Multilayer Delamination Research Articles

Frictional resistance and delamination mechanisms in 2D tungsten diselenide revealed by multi-scale scratch and in-situ observations

Friction phenomena in two-dimensional (2D) materials are conventionally studied at atomic length scales in a few layers using low-load techniques. However, the advancement of 2D materials for semiconductor and electronic applications requires an understanding of friction and delamination at a few micrometers length scale and hundreds of layers. To bridge this gap, the present study investigates frictional resistance and delamination mechanisms in 2D tungsten diselenide (WSe2) at 10 µm length and 100–500 nm depths using an integrated atomic force microscopy (AFM), high-load nanoscratch, and in-situ scanning electron microscopic (SEM) observations. AFM revealed a heterogenous distribution of frictional resistance in a single WSe2 layer originating from surface ripples, with the mean increasing from 8.7 to 79.1 nN as the imposed force increased from 20 to 80 nN. High-load in-situ nano-scratch tests delineated the role of the individual layers in the mechanism of multi-layer delamination under an SEM. Delamination during scratch consists of stick-slip motion with friction force increasing in each successive slip, manifested as increasing slope of lateral force curves with scratch depth from 10.9 to 13.0 (× 103) Nm−1. Delamination is followed by cyclic fracture of WSe2 layers where the puckering effect results in adherence of layers to the nanoscratch probe, increasing the local maximum of lateral force from 89.3 to 205.6 µN. This establishment of the interconnectedness between friction in single-layer and delamination at hundreds of layers harbors the potential for utilizing these materials in semiconductor devices with reduced energy losses and enhanced performance.

Dynamic response of aluminum-graphene layered nanocomposites under shock compression and release based on atomistic simulations

To understand the role of aluminum-graphene (Al-Gr) interface, molecular dynamics simulations have been conducted to investigate the dynamic response of Al-Gr layered nanocomposites. The propagation law of shock waves is revealed and the dislocation nucleation at Al-Gr interface may dominate the plastic deformation mechanism at low impact velocities, which results in the propagation of stepped waveforms. In other words, Gr facilitates dislocation nucleation and its full development in each Al layer. At high impact velocities, Gr can hinder the forward propagation of BCC Al, although Gr can promote BCC nucleation. During shock release, Gr reduces the spall strength of the Al-Gr layered nanocomposites, and then the fracture is dominated by interface fracture, exhibiting single-layer or multi-layer delamination. Gr is found to undergo bending and folding, but Gr remains intact owing to its exceptionally high tensile strength and resistance to high temperatures. With the development of voids and cracks near the Al-Gr interface, the Al layer undergoes significant geometric deformation without internal fragmentation..

Influence of projectile physical state on ballistic energy absorption capacity of UHMWPE laminate: Experiment and simulation

This paper presents the influence of projectile physical state on ballistic energy absorption capacity of UHMWPE laminate. Specifically, standard fragment simulating projectile (FSP) and 7.62 mm × 39 mm mild steel core projectile (MSCP) are utilized to perforate two kinds of areal density laminate. Internal damage morphologies of post-impact laminate are characterized via X-ray computer tomography (CT). A sub-laminate discretization approach was used to establish numerical laminate model, and decoupling parametric studies of projectile state were performed. Results of ballistic tests show that ballistic energy absorption capacity of laminate depends on projectile state and laminate areal density. Multi scale damage morphologies analysis indicate that shear fracture and multi-layer delamination failure are the primary failure modes of post-impact laminate, which were in good agreement with simulation results. Results of parametric studies suggest that high-speed spin of projectile will cause torsional deformation of laminate.

