. The static tensile strength of this material (at 800 °F) with fiber volume fraction between 15% and 42% ranged between 136 ksi (937 MPa) and 252 ksi (1736 MPa) and the Poisson’s ratio between 0.29 and 0.38. Fatigue test results indicated that the life of unidirectional MMC was independent of fiber volume fraction when compared on a strain range basis. Results also indicated that there was very little change in axial stiffness and Poisson’s ratio in laminates with 35% and 42% fiber volume fraction. Lower volume fraction samples showed larger changes in properties under fatigue loading.
Interphase Strength of Ti-MMC Using a Localized Stress Approach
Authors: Tamin M. , Ghonem H.
Published: March 2022

This paper determines the fiber/matrix interphase shear strength in a titanium matrix composite using the knowledge of the load corresponding to onset of interface debonding in fiber push-out experiments. Finite element calculations employing an axisymmetric cylinder model of a fiber embedded in the matrix phase are utilized to calculate the interphase stress distribution along the fiber. A region of stress localization along the interface due to geometrical constraints of the fiber push-out test configuration is simulated. The interphase shear strength is defined as the peak of the shear stress localization along the fiber where initial debonding would occur. The calculated strength considers the contribution of the process-induced residual stress field as modified by geometrical constraints of fiber push-out test configuration. Results of the interphase strength obtained using the proposed localized approach are compared with those calculated assuming a uniform distributed shear stress along push-out fibers.
Mechanics of Polymeric Composites Exposed to a Constant Heat Flux
Authors: Tuttle Mark E. , Mescher Ann M. , Potocki Mark L.
Published: March 2022

An analysis 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 levels 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 stress of 240 MPa and a 1-D heat flux level of 10 kW/m2 are presented. The predicted response is considered to be a reasonable representation of the expected behavior.
Stiffness Changes in Laminates Caused by Intralaminar Cracks and Shear Deformation
Authors: Varna Janis , Akshantala Nagendra V. , Talreja Ramesh
Published: March 2022

An experimental study has been conducted to study stiffness changes in laminates containing inclined (off-axis) plies. The class of laminates studied is glass-epoxy (0, ±θ4, 01/2)s with θ = 25, 40, 55 and 70. It is found that for θ > 40 multiple cracks occur in the θ-plies while for θ < 40 no cracks are found. However, for all θ angles the laminate moduli change. A continuum damage mechanics approach is used to calculate stiffness changes due to cracks. In the absence of cracks the shear modulus reduction in the θ-plies, determined from independent tests on a (±45)s laminate, is found to provide good prediction of the observed stiffness changes.
Soft Body Impact Damage Tolerance of Laminated and 3D Woven Composites
Authors: Weeks Craig A. , Bertke Robert S. , Laber Mark W.
Published: March 2022

The Affordable Composite for Propulsion (ACP) program is investigating material designs and manufacturing processes which produce affordable and structurally acceptable parts for turbofan engine applications. In order to evaluate material architectures for engine structures susceptible to bird impact events, soft body impact tests were performed on laminated and 3D woven composite flat panels. Material architecture variables such as graphite/glass hybridization, stitching and type of stitch fiber for laminated composites, and ply-to-ply and through thickness interlock weaves for 3D materials were investigated. The primary test results of interest were damage resistance (velocity or energy to initiate measurable damage) and damage tolerance (resistance of the panel to propagation of existing damage). The results of these experiments are presented, and the behavior of the various material architectures are compared and contrasted. Material architecture variables which increase the soft body impact damage resistance and tolerance will be noted.
Modifications to Classical Shear-Lag Models Required for Prediction of Laminate Degradation due to Fiber Failure and Associated Mechanisms
Authors: Solti James P. , Mall Shankar
Published: March 2022

Modeling advanced composite materials can quickly become overwhelming when one starts to consider detailed phenomenological behavior of multilayered off-axis laminates with microstructural damage development resulting from aggressive thermal and mechanical cyclic loading. As such, an attempt is underway to develop a comprehensive solution algorithm, formulated from first-principle (simplified) criteria, which provides reasonable estimates of laminate behavior. The objective is to develop a detailed model based upon a series of modules each of which is derived from simplified theories. The formulation of the model in this manner is intended to reduce the complexities associated with modifying detailed micromechanical (or other) models to account for a myriad of laminate geometries, damage mechanisms and loading conditions.

