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The purpose of this paper is to investigate the buckling strength of simply supported plates with mechanical extension-twisting coupling. Bounds of the compression buckling strength are presented for a special sub-class of extension-twisting coupled laminate that is free from the thermal distortions that generally arise in this class of coupled laminate as a result of the high temperature curing process. These special laminates are generally referred to as hygro-thermally curvature-stable (HTCS).

This paper gives an overview of the methodology for developing laminates with extension-twisting coupling properties, which are derived from a parent laminate with HTCS properties. A closed form buckling solution is applicable for this special class of coupled laminate, which facilitates an assessment of compression buckling strength performance for the entire laminate design space.

Extension-twisting coupled laminates have potential applications in the design of aero-elastic compliant rotor blades, where the speed of the rotating blade, and the resulting centrifugal force, can be used to control blade twist. Extension-twisting coupling reduces the compression buckling performance of the blade, which represents an important static design constraint. However, the performance has been shown to be higher than competing designs with extension-shearing coupling in many cases.

Bounds of the buckling curves have been presented for the entire HTCS laminate design space, possessing extension-twisting and shearing-bending coupling, in which the laminates contain standard ply angle orientations and up to 21 plies. These laminates can be manufactured without the undesirable thermal warping distortions that generally affect this class of coupled laminate, and in particular, those containing angle plies only; previously thought to be the only form of laminate design from which this particular type of mechanical coupling can be derived.

With the ever increasing demands for high performance electronic devices there is a need for circuit board laminates that have enhanced properties when compared to conventional materials such as the widely used epoxide‐based FR4 laminates. Equipment manufacturers require boards with better mechanical stability and improved electrical characteristics. At the same time, new environmental legislation is set to drive electronics assembly temperatures much higher as manufacturers start to use lead‐free soldering processes. The legislation is also raising questions about the long‐term viability of brominated resins as the basis for imparting flame retardancy to laminates. Fortunately, laminate manufacturers have responded to these challenges by developing and introducing a wide range of new laminates that address these issues. This paper describes some of these challenges and gives an introduction to the new high performance laminates that are finding increasing use. It also highlights the need for chemical processes used in the manufacture of interconnects with laminates to be specifically optimised for the chosen substrate material.

The purpose of this paper is to report the preparation, characterisation and machinability of resin hybrid GFRP composites, which are made of glass fibre and the mixture of epoxy & polyester resin.

Resin hybrid GFRP laminates containing 0, 20 and 40wt% of polyester resin with the epoxy resin are prepared by conventional hand layup technique using glass fibre as the reinforcement. The variation of break load and shear strength for three different combinations of epoxy and polyester resin are studied by ASTM. A plan of experiment based on Taguchi was established with prefixed cutting parameters and the machining was performed. A stylus type profilometer to examine the surface roughness and shop microscope to examine the delamination of resin hybrid GFRP laminates were used. An analysis of variance (ANOVA) was performed to investigate the cutting characteristics of resin hybrid GFRP composite materials using solid carbide end mill. The correlation was obtained by multiple‐variable linear regression using Minitab 14 software.

Taguchi analysis reveals that the resin hybrid GFRP laminate provides better machinability in terms of surface roughness and delamination when compared to homogenous GFRP laminates (pure epoxy resin). Polyester resin enhances the machinability of the GFRP laminates.

The machinability of the resin hybrid GFRP laminates can be improved further by modifying the polyester resin percentage.

The resin hybrid GFRP laminates so developed can be used in aircraft and aerospace applications to increase the shear and work of fracture properties.

For TAB tapes and flex circuitry, laminates with adhesives (3‐layer laminates) are commonly used. The drawbacks of adhesives are well known. Adhesiveless flexible copper‐polyimide laminates (2‐layer laminates) could avoid such disadvantages. Two‐layer thin film laminates may be produced using sputtering technology. Good adhesion strength between the copper and the polyimide film may be achieved by means of special plasma treatment. The advantages and disadvantages of 2‐layer flexible thin film laminates are discussed in this paper, along with their different production methods. The adhesion strength of 2‐layer laminates in comparison with 3‐layer laminates will be pointed out. Future uses of 2‐layer flexible thin film laminates will be considered, along with their benefits.

Engineering composite laminates/structures are usually subjected to complex and variable loads, which result in interlayer delamination damage. However, damaged laminate may cause the whole structure to fail before reaching the design level. Therefore, the purpose of this paper is to develop an equivalent model to effectively evaluate compressive residual strength.

In this paper, taking carbon fiber reinforced composite T300/69 specimens as the study object, first, the compressive residual strength under different impact energy is obtained. Then, zero-thickness cohesive elements, Hashin failure criteria and Camanho nonlinear degradation scheme are used to simulate the full-process simulation for compression after edge impact (CAEI). Lastly, based on an improved Whitney–Nuismer criterion, the equation of edge hole stress distribution, characteristic length and compressive residual strength is used to verify the correctness of the equivalent model.

An equivalent relationship between the compressive residual strength of damaged laminates and laminates with edge hole is established. For T300/69 laminates with a thickness of 2.4 mm, the compressive residual strength after damage under an impact energy of 3 J is equivalent to that when the hole aperture R = 2.25 mm and the hole aperture R = 9.18 mm when impact energy is 6 J. Besides, the relationship under the same size and different thickness is obtained.

The value of this study is to provide a reference for the equivalent behavior of damaged laminates. An equivalent model proposed in this paper will contribute to the research of compressive residual strength and provide a theoretical basis for practical engineering application.

The tensile behavior of additively manufactured nylon-based carbon fiber-reinforced composites (CFRP) is an important criterion in aerospace and automobile structural design. So, this study aims to evaluate and validate the tensile stiffness of printed CFRP composites (low- and high-volume fraction fiber) using the volume average stiffness (VAS) model in consonance with experimental results. In specific, the tensile characterization of printed laminate composites is studied under the influence of raster orientations and process-induced defects.

