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Polymer composite materials (PCMs) can sustain themselves in harsh environments without suffering any loss of properties of the constituents. The present study focussed on erosion wear behavior of step-wise layered polymer composite materials (LPCMs). Samples were fabricated with epoxy as matrix and aluminum as filler particles using hand lay-up technique. Volume fraction of the filler was varied at four different layers along the direction thickness. Experiments were conducted at room temperature using angular shaped silica sand erodent impacting at 151 m/s and at impingement angles of 30°, 45°, 60° and 90°. Due to the variation in filler content, testing of samples was performed at two different orientations: i) top to bottom (T-B) and ii) bottom to top (B-T). The increased filler content reduced the erosion wear as tested from B-T, while a reverse trend was observed along T-B. Moreover, erosion wear was found to be higher at 45° impingement angle indicating the semi-ductile nature of LPCMs. At this angle, the erosion wear rate at top layer was 76.47% lower compared to bottom due to the presence of high filler content.

It is apparent that well-designed functionally graded materials (FGMs) exhibit smooth transition in properties. In this paper, polymer based functionally graded composite materials (FGCMs) were developed in combination with copper (Cu) particles and epoxy. A novel stepped layer configuration through a curing-phase approach at each layer in three different curing conditions (C1, C2, C3) have been processed. A significant enhancement in mechanical strength and erosion resistance was observed at higher curing temperatures (60°C) for sample C3. The results indicated tensile and compressive strengths of C3 enhanced by 40.20%, 17.48% and 20.18%, 9.74% compared to C1 and C2, respectively. Furthermore, when the FGM is loaded from top to bottom (T-B), there is an enhancement in flexural strength of C3 by 7.88% when compared to bottom to top (B-T) loading. In addition, the erosion wear of C3 was found to be lowest of all the samples.

The novel reactive methylmethacrylate (MMA) thermoplastic resin (commercially known as Elium® resin) is the first liquid thermoplastic resin which is curable at room temperature. This resin is a competitive solution against traditional epoxy-based composites. In this work, novel non-crimp (NC) glass fabric/MMA resin composites were manufactured using a vacuum infusion process. Cellulose microcrystals (CMCs) were dispersed in the resin to improve the fibre/matrix interface and the composite properties. CMCs were first dispersed in the resin using an ultrasonication process and then the CMC/MMA resin suspension, mixed with a peroxide initiator, was infused into the reinforcing fabric. The amounts of CMCs dispersed in the resin were 0.5%, 1% and 2% (of the weight of the resin). The influence of CMCs on the interlaminar shear strength (interface), flexural properties, abrasive wear and dynamic-mechanical behaviour was thoroughly investigated. From the mechanical characterisation, it was observed that the addition of 1% CMC to the NC glass/MMA resin composites improved the flexural strength, interlaminar shear strength and wear performance by 30.77%, 38.04% and 22.27%, respectively as compared to the neat glass/MMA resin composite. Above this amount of CMC (i.e., 1 wt%), the properties started to degrade as a result of CMC agglomeration.

Elium® is a novel liquid Methylmethacrylate thermoplastic (TP) matrix that can be cured at room temperature. Elium® resin provides the properties of TP polymer composites and is a competitive alternative to epoxy-based composites. In this work, a quadriaxial non-crimp (NC) glass fabric/Elium® based polymer composites were manufactured using vacuum assisted resin transfer moulding (VaRTM). The static mechanical properties of these composites were evaluated under the tensile and flexural loads. Further, interfacial properties like interlaminar shear strength (ILSS) and fracture toughness (Mode-I and Mode-II) were characterised. To study the influence of ageing on the mechanical properties of glass fabric/Elium® (GF/E) based composites, the test samples were aged in distilled water at a temperature of 60°C for 60 days. The obtained mechanical properties were compared between dry samples (control) and post-water immersed (aged) samples. It was found that water ageing degraded the properties of tensile, flexural strength, ILSS and Mode-II toughness by 30%, 59%, 46%, 37%, respectively. On the contrary, Mode-I fracture toughness of aged samples was 90% higher, indicating significant fibre bridging due to ageing. The microscopy and scanning electron microscopy (SEM) revealed significant failure as the degradation of fibre/matrix interface due to hygrothermal ageing. The overall performance of GF/E composites with infusible TP resin is sensitive to hygrothermal ageing.

