Autonomic healing of low-velocity impact damage in fiber-reinforced composites

In this study autonomic self-healing of impact damage in composite materials is shown using a microencapsulated healing agent. The components for self-healing, urea–formaldehyde microcapsules containing dicyclopentadiene (DCPD) liquid healing agent and paraffin wax microspheres containing 10 wt% Grubbs’ catalyst, have been successfully incorporated in a woven S2-glass-reinforced epoxy composite. Low-velocity impact tests reveal that the self-healing composite panels are able to autonomically repair impact damage. Fluorescent labeling of damage combined with image processing shows that total crack length per imaged cross-section is reduced by 51% after self-healing. A testing protocol based on compression after impact reveals significant recovery of residual compressive strength (RCS) in self-healing panels. Self-healing panels show a higher threshold impact energy before RCS reduction, and as impact energy increases, RCS recovery decreases. Qualitative inspection shows that crack separation increases with increasing impact energy, indicating that self-healing performance depends on the ability to adequately fill damage volume.     

Self-healing of delamination cracks in mendable epoxy matrix laminates using poly[ethylene-co-(methacrylic acid)] thermoplastic

This paper investigates the self-healing repair of delamination cracks in a carbon fibre–epoxy laminate using the mendable thermoplastic poly[ethylene-co-(methacrylic acid)] (EMAA). The effects of different types (fibres or particles) and concentrations of the mendable EMAA agent on the self-healing efficiency was measured using mode I interlaminar fracture toughness testing and fractographic analysis. The EMAA was effective in healing delamination damage and increasing the fracture toughness compared to the original laminate. High healing efficiency was achieved by the wide area flow of EMAA (increase of ～25 times) through delamination cracks under the pressure delivery mechanism. High recovery in the fracture toughness was achieved after healing by the formation of large-scale EMAA-bridging ligaments along the delamination, which is a toughening mechanism unique to this type of self-healing material. EMAA proved effective for the multiple repairs of delamination cracks with some loss in the self-healing efficiency of the mendable laminates.     

Interlaminar fracture of CF/EP composite containing a dual-component microencapsulated self-healant

We present an experimental study of the self-healing ability of carbon fibre/epoxy (CF/EP) composite laminates with microencapsulated epoxy and its hardener (mercaptan) as a healing agent. Epoxy- and hardener-loaded microcapsules (average size large: 123 μm; small: 65 μm) were prepared by in situ polymerisation in an oil-in-water emulsion and were dry-dispersed at the ratio 1:1 on the surface of unidirectional carbon fabric layer. The CF/EP laminates were fabricated using a vacuum-assisted resin infusion (VARI) process. Width-tapered double cantilever beam (WTDCB) specimens were used to measure mode-I interlaminar fracture toughness of the CF/EP composites with a pre-crack in the centre plane where the microcapsules were placed. Incorporation of the dual-component healant stored in the fragile microcapsules provided the laminates with healing capability on delamination damage by recovering as much as 80% of its fracture toughness. It was also observed that the recovery of fracture toughness was directly correlated with the amount of healant covering the fracture plane, with the highest healing efficiency obtained for the laminate with large capsules.     

Review of current strategies to induce self-healing behaviour in fibre reinforced polymer based composites

Abstract

This paper addresses the various strategies to induce self-healing behaviour in fibre reinforced polymer based composites. A distinction is made between the extrinsic and intrinsic healing strategies. These strategies can be applied at the level of the fibre, the fibre/matrix interface or at the level of the matrix. It is shown that the degree of healing depends on the type of damage and the testing mode used and examples are given both for extrinsic and for intrinsic healing systems. The conclusion is drawn that self-healing in fibre reinforced composites is possible yet unlikely to become a commercial reality in the near future.     

Effect of self-healing on strength and durability of zeolite-immobilized bacterial cementitious mortar composites

There is a compelling economic incentive to develop concrete materials that can repair its own damage, increase durability and prevent structural failure. This research investigated the potential of adding two different mineral producing bacteria into two types of cementitious mortar matrix to enhance self-healing ability for autonomous crack repair. In this study, zeolite was used as a carrier material to protect bacteria in high pH environment normally exists in concrete. The spore forming ability and ureolytic activity of zeolite-immobilized bacteria were investigated in order to examine potential for producing healing compounds. The self-healing ability of bacteria incorporated normal and fiber reinforced mortars was judged based on the development of compressive strength and permeation properties of cracked specimens with age as well as micro-structural characterization of crack healing compounds using scanning electron microscopy (SEM), energy dispersive spectrometer (EDS) and X-ray diffraction.     