Delamination model of an epoxy-impregnated REBCO superconducting pancake winding

Rare-earth barium copper oxide (REBCO) coated conductor (CC) tapes are promising for high-energy and high-field applications. In epoxy-impregnated REBCO superconducting windings, during the cooling process, the delamination induced by thermal mismatch stress significantly threatens stable operation due to the weak c-axial strength of REBCO CC tapes. In this study, a two-dimensional axisymmetric multilayer delamination finite element model with main layers of REBCO CC tapes and insulation materials was developed based on the bilinear cohesive zone model. Based on the proposed model, the stress distribution and delamination properties of an epoxy-impregnated REBCO winding induced during the cooling process were investigated. Furthermore, the effects on the structural configuration on the delamination and optimisation schemes of fabrication are discussed. The model results indicate that during the cooling process of the REBCO winding, when the radial tensile stress induced by the thermal mismatch stress is greater than the delamination strength, interface cracking will occur. Interface failure occurs in regions containing several turns of coils and not just a single-turn coil. Our analyses indicate that structural failure caused by delamination depends on the radius ratio of the outer to the inner winding, where a small radius ratio is preferred to reduce the risk of delamination. An excessive radius ratio can result in multiple delamination failures during the cooling process. The optimisation scheme, which divides the winding into several sub-windings with a consistently small radius ratio, is an effective method for mitigating the risk of delamination failure, which is consistent with available experimental results. Additionally, by reducing the thermal expansion coefficient of the epoxy resin, the risk of delamination failure during cooling can be significantly reduced. For the winding structure considered in this study, if the coefficient of thermal expansion of the epoxy resin is reduced to 5 ( K−1), then delamination failure caused by thermal mismatch will be eliminated. Our model results are consistent with those of several valuable experimental phenomena and numerical calculated in the literature.

Ripplocations in layered materials: Sublinear scaling and basal climb

The ripplocation is a crystallographic defect which is unique to layered materials, combining nanoscale delamination with the crystallographic slip of a basal dislocation. Here, we have studied basal dislocations and ripplocations, in single and multiple van der Waals layers, using analytical and computational techniques. Expressions for the energetic and structural scaling factors of surface ripplocations are derived, which are in close correspondence to the physics of a classical carpet ruck. Our simulations demonstrate that the lowest-energy structure of dislocation pile-ups in layered materials is the ripplocation, while large dislocation pile-ups in bulk graphite demonstrate multilayer delamination, curvature and voids. This can provide a concise explanation for the large volumetric expansion seen in irradiated graphite.

Characterization of multilayer delaminations in composites using wavenumber analysis: numerical and experimental studies

Delamination is one of the most common and dangerous failure modes for composites because it takes place and grows in the absence of any visible surface damage. The successful implementation of delamination detection in aerospace composite structures is always challenging due to the general anisotropic behavior of composites and multilayer delamination scenarios. This article presents a numerical and experimental investigation to detect and characterize the multilayer delaminations in carbon fiber–reinforced polymer composite plates using guided waves and wavenumber analysis. Multiphysics three-dimensional finite element simulations of the composite plate with five different delamination scenarios are conducted to provide the out-of-plane wave motion for wavenumber analysis. The out-of-plane results from finite element simulations of one delamination and two delaminations are validated by the scanning laser Doppler vibrometer measurements. It is found that the wavenumber analysis can identify the plies between which the delamination occurs and evaluate the delamination severity by comparing the new wavenumbers due to the trapped waves in the delamination regions, which is potentially related to delamination severity. Both numerical and experimental results demonstrate a good capability for the detection and characterization of multilayer delaminations in composite structures.

Micromechanical properties of pyrolytic carbon with interlayer crosslink

Pyrolytic carbon (PyC) materials are laminar deposits formed from the high-temperature pyrolytic reaction of volatile hydrocarbons. The outstanding mechanical performance of PyC renders it attractive as interfacial materials in aerospace applications and thermonuclear fusion. But the deposition process of PyC under extreme conditions in particular makes it challenging to achieve large-sized specimens used in further cognition on processing-microstructure-property relationship for PyC materials. Toward recent molecular insights into the initial formation of PyC [Carbon 148 (2019) 307–316], we herein performed molecular dynamics simulations to investigate the micromechanical properties of PyC with the consideration of interlayer crosslinks. Under out-of-plane uniaxial tension, moderate numbers of interlayer crosslinks can significantly enhance the mechanical properties of PyC. Meanwhile, the increase of interlayer crosslinks will improve the energy dissipation through local and multilayer delamination and tearing. Interlayer crosslinks can provide strong junctions between adjacent layers to bear out-of-plane shear deformation effectively. While under in-plane tension or shearing, the mechanical properties of PyC are weakened due to intralayer pore defects introduced by interlayer crosslinks. Moreover, tension-compression asymmetry of PyC is found at nanoscale. Graphene layers with interlayer crosslinks experience kink-like puckering deformation in the in-plane compression, while they only straighten in the in-plane stretching before failure.

Monolithic Flexible Supercapacitors Integrated into Single Sheets of Paper and Membrane via Vapor Printing.