This paper is an extension of previous works presented by the authors which outline the development of a simplified micromechanics model as described above. In particular, this paper examines required modifications to classical shear-lag models for considering fiber failure and other associated mechanisms such as fiber pull-out and laminate failure. The approach adopted herein assumes the development of an “effective applied stress” to undamaged fibers neighboring fibers which have fractured and/or have slipped (pull-out). Both modifications to the equilibrium relationship, as well as the net effect on the laminate strain due to these damage mechanisms are explored under specific laminate and loading conditions.
Direct Observation of Contact Damage Produced by Vickers Indentation in Diamond-Like Films
Authors: Bulsara Vispi Homi , Chandrasekar Srinivasan , Farris Thomas N.
Published: March 2022

An experimental study has been made of film delamination and cracking produced by indentation of diamond-like films deposited on glass substrates. In the indentation experiments, a Vickers indenter was loaded normally against a film surface with the load being kept in the range of 2g to 300g. The contact region was observed and photographed in-situ using a high resolution, optical microscope and video imaging system, while the indentation load-history was measured with a piezo-electric force sensor attached to the indenter. The experiments have enabled detailed observations to be made of the contact damage such as the initiation of film delamination and cracks in the film; the loads at which these events occur and their evolution during loading and unloading; and the ejection of fractured film fragments from the substrate. The implications of these results to characterizing the relative failure resistance of various films and for estimating their cohesive and adhesive strengths are discussed.
Effects of PVD Coatings on Thermal Fatigue Resistance of Hot-Work Tool Steels
Authors: Wang Yucong
Published: March 2022

Physical vapor deposit (PVD) coatings have been used to extend die-casting die life, mainly by reducing molten metal’s corrosion and erosion to the dies. The dies are made of hot-work tool steels. Among the tested PVD coatings, CrN and TiAlN coatings provided the longest die life because of their higher oxidation resistance temperatures. Die insert life can be extended three to eight times based on the in-plant tests. However, the thermal fatigue resistance of hot-work tool steels was affected differently by the PVD coatings. The research work in this area is very limited.

This paper discusses the results from a systematic study involving three H series and two maraging hot-work tool steels with and without TiN, TiAlN or CrN PVD coating, in terms of thermal cycling induced fatigue (heat checking) resistance, hardness and fracture toughness changes, as well as molten aluminum corrosion resistance. Based on the results, a die life extension approach is proposed to reduce die-casting operation cost and improve casting quality.
The Fiber/Matrix Interface in Ceramic-Matrix Composites
Authors: Zhang Y. , Yu N.
Published: March 2022

The fiber/matrix interface plays a key role in the toughening mechanisms and overall thermo-mechanical behavior of fiber-reinforced ceramic-matrix composites (CMCs). A debonded fiber/matrix interface induces energy-absorption (i.e., toughening) mechanisms, such as interfacial sliding and fiber pull-out, and consequently results in the graceful, rather than catastrophic, failure of fiber-reinforced CMCs; see, for example, Evans and McMeeking (1986).
Thermal Expansion Behavior of Ceramic Composites for Thermal Management Applications
Authors: Shen Yu-Lin
Published: March 2022

The thermal expansion response of ceramic composites containing a metallic phase for thermal management applications is studied. The two types of composites considered include a SiC particulate/Al composite (with a large extent of particle contact due to high SiC content) and a SiC/Al interpenetrating composite. Numerical modeling using the finite element method is carried out to provide insights into the experimentally measured deformation behavior. It is found that processing induced residual porosity at the particle contact areas and the sharp concave comers of SiC can govern to a significant degree the thermal expansion response of the composites. The micromechanisms responsible for such effects are identified.
Cyclic Fatigue and Resistance-Curve Toughening in In Situ Toughened Silicon Carbide at Ambient to Elevated Temperatures
Authors: Gilbert C. J. , Ritchie R. O.
Published: March 2022

It is now well known that the principal source of toughening during resistance-curve (R-curve) behavior in non-transforming monolithic ceramics derives from crack-wake phenomena, in particular from a zone of bridging grains behind the crack tip which screen it from the applied loads (crack-tip shielding) (Evans, 1990). Specifically, where fracture is intergranular, the elastic and frictional tractions generated via the contact of opposing crack faces act to reduce the local driving force in the immediate vicinity of the crack tip. Indeed, various attempts have been made to quantify the magnitude and distribution of bridging tractions acting across the faces of cracks growing under monotonic loads in order to understand the mechanics of R-curve toughening and how it relates to local microstructure.
Characterizing Adhesion of Thermal Barrier Coatings
Authors: Gupta Vijay , Yu Allen
Published: March 2022