本征型自修复高聚物粘结炸药的制备与损伤愈合性能

为减轻高聚物粘结炸药(PBX)由于力、热等环境因素所产生的微裂纹等损伤对于其性能与使用寿命的影响,根据颗粒填充高分子复合材料的结构特性,设计合成了含DA键的本征型自修复高聚物粘结剂,以期实现PBX内部损伤的自主修复。研究结果表明,采用含可逆DA共价键的TAPE-DAPU为粘结剂,设计制备的PBX材料具有较强的损伤愈合能力,当损伤较轻时,该PBX的强度恢复率超过95%,对于较严重的贯穿性损伤,其修复效率也在65%以上。      

Toughening and self-healing of epoxy matrix laminates using mendable polymer stitching

This paper presents an experimental study into a new type of stitched fibre–polymer laminate that combines high interlaminar toughness with self-healing repair of delamination damage. Poly(ethylene-co-methacrylic acid) (EMAA) filaments were stitched into carbon fibre/epoxy laminate to create a three-dimensional self-healing fibre system that also provides high fracture toughness. Double cantilever beam testing revealed that the stitched EMAA fibres increased the mode I interlaminar fracture toughness (by ∼120%) of the laminate, and this reduced the amount of delamination damage that must subsequently be repaired by the self-healing stitches. The 3D stitched network was effective in delivering self-healing EMAA material extracted from the stitches into the damaged region, and this resulted in high recovery in the delamination fracture toughness (∼150% compared to the original material). The new self-healing stitching method provides high toughness which resists delamination growth while also having the functionality to repeatedly repair multiple layers of damage in epoxy matrix laminates.     

Interlayer self-healing and toughening of carbon fibre/epoxy composites using copolymer films

This paper presents an investigation of the combined self-healing and toughening performance of two copolymers: thermoplastic poly(ethylene-co-methyl acrylate) (EMA) and poly(ethylene-co-methacrylic acid) (EMAA). Carbon fibre composites were manufactured from unidirectional prepregs with rectangular-shaped patches being placed between composite plies. Results from double-cantilever-beam and short-beam-shear testing show that the incorporation of mendable polymers improves interlaminar fracture toughness but causes a reduction in interlaminar shear strength. The healing efficiency in terms of restoration of the interlaminate fracture energy scales linearly with the areal percentage of self-healing material. Microstructure study revealed distinct difference in the fracture surfaces of composites with EMA and EMAA, with EMA displaying extensive nano-scale porous structures in contrast to the more homogenous single phase structure from EMAA.     

The investigation of the effect of particle size on wear performance of AA7075/Al2O3 composites using statistical analysis and different machine learning methods

In this study, 7075 - Al₂O₃ (5 wt%) composites with a particle size of 0.3 µm, 2 µm, and 15 µm were developed by hot pressing. The dry sliding wear performance of the specimens was evaluated under loads of 5 N, 10 N, 20 N, 30 N, and at sliding speeds of 80 mm/s, 110 mm/s, 140 mm/s by reciprocating wear tests. The wear tests showed that 7075 - 5Al₂O₃ (15 µm) exhibited the best wear performance. The volume loss of 7075 - 5Al₂O₃ (15 µm) under load of 30 N for sliding speed of 140 mm/s was 37.1% lower than the unreinforced 7075 alloy. The volume loss (mm³) of composites reinforced with the particle size of 0.3 µm, 2 µm, and 15 µm was 11.62, 9.87, and 8.07, respectively, for load of 30 N and sliding speed of 140 mm/s. An increase in the applied load and sliding speed increased the wear severity by changing the wear mechanism from abrasion to delamination. The analysis of variance (ANOVA) showed that the load was the most significant parameter on the volume loss. The linear regression (LR), support vector regression (SVR), artificial neural network (ANN), and extreme learning machine (ELM) were used for the prediction of volume loss. The determination coefficient (R²) of the LR, SVR, ANN, and ELM was 0.814, 0.976, 0.935, and 0.989, respectively. The ELM model has the highest success. Thus, the ELM model has significant potential for the prediction of wear behaviour for Al matrix composites.     