A novel approach to fabricate supercapacitors (SCs) via vapor printing, specifically oxidative chemical vapor deposition (oCVD), is demonstrated. Compared to stacking multiple layers into a SC, this method enables the monolithic integration of all components into a single-sheet substrate, minimizing the inactive materials and eliminating the possibility of multilayer delamination. Electrodes comprised of pseudocapacitive material, poly(3,4-ethylenedioxythiophene) (PEDOT), are deposited into both sides of a sheet of flexible porous substrate. The film deposition and patterning are achieved in a single step. The oCVD PEDOT penetrates partially into the porous substrate from both surfaces, while leaving the interior of the substrate serving as a separator. Near the surface, the PEDOT coating conforms to the substrate's structure without blocking the pores, resembling the substrate's intrinsic morphology with high surface area. The porously structured PEDOT coating, paired with in situ ion gel electrolyte synthesis, gives enhanced electrode-electrolyte interfaces. The monolithic device demonstrates high volumetric capacitance (11.3 F cm-3 ), energy density (2.98 mWh cm-3 ), and power density (0.42 W cm-3 ). These outstanding performance metrics are attributed to the large loading of active materials, minimization of inactive materials, and good electrode-electrolyte interfaces. SC arrays can be printed on a single substrate without the use of wire interconnects.

Alteration kinetics of natural stones due to sodium sulfate crystallization: can reality match experimental simulations?

Salt decay is a very destructive mechanism that affects frequently the porous building materials of our architectural heritage. Sodium sulfate is one of the salts found in this context. It usually demonstrates high destructive power in salt crystallization tests because it can crystallize not only during evaporative processes but also when the temperature drops or when the salt solution comes into contact with pre-existing crystals. However, the use of extreme temperatures or successive wet/dry cycles also makes these tests unrepresentative of reality. To verify whether sodium sulfate can also be so destructive in field conditions, we have performed crystallization tests consisting of a single isothermal drying event. Three natural stones, relevant for the architectural heritage, were used for the purpose: Bentheimer sandstone, Anca limestone, and a current Portuguese limestone of low porosity. The stones gave rise to distinct salt decay patterns: efflorescence, multilayer delamination and unilayer delamination, respectively. These morphological alterations were characterized at the micrometer scale by a new method based on what we have called the alteration kinetics curve. Such curve is calculated from topographic profiles obtained by a non-contact optical technique. The multilayer and unilayer delamination decay were also monitored by time-lapse photography. The work led us to conclude that sodium sulfate can indeed be also very destructive in field-representative conditions. Moreover, it showed that the optical method can be a valuable aid in the development of more realistic salt crystallization tests.

Impact damage resistance of CFRP with nanoclay-filled epoxy matrix

The influence of nanoclay on the impact damage resistance of carbon fibre–epoxy composites has been investigated using the low-velocity impact and compression after impact (CAI) tests. The load–energy vs. time relations were analyzed to gain insight into the damage behaviours of the materials. The CFRPs containing organoclay brought about significant improvement in impact damage resistance and damage tolerance in the form of smaller damage area, higher residual strength and higher threshold energy level. The presence of nanoclay in the epoxy matrix induced the transition of failure mechanisms of CFRP laminates during the CAI test, from the brittle buckling mode to more ductile, multi-layer delamination mode. Addition of 3 wt% clay was shown to be an optimal content for the highest damage resistance.

Quantitative adhesion measures of multilayer films: Part I. Indentation mechanics

The mechanics for calculating the quantitative driving force of indentation-induced delamination of thin-film multilayers is presented. The solution is based on the mechanics developed by Marshall and Evans [D.B. Marshall and A.G. Evans, J. Appl. Phys. 56, 2632 (1984).] and extended to the general case of a multilayer by use of standard bending and thin-plate analyses. Presented and discussed are the specific solutions for the bilayer case that show that in the limit of zero thickness of either layer, the solution converges to the single-layer case. In the range of finite thickness, the presence of the superlayer increases the driving force relative to that possible for the original film alone and can be optimized to the experimental situation by proper choice of thickness, elastic constants, and residual stress. The companion paper “Quantitative adhesion measures of multilayer films: Part II. Indentation of W/Cu, W/W, Cr/W” discusses experimental results with copper, tungsten, and chromium thin films.

Thermally induced delamination of multilayers

Steady-state delamination of multilayered structures, caused by stresses arising during processing due to thermal expansion mismatch, is analyzed by a fracture mechanics model based on laminate theory. It is found that inserting just a few interlayers with intermediate thermal expansion coefficients may be an effective way of reducing the delamination energy release rate. Uneven layer thicknesses and increasing elastic mismatch are shown to raise the energy release rate. Experimental work confirms important trends of the model.