A previously developed technology of laser-generated stress pulses has been adapted to measure the tensile strengths of interfaces between composite thermal barrier coatings of alumina and zirconia, and steel substrates. In the basic technique developed previously (Gupta et al., 1994), a compressive stress pulse is generated on the back side of the substrate disc by exfoliating a constrained metallic film via the impingement of a Nd:YAG laser pulse. This compressive stress pulse propagates through the substrate and reflects into a tensile wave from the free surface of the coating that is deposited on its front surface. The returning tensile pulse pries off the interface if its amplitude is sufficiently high. The interface stress is determined by recording the coating’s free-surface velocity by using a laser displacement interferometer. Because of the short rise time of the stress pulse, an interfacial region of approximately 70 to 150 micrometers is uniformly stressed. This results in the failure of the weakest link in the region which is spanned by the coating, interface and the substrate material. In addition, such a short pulse is able to invoke a rather local response from the interface such that minute structural and chemical changes are directly reflected in the measured strengths.
Well-Dispersed Suspension Formation for Infiltration of Ceramic Fiber Preforms With SiC-Filled Polysiloxane Resins
Authors: Erdal Merve , Boschelli Marianne , Güçeri Selçuk
Published: March 2022

The development of low-viscosity preceramic polymers such as Blackglas™1, introduced new opportunities to the processing of ceramic-ceramic composites. Many polymer based liquid processing technologies that have been vastly investigated and established, can now be applied to ceramic composite processing with preceramic polymers. Resin transfer molding (RTM) is one of the most promising techniques adaptable to manufacturing of continuous fiber reinforced, ceramic composite structures with reliable, cost-effective properties. A major drawback of the process is the material loss in the preceramic polymer during processing, resulting in a porous structure that needs to be densified for satisfactory structural performance. This can be accomplished through several process cycles at the expense of cost-effectiveness. One way of reducing the number of cycles and obtaining near-net shapes during the process is the inclusion of inert and/or active filler particles in the polymer during injection.
A New Multiparameter Approach to the Characterization of Mechanical Properties of Ceramics
Authors: Soboyejo Alfred B. O. , Soboyejo Winston O.
Published: March 2022

This technical paper describes a new multiparameter approach, consisting of deterministic and mechanistically based characterization of the mechanical properties of structural ceramics; and the appropriate probabilistic models, from which the failure probabilities and the reliabilities of engineering components made with such structural materials can be evaluated, for structural, mechanical and aerospace engineering design applications. For example, the practical application of the methodology developed can be demonstrated by the actual characterization of the mechanical properties of some new structural ceramics which are being developed for high-temperature engineering design applications.
In Situ Observation and Modeling of Damage Modes in Cross-Ply Ceramic Matrix Composites
Authors: Kim Ran Y. , Tandon G. P.
Published: March 2022

Ceramic-matrix composites generally exhibit matrix and/or interface damage well before final failure because of the low strain capability of the brittle matrix and weak interfacial bonding. These damages have a significant influence on the stress-strain behavior as well as on the ultimate strength of the composite. The failure process in a multidirectional laminate is further complicated by its dependence on ply orientations and stacking sequence Reported in this paper are the results of both analytical and experimental investigations carried out in an attempt to understand the initiation and propagation of damage in a [0/90]3S cross-ply laminate. A glass-ceramic matrix composite reinforced with silicon carbide (Nicalon) fibers is investigated at room temperature under uniaxial tensile loading. The initiation and propagation of interfacial debonding, microcracking, and fiber breaks were observed in situ, under applied load using a specially built loading device. The observed damage modes were then incorporated into existing micromechanical models to predict the laminate stress-strain behavior and compared with the experimental measurements.
Axisymmetric Microfracture Analysis of Fiber-Reinforced Brittle Composites
Authors: Zhang Hanqing , Liaw Benjamin , Delale Feridun
Published: March 2022

In many ceramic matrix composites subjected to tensile loading the damage usually starts with matrix cracking followed by multiple matrix cracking, interfacial debonding, fiber breaking and fiber pull-out. Some of these events may occur simultaneously and the specimen may separate into two or more pieces. Indeed our tensile testing of Nicalon/CAS II composites in SEM confirms this general damage pattern, which resulted in a nonlinear stress-strain curve. The analytical challenge is to construct a damage model which can predict or at least simulate the observed behavior. The linear part of the stress-strain curve corresponds to the undamaged stage of the specimen and the slope can easily be matched using the “rule of mixtures”. The non-linear portion will depend on the assumed damage model.
Mechanisms for Size Effects in Bending of Fiber Composites
Authors: Swanson Stephen R.
Published: March 2022

