Multiple Laminates Research Articles

New iteration fractal branch and bound method for stacking sequence optimizations of multiple laminates

For laminated composite materials, the stacking sequence design is indispensable to make efficient use of the material properties. Laminated composites are usually fabricated from unidirectional plies of given thickness with limited fiber orientations to a small set of angles (e.g. 0°, +45°, 45°, and 90°). An improved version of fractal branch and bound method has been proposed to optimize multiple stacking sequences. The improved method, however, cannot be applied to complicated structures, since it is difficult to determine which is the most effective surface for designing such structures. In the present study, therefore, a new iteration fractal branch and bound method is proposed, which does not require empirical knowledge of the target structure. Here, this method is applied to a hat-stiffened panel to enable the stacking sequences of the two panel laminates and hat-type stiffener to be optimized simultaneously.

Modeling of Diffusion with Partitioning in Stratum Corneum Using a Finite Element Model

Partitioning and diffusion of chemicals in skin is of interest to researchers in areas such as transdermal penetration and drug disposition, either for risk assessment or transdermal delivery. In this study a finite element method is used to model diffusion in the skin's outermost layer, the stratum corneum (SC). The SC is considered to be a finite two-dimensional composite having different diffusivity values in each medium as well as a partition coefficient at the interfaces between media. A commercial finite element package with thermal analysis capabilities is selected due to the flexibility of this software to handle irregular geometries. Partitioning is accommodated through a change of variables technique. This technique is validated by comparison of model results with analytical solutions of steady-state flux, transient concentration profiles, and time lag for diffusion in laminates. Two applications are presented. Diffusion is solved in a two-dimensional "brick and mortar" geometry that is a simplification of human stratum corneum, with a partition coefficient between corneocyte and lipid. Results are compared to the diffusion in multiple laminates to examine effects of the partition coefficient. The second application is the modeling of diffusion with partitioning through an irregular geometry which is obtained from a micrograph of hairless mouse stratum corneum.

Realizable (Average Stress, Average Strain) Pairs in a Plate with Holes

Here a complete characterization is given of the set of all possible (average stress, average strain) pairs that can exist in a plate containing a fixed volume fraction f of holes. Specifically, for a given average stress, the range of values the average strain takes as the microgeometry is varied (while keeping f fixed) is determined. It is shown that multiple rank laminate materials suffice to generate all possible values of the average strain. When the microgeometry is restricted to be a periodic array of holes, with only one hole per unit cell, the average strain takes a smaller range of values as the hole shape is varied. A certain necessary condition for optimality must be satisfied if the hole is such that the average strain is on the boundary of this range. Numerical results are obtained for the range in the limit where the holes are well separated and occupy a small volume fraction. Optimal hole shapes, associated with average strains on the boundary of the range of admissible values, are identif...

Parametric optimisation of composite shell structures for an aircraft Krueger flap

This paper details the conceptual design optimisation of the configuration and composite lay-ups used to replace the conventional honeycomb stiffened structure of a Krueger flap. The multiple composite laminates selected for redesigning the lay-ups within an initial symmetrical quasi-isotropic ply configuration of [0/45/−45/90] s, had to demonstrate full orthotropic characteristics. In order to construct a numerical process to optimise the required multi-layered composite shells, a commercial finite element code, Ansys, was used to develop a parametric analysis file. This analysis subroutine was then integrated into an Ansys Parametric Design Language code embedding the objective of the optimisation process––mass minimisation––as well as all the constraints and the allowable domains of the parameters. The paper, in its conclusion, presents a comparison between the original product and the optimal design, and reviews the advantages of the future implementation of this design.

Stacking sequence blending of multiple composite laminates using genetic algorithms

This paper presents a methodology for designing any two-dimensional array of laminated composite panels with varying loads such that continuity of some or all of the plies is maintained across adjacent panels. This design process is commonly referred to as blending and is beneficial in helping to minimize the manufacturing effort and cost of the panels while meeting structural requirements at minimum weight. The methodology discussed here involves an automated 2-step optimization process using a commercial genetic algorithm software code called DARWIN. The methodology is tested using a 3×3 array of sandwich panels, and an 18-panel group arranged in a horseshoe pattern. Results for each design problem are generated using ADOPTECH's Java-based composite laminate design software called OLGA, which utilizes the DARWIN optimization engine. A comparison between the individually optimized panels designs and the blended designs for each design problem is also presented.