The present study reports the mechanical performance of polytetrafluoroethylene (PTFE) coated fabrics. Glass fabrics with two weave structures, three dimensional plain-woven knitted (3D) and satin weave (SW) were tested. These fabrics were coated with PTFE in different weight percentages (30% and 60%). Mechanical tests included uniaxial tensile, tear (double tongue and pendulum tear), puncture, yarn pull-out and low-velocity impact (LVI) tests. The influence of weave pattern and PTFE coating on these mechanical properties was investigated. In the case of yarn pull-out and tensile tests, 60% PTFE coated glass fabrics exhibited better performance due to the increased adhesive bonding and inter-yarn friction. However, the 30% PTFE coated glass fabrics exhibited better performance for tear, puncture, and LVI tests. The SW fabrics exhibited superior performance to the 3D fabrics in all the mechanical tests performed. Overall, the results indicate that SW fabrics offer better mechanical performance than 3D fabrics under different loading conditions. In terms of coating percentage, 30% PTFE coated fabrics exhibited better mechanical performance than the 60% coated ones.

peer-reviewed The full text of this article will not be available in ULIR until the embargo expires on the 30/05/2022 Laser-assisted automated tape placement (LATP) in-situ consolidation of thermoplastic composites offers an efficient solution for production of large, high performance composite structures. The present work investigates laser repass treatment as a method of enhancing surface roughness and mechanical properties of LATP processed CF/PEEK laminates. Three laminate stacking sequences were studied, viz. [0°]16, [−45°/0°/45°/90°]2s and [±45°]4s. Four repass treatments were performed, including single, double, perpendicular and tool-side repasses. The effect of these repasses on interlaminar shear strength (ILSS), open-hole compression (OHC), in-plane shear (IPS), density, fibre volume fraction, void content and surface roughness was investigated. Surface roughness tests confirmed the improvement of the surface finish due to repass treatment. However, insignificant differences in ILSS values were observed across all repass treatments, but a single laser repass did appear to improve the OHC and IPS performance. Autoclave treated samples were used as a benchmark to compare with LATP processed laminate properties.

In the present work, dynamic compression response of polypropylene (PP) based composites reinforced with Kevlar/Basalt fabrics was investigated. Two homogeneous fabrics with Kevlar (K3D) and Basalt (B3D) yarns and one hybrid (H3D) fabric with a combination of Kevlar/Basalt yarns were produced. The architecture of the fabrics was three-dimensional angle-interlock (3D-A). Three different composite laminates were manufactured using vacuum-assisted compression molding technique. The high strain rate compression loading was applied using a Split-Hopkinson Pressure Bar (SHPB) set-up at a strain rate regime of 3633–5235/s. The results indicated that the dynamic compression properties of thermoplastic 3D-A composites are strain rate sensitive. In all the composites, the peak stress, toughness and modulus were increased with strain rate. However, the strain at peak stress of Basalt reinforced composites (B3D, H3D) decreased approximately by 25%, while for K3D specimens it increased approximately by 15%. The K3D composites had a higher strain rate as compared to the B3D and H3D composites. In the case of K3D composite, except strain at peak stress, remaining dynamic properties were lower than the B3D composite, however, hybridization increased these properties. The failure mechanisms of 3D-A composites were characterized through macroscopic and scanning electron microscopy (SEM).

This paper investigates the characterization of in-plane shear properties of thermoplastic composites reinforced with Kevlar/basalt fabrics. Different fabrics had architectures of two dimensional plain woven (2D-P) and three dimensional angle-interlock (3D-A). Intralayer hybridization was performed during the weaving of the fabrics with the combination of Kevlar and basalt yarns. Five 2D-P and three 3D-A composite laminates were manufactured with polypropylene (PP) as a matrix, using compression molding. Iosipescu shear tests were carried out to evaluate the in-plane shear properties. The experimental results revealed that the shear properties including shear modulus, shear strength and shear failure strain of homogeneous composites were improved by 6.5–14.9%, 4.3–19.7%, and 3.2–46.7%, respectively. Similarly, change in the fabric architecture from 2D-P to 3D-A also enhanced the shear strength and shear failure strain by 32.0–41.6% and 7.2–22.5%, respectively. Intralayer hybrid composites had better in-plane shear properties than the interlayer hybrid composites. The fracture morphologies of the specimens were examined by scanning electron microscopy (SEM).