The size of the specimen or structure has often been cited as having an effect on the apparent strength of fiber composites. Bend tests are often used to infer size effects, as the stressed volume is typically smaller than in uniform tension or compression test specimens. However bend tests also have a stress gradient through the thickness. In the present work a model is developed for compression failure of fiber composites that includes through-the-thickness effects. A primary feature of the model is that through-the-thickness shear stresses are predicted to occur because of the varying bending displacement of the wavy fibers. These shear stresses have a stabilizing effect on the fibers, and thus raise the apparent compressive strength. When applied to bend tests, the model predicts that the apparent compressive strength of fiber composites will depend on the specimen thickness, in accord with experimental evidence in the literature. The result is that through-the-thickness effects are predicted to affect the compressive strength of fiber composites, and this effect is distinct from a true size effect.
Scaling Effects in Composite Laminates Under Tensile, Flexural, and Compressive Loading
Authors: Johnson David P. , Felts Joseph H. , Ho Michael T.
Published: March 2022

It has been demonstrated by several researchers that composite materials exhibit scaling effects both in unidirectional and multidirectional specimens. This has an important impact on the design and manufacture of full scale structures. In the current work, the authors present a wide range of experimental data for scaled composite laminates under tensile, flexural and compressive loading. Data for both blocked ply (so-called ply-level) and distributed ply (so-called sublaminate-level) thickness scaling are presented. Laminates studied include the following stacking sequences: [45/-45/45/-45]s, [45/-45/0/90]s, [45/-45/90/0]s, [45/90/-45/0]s, [45/-45/45/-45/0]s, [45/-45/0/0]s, [90/0/90/0]s. In general, ply-level scaling leads to degraded performance with increased specimen size in all stacking sequences, under all loading conditions. Sublaminate-level scaling also leads to a lowering of strength and strain to failure, although the effect is much less pronounced than in ply-level scaling. Typically, the strength of these specimens decreases by about 5% as the size of the specimens is quadrupled.
Size Effects in Tensile, Compressive and Interlaminar Failure of Unidirectional Composites
Authors: Wisnom Michael R.
Published: March 2022

A summary is given of experimental results on size effects for different failure mechanisms from geometrically scaled tests on unidirectional composites. Size effects for tensile failure were observed from three sets of scaled flexural tests in a four point bending rig for both glass and high strength carbon fibre/epoxy. Tests on intermediate modulus carbon fibre/epoxy in a pin-ended buckling rig produced compressive failures, and showed a larger size effect than for tensile failure. Scaled curved beam bending tests were used to investigate size effects in interlaminar tensile strength, and short beam shear tests for interlaminar shear strength. Significant size effects on interlaminar strength were found for both glass and carbon fibre/epoxy.
Statical and Vibrational Behavior of Orthogonally Reinforced Flat Panels Exposed to Thermomechanical Loading
Authors: Souza M. A. , Librescu L.
Published: March 2022

A number of results related with the non-linear response of orthogonally stiffened flat panels exposed to thermomechanical loading are presented. The results concern both the statical and vibrational responses.

The effects played in this context by the various reinforcement schemes and the initial geometric imperfection are considered and pertinent conclusions are highlighted. The paper constitutes a completion of a number of results previously reported by the authors of this paper (see Librescu and Souza (1992, 1997) and Souza and Librescu (1995).
Vibration of a Flexible Solar Array Caused by the Change of Thermal Input in Orbit
Authors: Tabacchi Luca , Natori M. C. , Hirikado Hiroshi
Published: March 2022

Behaviour of large flexible space structures (antennas, solar arrays, frames of space stations, etc.) is strongly influenced by thermal loads in orbit. Thermally induced forces can affect flexible space structures in several ways: thermal buckling and thermally induced vibrations due to relatively rapid heating are two typical phenomena. In orbit attitude disturbances of an actual spacecraft are presented as a remarkable example of such phenomena. Analytical models are developed and numerical simulations performed in order to demonstrate that the vibration of the spacecraft flexible solar arrays is the most likely disturbance source. The results are shown to be in agreement with flight data and laboratory tests.
Thermomechanical Response of Laminated Flat Panels Featuring Interlaminar Bonding Imperfections
Authors: Icardi U. , Librescu L. , Sciuva M. Di
Published: March 2022

In this study the problem of the implications played by the sliding interlaminar imperfections on the static and dynamic non-linear behavior of laminated composite flat panels subjected to thermomechanical loadings is addressed. Towards the end of approaching this problem, a recently developed geometrically non-linear theory of anisotropic composite flat panels featuring interlaminar bonding imperfections is used. A number of results related with the influence of interfacial bonding imperfections on the thermomechanical postbuckling and frequency-load-temperature interaction are supplied and pertinent conclusions are outlined.
A Finite Element Modal-Coordinate Formulation for Thermal Postbuckling of Composite Plates
Authors: Shi Yucheng , Lee Raymond Y. Y. , Mei Chuh
Published: March 2022