Ultrastructural characterization of microvasculature in photoaging

The cutaneous microvasculature was examined by electron microscopy in order to compare its characteristics in photodamaged preauricular skin and in sun-protected postauricular sites of 15 Japanese women aged 58–81 years. The characteristic ultrastructural features of the microvasculature in photodamaged skin compared with those in sun-protected skin included dilated vessels embedded in elastin which depressed endothelial cells, vessels surrounded by a thick amorphous material composed of multiple laminations of a basement membrane-like material, and activated endothelial cells which had increased numbers of cytoplasmic organelles and pinocytotic vesicles. A novel finding of this study in photodamaged vessels was an increased formation of new vessels (angiogenesis) via two distinct pathways. In severe elastosis, activated endothelial cells with densely packed intracytoplasmic microfilaments extended large pseudopods into the elastotic material. In contrast, isolated mesenchymal cells, which possessed immature Weibel–Palade bodies, were scattered around pre-existing vessels within the Grenz zone. In some cases, many mesenchymal cells with electron-lucent cytoplasms aggregated and interconnected by cytoplasmic processes, which was followed by the formation of vascular structures. These results suggest that there are significant ultrastructural differences in vessels between photoaged and intrinsically aged facial skin and that the photodamaged microvascular system is characterized by the co-existence of regressive changes and angiogenesis.

Impact perforation resistance of laminated and assembled composite plates

A previous study on impact response of composite laminates concluded that impact perforation was the most important damage stage in composite laminates subjected to impact loading since impact characteristics and degradation of mechanical properties of composite laminates reached critical levels once perforation took place. It was also found that thickness had a greater influence on impact perforation resistance than in-plane dimensions. However, as the composite laminates became very thick, the manufacturing cost for obtaining high-quality composite laminates could become unaffordable. In an effort to meet design requirements and to reduce manufacturing costs, assembled composite plates, which were organized by assembling multiple thin composite laminates together, were considered as alternatives to thick laminated composite plates. Various joining techniques including mechanical riveting, adhesive bonding, stitching and their combinations were used in assembling two- and four-laminate plates. Experimental results revealed that epoxy bonding outperformed other joining techniques. Although good bonding resulted in a higher impact bending stiffness and subsequently a higher perforation threshold, increasing the laminate thickness, or the number of laminates, was found to be more efficient in raising perforation threshold than improving the joining stiffness. As a major finding of the study, the assembled composite plates were found to have perforation thresholds similar to the laminated counterpart. Hence, the former could be used to replace the latter, at least, as far as perforation threshold was concerned.

Effects of joining techniques on impact perforation resistance of assembled composite plates

A previous study on impact response of composite laminates concluded that impact perforation was the most important damage stage in composite laminates subjected to impact loading, since impact characteristics (peak force, contact duration and absorbed energy) and mechanical properties degradation of composite laminates reached critical points once perforation took place. It was also found that thickness had a greater influence on impact perforation resistance than did in-plane dimensions. However, as the composite laminates became very thick, the manufacturing cost for obtaining high-quality composite laminates increased. In an effort to meet design requirements and reduce manufacturing costs, assembled composite plates, which were organized by assembling multiple thin composite laminates, were considered as alternatives for thick single-laminate composite plates. Various joining techniques including mechanical riveting, adhesive bonding and stitch joining, and their combinations, were used in assembling two- and three-laminate plates. Experimental results revealed that adhesive bonding outperformed other joining techniques. Although good bonding resulted in higher joining (bending) stiffness and subsequently higher perforation thresholds, increasing the laminate thickness or the number of laminates was found to be more efficient in raising perforation threshold than in improving the joining stiffness. The assembled three-laminate plates were found to have higher perforation thresholds than their thick single-laminate counterpart.