This paper presented an experimental and numerical investigation on the low velocity impact response of thermoplastic hybrid composites reinforced with Kevlar/basalt fabrics. Two hybrid and one Kevlar homogeneous composite laminates were manufactured with polypropylene as a resin. In the hybrid composites, one hybrid composite (H-1) was manufactured with alternate stacking of four layers of basalt and four layers of Kevlar and the second hybrid composite (H-2) was manufactured with four Kevlar layers on front face and four basalt layers on back face. Low velocity impact tests were performed using a drop-weight impact equipment at three different energies (25 J, 50 J and 75 J). Among the two hybrid composites H-1 hybrid composite exhibited 15.58–20.79% and 13.47–20.47% improvement in the peak force and energy absorption, respectively, than the H-2 hybrid composite. The peak force and energy absorption of Kevlar homogeneous composite was also improved by 10.07–14.37% and 5.38–11.29%, respectively, due to hybridization. A three dimensional (3D) dynamic finite element software, Abaqus/Explicit, was implemented to simulate the experimental results of low velocity impact tests. A user-defined material subroutine (VUMAT) based on Chang-Chang linear-orthotropic damage model was implemented into the finite element code. The predictions from numerical simulation were found to be in good agreement with the experimental results.

The present study compared the tensile and low velocity impact (LVI) response of Kevlar/basalt fabrics. Homogeneous and hybrid fabrics with structures of two dimensional plain woven (2D-P) and three dimensional angle-interlock (3D-A) were woven with Kevlar and basalt yarns. Interlacing of brittle basalt yarns with high-ductility/high-toughness Kevlar yarns enhanced the tensile strength of 2D-P fabrics by 5.39–50.29% and 3D-A fabrics by 14.80%. Similarly hybridization enhanced the energy absorption of 2D-P fabrics by 8.58–37.71% and 3D-A fabrics by 13.45–20.14%. Change in the architecture from 2D-P to 3D-A also enhanced the tensile and impact resistance of fabrics. Different failure modes induced due to tensile and LVI loads were identified.

Ballistic performance of hybrid thermoplastic composite armors reinforced with Kevlar and basalt fabrics of 2D plain woven (2D-P) and 3D angle interlock (3D-A) architectures was investigated through experiments and simulations. Two types of hybrid armors were manufactured with polypropylene (PP) as a matrix: one with a non-symmetric (H-1) stacking sequence and the other with a symmetric (H-2) stacking sequence. Ballistic impact tests were imparted with a 9 mm full metal jacket (FMJ) projectile on the H-1 and H-2 armors. H-1 armor exhibited full perforations for the velocities between 365 and 395 m/s, while the H-2 armor was able to confront successfully. The front face damage of the armor was not influenced by the stacking sequence. The ballistic limit was increased by 26.27% from H-1 armor to H-2 armor, indicating the influence of placing 3D-A fabrics on the front face. However, the overall stacking sequence showed a significant influence on the overall ballistic performance of composite armors.

The objective of the present study is to investigate the ballistic impact behavior of Kevlar/Polypropylene (PP) composites through hydrocode simulations performed in ANSYS AUTODYN-2D/3D. The studies are carried out based on the experimental and numerical investigation of ballistic impact response of Kevlar/PP composites reported in our recent work [Bandaru et al. Ballistic impact response of Kevlar ® reinforced thermoplastic composite armors, Int J Impact Eng 2016;89:1-13]. The interface between the Kevlar and PP matrix is improved by adding polypropylene grafted with Maleic anhydride. The numerical model is validated by evaluating the ballistic impact performance of Kevlar/PP composites when impacted with STANAG-2920 fragment simulating projectile (FSP). Kevlar/PP showed improved ballistic impact performance than that of the Kevlar/Vinylester composite reported in the literature. Numerical simulations are further extended to study the influence of the mass of the projectile on the ballistic impact performance of Kevlar/PP composite armors in terms of ballistic limit, energy absorption and residual velocity. It is observed that shear plugging is the dominant failure mechanism in thermoplastic composites.