CFRP composite laminates of low- and high-volume fraction carbon fiber of different raster orientations (0°, ± 45° and 0/90°) were fabricated using the continuous fiber 3D printing technique, and tensile characteristics of laminates were done on a universal testing machine with the crosshead speed of 2 mm/min. The induced fracture surface of laminates due to tensile load was examined using the scanning electron microscopy technique.

The VAS model can predict the tensile stiffness of printed CFRP composites with different raster orientations at an average prediction error of 5.94% and 10.58% for low- and high-volume fiber fractions, respectively. The unidirectional CFRP laminate composite with a high-volume fraction (50%) of carbon fiber showed 50.79% more tensile stiffness and 63.12% more tensile strength than the low-volume fraction (26%) unidirectional composite. Fiber pullout, fiber fracture and ply delamination are the major failure appearances observed in fracture surfaces of laminates under tensile load using scanning electron microscopy.

This investigation demonstrates the novel methodology to study specific tensile characteristics of low- and high-volume fraction 3D printed CFRP composite.

The influence of the number and arrangement of bolts on the tensile properties of bolted composite laminates was studied in the present study.

Based on the finite element model, the stiffness degradation method is used to simulate the damage evolution process for the failure of bolted composite laminates. Using ABAQUS finite element software combined with material failure criteria, the numerical calculation of the connection strength and failure mode of bolted composite laminates was carried out.

The results of the study show that the tensile strength of the composite laminates connected by three bolts is higher than that of the laminates connected by two bolts. And the arrangement of different bolts has a great influence on the failure strength of bolted laminates.

Bolted connection of composite laminates is a common problem in engineering practice. The effect of bolt arrangement and number on the strength of composite laminates is studied in this manuscript.

The purpose of this paper is to help high frequency circuit designers understand how to choose the best permittivity value for a laminate material for accurate modeling.

In this paper, experimental measurements of the performance of simple circuits are compared to various mathematical and software models.

Higher permittivity values were obtained using samples with bonded copper foil compared to samples etched free of foil. These higher values yielded better agreement between measured and modelled performance using current automated design software. High profile foil on thin laminates was found to increase the surface impedance of the conductor and change the propagation constant and apparent permittivity of the laminate by 15 percent or more. It was also demonstrated that, under some circumstances, the anisotropy of the substrate could result in differences in measured and modelled performance.

Only a limited number of circuit laminate materials were closely examined. Future work should include a wider variety of laminates.

The paper details the magnitude of the effects of test method, conductor profile and substrate anisotropy on the values of a material's permittivity best suited for circuit design purposes.

The purpose of the study was to develop the forming methodology for FML laminates with complex shapes, based on aluminium and epoxy-glass composite.

The subject of research encompassed Al/GFRP fibre metal laminates. Autoclave process has been selected for FML profiles production. The manufacturing process was followed by quality analysis for laminates produced.

The achievement of high stability and dimensional tolerance of thin-walled FML laminates is ensured by developed technology. The values of selected sections angles are significantly limited as a result of forming of FML laminates through the components performing. Failure to adhere to technological recommendations and to high regime of developer technology may lead to the occurrence of defects in FML.

Thin-walled composite structures could be applied in light-weight constructions, such as aircraft structures, which must meet rigorous requirements with regard to operation under complex load. The development of this type of technology may contribute to increased importance of FML sections in research area and finally to increased scope of their applications.

The production of thin-walled FML profiles with complex geometry, which would be characterized by dimensional stability and repeatable structural quality free of defects, is associated with many problems. No studies have been published so far on an effective forming process for FML laminates with complex shapes. Developed methodology has been verified through quality evaluation of produced profiles by means of non-destructive and destructive methods. The development of this type of technology may contribute to increased importance of FML, e.g. in aerospace technology.

Since failure of laminated composites by delaminations is common, the purpose of this paper is to present a numerical procedure to check the stability of delaminations in fiber metal laminate (Glare), with different possible damage configurations, under uni-axial tension. Deformation behavior of the laminate is also examined. Influence of the type and the extent of damage, represented by varying sizes and number of delaminations, on delamination driving force and laminate deformation is found.

Delaminated Glare is modeled by finite element method. Interface cohesive elements are used to model the delaminations. Finite element results provide the deflection/deformation characteristics of the laminate. Driving forces of delaminations are estimated by J integrals that are numerically obtained over cyclic paths near delamination tips. Laminates with different types of delaminations are also fabricated and externally delaminated for measurement of their interlaminar fracture toughness. The delamination is considered to be stable if its driving force is less than corresponding interlaminar fracture toughness of the laminate.

Delaminations are found to be stable in laminates with lower number of delaminations and unstable in laminates with higher number of delaminations. Increase in size of delaminations increases the deformations but reduces the delamination driving force whereas increase in number of delaminations increases both deformations and driving forces. The trends change in case of laminates with symmetrical damage. Shape of delamination is also found to influence the deformations and driving forces. The finite element model is validated.

There is scope for validating the numerical results reported in the paper by theoretical models.

Checking the stability of delaminations and their effect on deformation behavior of the laminate helps is assessment of safety and remaining life of the laminate. If failure is predicted, preemptive action is taken by using repair patch ups at identified critical locations in order to avoid failures in service conditions.

The paper offers the following benefits: use of cohesive zone method that is readily possible in finite element procedures and is relatively simple, fast and reasonably accurate is demonstrated; suitability of using J integrals over paths crossing non-homogeneous and property mismatched material layers is tested; and influence of the type and the extent of damage in the laminate on its deformation behavior and delamination driving forces is found. This type of work has not been reported so far.