Fracture of metal/ceramic laminates—I. Transition from single to multiple cracking

The transition from single crack extension to multiple laminate cracking near the crack tip has been studied over a range of metal/ceramic thickness ratios ( t m/ t c), in three metal/ceramic laminate systems: Al/alumina, Cu/alumina and Ni/alumina. Multiple cracking occurs above a critical value of t m/ t c, with the critical value increasing with decreasing ratio of equivalent constrained metal yield stress to mean ceramic fracture stress, σ e/ σ c. These results are shown to be inconsistent with the predictions of a linear elastic fracture mechanics (LEFM) model, which considers a cracked laminate as a bridged monolithic crack, for the lower metal yield strength Cu/alumina and Al/alumina laminates. A modified model considers a limiting case where the stress distribution in the ceramic layers in the crack wake is determined by shear-lag below a critical value of the ratio σ e/ σ c. This combined model is shown to predict more accurately the transition from single to multiple cracking in the three laminate types and also to predict the ceramic layer crack spacing in the multiple cracked specimens.

The large, low mass Al–CFC–Aramid compound vacuum chamber for the Sindrum II μ–e-experiment at PSI: (design, testing and operation)

This work presents the production method of a vacuum vessel of large diameter and volume with small density and low Z materials by the use of multiple lamination techniques.

Electromagnetic flat-faced robot gripper for handling multiple industrial transformer core lamination plates

In the industrial transformer core assembly process, significant productivity gains can be achieved by utilizing a robotic gripper that is able to handle, and accurately position, multiple transformer laminations during each pick-and-place cycle. This paper reports on the development of a novel electromagnetic lifter for such applications. The lifter has the unique capability to selectively pick a given number of laminations at a time (the usual requirement is three) from a stack. By considering an analytical model of the magnetic circuit of the electromagnet-lamination stack combination, closed form solutions are obtained for the flux flow pattern and the lifting force on each lamination in the stack which closely agrees with the numerical results obtained using two-dimensional finite element analysis software. Results of experiments conducted on a prototype electromagnet are also presented that validate the analytical model findings.

Effects of general laminations and boundary constraints on vibration of composite shallow shells

This paper presents a comprehensive parametric study on the essential effects of symmetric and unsymmetric fibre orientations on vibration of thin, composite double curved (cylindrical, spherical and hyperbolic paraboloidal) shallow shells with arbitrary and complex boundary constraints. The precise strain and kinetic energy integral expressions for the laminates are formulated by using the extremum energy principle with no restrictions on the number of laminations and fibre orientations. A versatile and flexible general method of solution for vibration of composite laminates is developed. Convergence and comparison studies are reported to verify the consistency and accuracy of this analysis method. New results are presented for simply supported and fully clamped laminated shells with multiple laminations, symmetric and unsymmetric stacking sequences for two types of composite materials. The influence of fibre angles and stacking sequences on vibration mode shapes is also illustrated.

The effect of multiple damage in composite structures: a theoretical investigation

This paper focuses on the problem of damage in composite structures and discusses the theoretical analysis of the effect of multiple damaged composite laminates subject to uniaxial and bi-axial loading. The interaction effect between two 27.5 mm diameter delaminations, with 9.5 mm diameter holes, was studied using a 3-D finite element analysis as a function of damage spacing. The compressive loads required for delamination growth were predicted using a Strain Energy Release Rate approach, viz. T ∗ -integral. The results indicated that, for the particular layup analysed, the damage interaction can be considerable as the distance between the damage is reduced. The interaction effect appears to substantially increase T ∗ i.e. reduce the compressive load required for delamination growth, if the row of multiple damage is perpendicular to the applied load. T ∗ also appears to increase, for all the cases considered, when bi-axial loading is applied.

Directional symmetry of the time lag for downstream absorptive permeation studied by the matrix method

The directional symmetry of the downstream time lag for absorptive permeation, accompanying a first-order reaction, across a heterogeneous membrane has been proven by the matrix method based on the theory of Siegel. Owing to the heterogeneity the partition coefficient (K), diffusivity (D) and rate constant (k) are all dependent on position. The directional symmetry was first shown for multiple laminates with each laminate having a distinct K, D and k. The transmission matrix of the system is then a sequential product of those of the individual laminates. The proof is for the unit value of the determinant of the transmission matrix for each laminate and, hence, for the whole system. Directional symmetry is thus proven for the heterogeneous membrane, since it can be visualized to be an assembly of an infinite number of infinitely thin, homogeneous laminates.

Velocity measurements in polyetheretherketone-carbon fiber composite using excimer laser generated ultrasound

It is demonstrated that KrF laser ablation provides a suitable source for short pulse ultrasound generation in polyetheretherketone (PEEK)-carbon fiber composite. Measurements of plane wave velocities have been made on thin single laminae (∼130 μm thick) and multiple ply laminates of this anisotropic composite. Velocities for propagation at various angles with respect to the fiber axis have been measured and are shown to be in good agreement with theoretical calculations based on mechanical modulii.