In this study, mechanical behavior of thermoplastic composites reinforced with two-dimensional plain woven homogeneous and hybrid fabrics of Kevlar/basalt yarns was studied. Five types (two homogeneous and three hybrids) of composite laminates were manufactured using compression molding technique with polypropylene (PP) resin. Static tensile and in-plane compression tests were carried out to evaluate the mechanical properties of the laminates. The tension and in-plane compression tests had shown that the composites with the combination of Kevlar and basalt yarns present better tensile and in-plane compressive behavior as compared to their base composites. Improvement in the properties such as elastic modulus, strength and failure strain in both tension and in-plane compression was observed due to the hybridization. Numerical simulations were performed in ABAQUS/Standard by implementing a user-defined material subroutine (VUMAT) based on Chang-Chang criteria. Good agreement between the experimental and numerical simulations was achieved in terms of damage patterns.

The present work reported the mechanical characterization of novel polypropylene (PP) composites reinforced with three-dimensional angle-interlock (3D-A) Kevlar/basalt fabrics. Two homogeneous fabrics with Kevlar (K3D) and basalt yarns (B3D), and a hybrid fabric (H3D) with a combination of both Kevlar and basalt yarns were produced. Three types of two layer 3D-A composites were manufactured using vacuum-assisted compression molding method. Static tensile and in-plane compression tests were carried out on the manufactured composites. The mechanical behavior of the three 3D-A composites was compared in terms of stress-strain response, elastic modulus, strength and failure strain. Influence of hybridization on the mechanical behavior of the 3D-A composites was also studied. Significant improvement in the tensile behavior of 3D-A homogeneous composites was observed due to hybridization. Meanwhile, there was no considerable improvement in in-plane compression behavior. The damage patterns for in-plane compression loading were examined through scanning electron microscopy (SEM) to explore the possible damage patterns such as matrix cracking, fiber failure, delamination and deformation. Numerical simulations were carried out using ABAQUS/Standard, by implementing a user-defined material subroutine (VUMAT) based on the Chang-Chang linear orthotropic damage model. Good agreement between experimental and numerical simulations was achieved in terms of damage patterns.

In this study, low velocity impact (LVI) behaviors of composite laminates reinforced with fabrics of different architecture are investigated. Three kinds of fabric architecture, namely, two-dimensional plain woven (2D-P), three-dimensional orthogonal (3D-O) and three-dimensional angle interlock (3D-A), are prepared with Kevlar 29 (Kevlar) yarns. Composite laminates are manufactured with Kevlar fabrics and polypropylene (PP) resin. These composites are impact tested at 4 m/s and 6 m/s impact velocities. The post-impact response of the composites of different fabric architecture is studied. The results revealed that the impact resistance is mainly dependent on the in-plane stiffness of the laminates. The energy absorption ability is predominantly influenced by the existence of yarns in the thickness direction. The 3D composites absorbed 14–26% higher energy than the 2D laminates. Especially, 3D-A laminates exhibited a higher peak load (14.21–30.25%), more energy absorption (12.7–26.2%) and lower cone formation at the back of the target (25–39%) as compared to 3D-O and 2D-P composites.

A constitutive model based on the concept of continuum damage mechanics has been proposed to study the progressive damage behavior of composite laminates under ballistic impact. The proposed model is investigated in five steps: First, the quadratic form of damage initiation criteria are presented to predict the initiation of failure in different modes. Second, an exponential form damage evolution law combined with characteristic length based fracture energy approach has been presented. Stiffness degradation is characterized by a variable determined by the equivalent displacement for each failure mode. Third, an experimentally verified strain rate model that considers the rate dependency of the strength and modulus of the composite laminate is considered. Fourth, cohesive elements are inserted at every inter-layer for modeling the delamination evolution. Fifth, the constitutive model has been combined with an element erosion algorithm for the removal of highly distorted elements. Simulations have been performed using reduced integration hexahedra elements (RIHE) and full integration hexahedra elements (FIHE). Implementation of cohesive elements exhibited better delamination progression. Experimentally verified strain rate model enhanced the efficiency of the model showing good correlation between the present simulations and experimental observations, in terms of damage patterns, residual velocity, kinetic energy and ballistic limit.