A finite element formulation in modal coordinates is developed for nonlinear thermal postbuckling of thin composite plates. The linear buckling mode shapes used to model the postbuckling deflection are investigated. The participation from each mode to the postbuckling deflection is presented quantitatively. The minimum number of modes for convergent solution can be assured. Postbuckling of symmetrically laminated, antisymmetric angle-ply, and unsymmetrically laminated composite plates under mechanical and thermal loads are studied. Deflection shape changes are observed in long rectangular plate. Multiple postbuckling solutions or branches are obtained for plate under combined mechanical and thermal loadings.
Oscillation Control of Cantilevers via Smart Materials Technology and Optimal Feedback Control: Actuator Location and Power Consumption Issues
Authors: Na S. S. , Librescu L.
Published: March 2022

A study of the vibration control of cantilevers exposed to blast pressure signatures is presented. Whereas the structure used in this analysis is in the form of a thin-walled beam of closed cross-section contour, the control is based upon the simultaneous implementation of the adaptive materials technology and the optimal feedback control.

Issues related with the influence upon dynamic response of size and location along the beam span of piezoactuator patches are investigated and the efficiency of this combined control methodology is outlined. Other issues related with the minimization of the input power required in the control process, maximization of the sensing voltage output and implications of the limitation of control input voltage on dynamic response are also addressed and pertinent conclusions are outlined.
Design Criteria for Sandwich Panels for Building Construction
Authors: Davies J. Michael
Published: March 2022

Sandwich cladding panels comprising two metal skins and a lightweight insulating core are finding ever-increasing use as the wall and roof cladding for a wide range of building types. Their main attraction is their outstanding thermal performance but the designers and specifiers of such panels, and competing cladding systems, have to consider a wide range of other parameters in order to arrive at the best solution for their design requirements. This paper gives an overview the current scene, with particular reference to Europe, and makes specific comments on some of the current issues. Naturally, the structural design is discussed but particular attention is also paid to some of the other issues such as fire performance and durability which are less well documented.
Consideration on the Benefits of Intentional Blade Mistuning for the Forced Response of Turbomachinery Rotors
Authors: Castanier Matthew P. , Pierre Christophe
Published: March 2022

The intentional mistiming of blades in order to reduce the forced response amplitudes of turbomachinery rotors is considered. The statistics of the maximum blade response amplitudes for a simple model of a 12-bladed disk are investigated. It is shown that the maximum response amplitudes are appropriately modeled by a Type III Weibull distribution. Intentional mistuning is introduced into the model by varying the nominal blade stiffnesses in rotationally periodic patterns. Of the six non-zero harmonics, the first and second harmonics are shown to provide a significant decrease in the maximum amplitudes. A more practical, pseudo-harmonic-two configuration of mistuning is also considered. This pattern requires only two unique blade designs, and it results in an even larger decrease in the maximum response than that provided by the harmonic-two intentional mistuning.
Comparison of Fretting Fatigue Crack Nucleation Experiments to Multiaxial Fatigue Theory Life Predictions
Authors: Szolwinski Matthew P. , Harish G. , Farris Thomas N.
Published: March 2022

Fretting is associated with microslip at the interface of contacts experiencing oscillatory loads. One consequence of fretting is the formation and subsequent growth of cracks at the edge of contact, a phenomenon known as fretting fatigue. Fretting fatigue is an important high cycle fatigue failure mechanism in aircraft structural lap joints and turbine blade/disk contacts. A well-characterized, integrated fretting test system has been developed in which both normal and cyclic tangential fretting loads are applied and monitored in conjunction with a bulk load on the specimen. The experimental data includes histories of the three applied forces and a detailed record of the evolution of interfacial friction coefficient, as driven by the surface microslip. The experimental system has been exercised to observe fretting crack nucleation and growth under a wide range of loading conditions in the context of a statistically-designed test matrix. An extensive multiaxial fatigue analysis based on the stress-strain cycle experienced by each point of the bodies subjected to the fretting loads reveals that the critical location for crack formation is the trailing edge of contact, consistent with observations made in the laboratory. The resulting stress-strain cycles are coupled with strain-life theory and literature values of uniaxial fatigue constants to predict fretting fatigue crack nucleation. The data collected for 2024-T351 aluminum alloy correlates very well with this prediction.