DIFFUSION LAG TIME FOR MULTIPLE AND PERIODIC LAMINATES

The permeability and lag time for a heterogeneous diffusion system, in which the diffusivity and partition coefficient for the diffusant are dependent on position, are formulated in terms of a linear asymptotic analysis. A repeated integration of the diffusion equation is used to obtain the time dependence of the total solute release into the receiver, Q(t). The asymptotic form of Q(t) is linear in time. The slope, and intercept of this linear asymptote with the time axis, respectively, give formulas for the steady-state permeability and lag time. These formulas are then applied to diffusion systems of multiple laminates, consisting of a series of different homogeneous slabs. Thus, for the first time, a concise treatment of diffusion in multiple laminates is obtained. The formulas are also applied to periodic laminates, consisting of a series of identical slabs, but with position-dependent diffusivity and partition coefficient. We found that the lag time can be well approximated by (nh))2/(6D eff), where ...

Molluscum contagiosum associated with AIDS: a case report with ultrastructural study

The clinical features of perioral molluscum contagiosum in a patient with the acquired immunodeficiency syndrome are described. Light microscopy and thin section electron microscopy revealed epidermal cells in different stages of degeneration showing two types of cytoplasmic inclusions. The basement membrane exhibited discontinuities and multiple laminations which may be a response to viral-induced cytotoxic effects.

Micromechanisms of crack extension in composites

Abstract Typical engineering composites consist of brittle fibres, such as glass or carbon, in a weak, brittle, plastic matrix such as epoxy or polyester resin. An important characteristic of these composites, however, is that they are surprisingly tough, largely as a result of their heterogeneous nature and the manner of their construction. During deformation, microstructural damage is widespread throughout the composite, but much damage can be sustained before load-bearing ability is impaired. Beyond some critical level of damage, failure may occur by the propagation of a crack which usually has a much more complex character than cracks in homogeneous materials. Crack growth is inhibited by the presence of interfaces both at the microstructural level between fibres and matrix and at the macroscopic level as planes of weakness between separate laminations in a multiple laminate. The fracturing of a composite therefore involves not only the breaking of the load-bearing fibres and the weak matrix, but a co...

Scanning electron microscopy of some recent and fossil nodosariid f oraminifera

23 recent and fossil species representing 15 genera within the Nodosariacea have been studied with respect to lamellarity. All forms were found to be monolamellar. However, four different categories of the monolamellar construction pattern were found. Of these the ortho-monolamellar type has a one-layered chamber with an enveloping secondary lamella covering the earlier exposed shell. If the secondary lamella covers only part of the earlier exposed shell it is termed plesio-monolamellar while a lack of secondary lami­nation is called atelo-monolamellar. Multiple lamination in the septa covering also the eaiilier exposed shell parts is called poly-monolamellar. The microgranular layer in Jurassic forms is of diagenetic origin.

Influence of intermediate layers on coercive force of laminated Co-P films

This paper investigated the coercive force (H c ) of laminated Co-P films. The films were laminated by introducing intermediate layers of Pd ( T \sim 25 A) or nonmagnetic Ni-P (T = 250 A) between the Co-P films. The thickness of the Co-P films was varied from 650 A to 2600 A but was maintained constant within any series of laminations. The H c was evaluated as a function of total thickness for multiple Co-P laminate thicknesses up to 10,000 A. The H c of laminated Co-P films with intermediate Pd layers increased with total lamination thickness regardless of the thickness of the individual Co-P film. However, Co-P laminates deposited from a dilute solution with intermediate layers of Ni-P exhibited H c values independent of the total lamination thickness. The H c was independent of the total lamination thickness regardless of the base material provided Ni-P was deposited as the substrate. The magnitude of the H c was dependent on the Co-P film thickness. The H c of such Co-P laminates can be adjusted from 340 Oe to 700 Oe by selection of the appropriate thickness of the Co-P film. Co-P laminates deposited from a concentrated solution with intermediate layers of Ni-P exhibit H c values which decrease with total lamination thickness. These films exhibited lower H c values than nonlaminated Co-P films.