In this study, experimental investigations on Kevlar fiber reinforced polypropylene (PP) woven composites under high strain rate compression loading are discussed. Kevlar/PP composite laminates with 8 and 24 layers are fabricated using vacuum assisted compression molding technique. Maleic anhydride grafted-PP (MAg-PP) is added to PP to improve the interfacial property between Kevlar fiber and PP resin. The through-thickness properties at high strain rates from 1370 to 6066 s−1 are obtained using split Hopkinson pressure bar (SHPB) setup. The behavior of PP resin is found to be different than the commonly used thermoset resins, such as epoxy. Dynamic stress–strain relations are drawn to reveal the mechanical properties at high strain rates and these relations appear to be rate sensitive. As a result, the peak stress increased by three times, toughness increased by almost ten times and strain at peak stress increased by as much as two times with an increase in the strain rate. The final failure of the specimens is examined by scanning electron microscopy (SEM) to explore the possible failure mechanisms such as, delamination, fiber failure and shear fracture.

The ballistic impact response of thermoplastic-based composite armors made from Kevlar ® fabric and polypropylene (PP) matrix has been investigated against ballistic test standard NIJ-STD 0106.01 Type IIIA. Kevlar ® fabrics of different architectures, namely 2D plain woven, 3D orthogonal and 3D angle interlock fabrics, were produced and used as reinforcements to fabricate composite armor panels, using compression molding technology. Interfacial property between PP and Kevlar ® was improved by adding a coupling agent called maleic anhydride grafted PP. Reduced density was observed in Kevlar ® thermoplastic-based composites as compared to that of the thermoset-based laminates. Ballistic impact tests were imparted with 9 mm full metal jacket (FMJ) on armor panels having different fabric architecture. Ballistic test results revealed that 2D armor was 2.4–7% more susceptible to damage than 3D armors. Hydrocode simulations were carried out using ANSYS AUTODYN v. 14.0 to obtain an estimate for the ballistic limit velocity and simulate failure modes. Post-impact damage patterns obtained from the simulations were compared with the experimental results to assess the performance of the simulations. Good correlation between the hydrocode simulations and experiments was found, both in terms of failure modes and damage patterns. 3D composite armors were able to confront the 9 mm FMJ projectile; however, the 2D plain woven armors failed. The increase in the ballistic limit from 2D plain woven armor to 3D orthogonal and 3D angle interlock armors was 16.44% and 20%, respectively, indicating the effect of fabric architecture.

The present study evaluates the influence of hybridization on the interlaminar shear and abrasive wear properties of composites manufactured with polytetrafluoroethylene (PTFE) coated glass fabrics. Homogeneous composites were manufactured using two dimensional plain woven (2D), three dimensional knitted (3D) and satin weave (SW) fabrics. Hybrid composites were manufactured with the same fabrics and a steel metal mesh (MM) stacked on the top and bottom of the laminates. The interfacial property was obtained through interlaminar shear strength (ILSS) tests. Abrasive wear tests were performed against a silicon carbide (SiC) paper of grit size 120 μm using a plate on plate apparatus. Loads ranging from 10 N to 50 N were applied at an interval of 10 N with a speed of 10 rad/s. Incorporation of MM influenced the physical properties like thickness, density and void content. Hybridization of homogeneous composites with MM improved the ILSS by 56%, 10% and 18% for 2D, 3D and SW composites, respectively. All the hybrid composites showed better wear performance in terms of coefficient of friction (COF) and specific wear rate (K0). SW and SW-MM composites exhibited better wear performance in all the wear properties as compared to the 2D, 2D-MM, 3D and 3D-MM composites. Scanning electron microscopy (SEM) revealed that the bonding between fibre and matrix could be improved in the case of 2D and 2D-MM composites.

In the present study, effect of hybridization on the hybrid composite armors under ballistic impact is investigated using hydrocode simulations. The hybrid composite armor is constructed using various combinations and stacking sequences of fiber reinforced composites having woven form of fibers specifically high specific-modulus/high specific-strength Kevlar fiber (KF), tough, high strain-to-failure fiber Glass fiber (GF) and high strength/high stiffness Carbon fiber (CF). Different combinations of composite armors studied are KF layer in GF laminate, GF layer in KF laminate, KF layer in CF laminate and CF layer in KF laminate at various positions of hybridized layers for a fixed thickness of the target. In this article the results obtained from the finite element model are validated for the case of KF layer in a GF laminate with experimental predictions reported in the literature in terms of energy absorption and residual velocity and good agreement is observed. Further, the effect of stacking sequence, projectile geometry and target thickness on the ballistic limit velocity, energy absorbed by the target and the residual velocity are presented for different combinations of hybrid composite armors. The simulations show that, at a fixed thickness of the hybrid composite armor, stacking sequence of hybridized layer shows significant effect on the ballistic performance. The results also indicate energy absorption and ballistic limit velocity are sensitive to projectile geometry. Specifically, it is found that arranging the KF layer at the rear side, GF layer in the exterior and CF layer on the front side offers good ballistic impact resistance. The hybrid composite armor consisting of a CF layer in KF laminate acquires maximum impact resistance and is the best choice for the design compared to that of other combinations studied.

In the present study, abrasive wear tests were conducted to investigate the effect of hygrothermal ageing on the friction and wear resistance of glass/Polytetrafluoroethylene (PTFE) composites. Non-hybrid and hybrid composites were manufactured with PTFE coated two-dimensional plain weave (2D), three-dimensional knitted (3D), satin weave (SW) fabrics and a steel metal mesh (MM). Hybrid composites were manufactured with PTFE coated glass fabrics and MM by placing it on the top and bottom of the laminate. Specimens were aged in a distilled water at a temperature of 35 °C for 60 days. Abrasive wear tests were performed with 120 μm grit silicon carbide (SiC) paper using a plate on plate apparatus with loads ranging between 10 N and 50 N. Water absorption and kinetic parameters were determined and Fickian diffusion behaviour was observed. Differential Scanning Calorimetry (DSC) analysis showed that the crystallinity was sensitive to the hygrothermal ageing and decreased with an increase in water uptake. Hygrothermal ageing reduced the abrasive wear resistance of both the non-hybrid and hybrid composites as compared to the non-aged ones. For the same ageing conditions, the inclusion of MM improved the wear resistance of non-hybrid composites.

peer-reviewed The present study deals with the quasi-static and high strain rate characterization of Kevlar-129 based thermoplastic composites. Two different thermoplastic matrices, namely, Polypropylene (PP) and Polyetherimide (PEI) were used to manufacture composite laminates. Quasi-static compression tests were performed at strain rates of 0.041 s−1 and 0.045 s−1. High strain rate tests were performed using a split Hopkinson pressure bar apparatus within the strain rates ranging from 2548 s−1 to 4379 s−1. Stress-strain relations reveals the rate-sensitive behaviour of composites. Kevlar/PP (K-PP) showed higher peak stress under quasi-static loading as compared to the high strain rate test. Comparable peak stresses were revealed under quasi-static and high strain rate loading for Kevlar/PEI (K-PEI) composite. Also, high strain rate compression properties such as peak stress, peak strain and toughness of K-PP were 25%, 27% and 6% higher than that of the K-PEI composite. The failure mechanisms of both the composites were characterized through macroscopic and scanning electron microscopy. K-PP failed majorly due to matrix crush and fibre failure while K-PEI failed due to shear cracking. Damage study reveals that a single fibre based composite system can be tailored to act as an energy-absorbing or dissipating material system by varying the thermoplastic matrix materials

peer-reviewed In this study, the influence of hybridization on the compression response of thermoplastic matrix-based composites under high strain rate loading was investigated. The intra-ply and inter-ply hybrid composites were manufactured with Kevlar/Basalt yarns as the reinforcements with Polypropylene as a matrix. Cylindrical composite specimens were laser cut from the flat compression moulded laminates. The composite specimens were loaded under high strain rate using split-Hopkinson pressure bar setup at strain rates ranging from 2815/s to 5481/s. The study revealed differences in the rate-dependent growth of peak stress, peak strain and toughness with the strain rate. Intra-ply hybrid composites with alternate weaving of Kevlar and basalt yarns exhibited highest peak stress as compared to the Inter-ply hybrid composites (alternate layers of Kevlar and basalt fabrics) and another intra-ply composite containing Kevlar in the warp and basalt in the weft direction. Whereas in inter-ply hybrid composite, with Kevlar as the loading face attained higher stress, while composite with Basalt as the loading face attained higher strain. SEM micrographs revealed that Kevlar on the loading face can bear the impact with lesser delamination as compared to the Basalt on the loading face. Damage studies revealed that Kevlar fiber surface loading results in higher stress as compared to basalt (brittle) surface loading with lower overall damage. PUBLISHED peer-reviewed