Self-healing property of epoxy/nanoclay nanocomposite using poly(ethylene-co-methacrylic acid) agent

This paper investigates the self-healing repair of cracks in an epoxy/nanoclay nanocomposite using mendable poly[ethylene-co-methacrylic acid] (EMAA) particles. The effects of two different concentrations of EMAA agent on the self-healing efficiency were measured using single edge notch bar (SENB) testing. Inclusion of EMAA particles into the nanocomposite results an increase in the fracture strength and strain of the SENB specimens. Damaged SENBs were healed at 150 °C for 30 min to achieve up to 63% recovery in critical stress intensity and over 85% recovery in sustainable peak load. Also, X-ray diffraction (XRD) analysis and tensile test used in order to examine the nanocomposite structure and investigate the effects of EMAA inclusion on the nanocomposite mechanical properties. The pressure delivery mechanism of the healing agent is shown by scanning electron microscopy (SEM) images. It seems EMAA can be used as an effective self-healing agent for epoxy/nanoclay nanocomposites.     

Self-repair of structural and functional composites with intrinsically self-healing polymer matrices: A review

Self-healing is a smart and promising way to make materials more reliable and longer lasting. In the case of structural or functional composites based on a polymer matrix, very often mechanical damage in the polymer matrix or debonding at the matrix–filler interface is responsible for the decrease in intended properties. This review describes the healing behavior in structural and functional polymer composites with a so-called intrinsically self-healing polymer as the continuous matrix. A clear similarity in the healing of structural and functional properties is demonstrated which can ultimately lead to the design of polymer composites that autonomously restore multiple properties using the same self-healing mechanism.     

Quantification of chemical and biological calcium carbonate precipitation: Performance of self-healing in reinforced mortar containing chemical admixtures

Cracks increase permeability affecting the durability of concrete. As they develop gradually, it is difficult to determine when to repair them. Self-healing materials can repair themselves gradually as cracks form. In this study, the isolated and combined effect of two self-healing agents for concrete, both based on calcium carbonate precipitation, was studied. Lightweight aggregates were impregnated with chemical and biological solution to be added as healing agents in concrete mixtures. The influence of two common chemical admixtures on the performance of the self-healing agents was also studied. All self-healing agents were able to seal cracks between 0.08 and 0.22 mm in width. The estimated effect of chemical agents on the mean healing was higher than that of biological agents. In addition, thermogravimetric analysis suggests the precipitates are different. Admixtures had no significant influence on the performance of self-healing agents.     

Bulk growth of polycrystalline indium phosphide

The growth of polycrystalline indium phosphide of different grain sizes varying from 15μm to 4000μm has been discussed. The materials have been characterized by a variety of methods including electrical and optical techniques. Device application of the InP prepared was demonstrated by the fabrication of Ag Schottky diodes andp ⁺-n junction using Zn diffusion. The variation of mobility with varying grain size has been determined experimentally and the results interpreted taking into account the effect of compensation.     

Mechanical properties of a self-healing fibre reinforced epoxy composites

Inspired by biological systems in which damage triggers an autonomic healing response, a polymer composite material that can heal itself when cracked has been developed. In this work, compression and tensile properties of a self-healed fibre reinforced epoxy composites were investigated. Microencapsulated epoxy and mercaptan healing agents were incorporated into a glass fibre reinforced epoxy matrix to produce a polymer composite capable of self-healing. The self-repair microcapsules in the epoxy resin would break as a result of microcrack expansion in the matrix, and letting out the strong repair agent to recover the mechanical strength with a relative healing efficiency of up to 140% which is a ratio of healed property value to initial property value or healing efficiency up to 119% if using the healed strength with the damaged strength.     

聚合物基自修复复合材料的研究进展

主要介绍了微胶囊、液芯纤维等不同类型的聚合物基自修复复合材料的制备方法及自修复的基本原理,总结了微胶囊、液芯纤维在聚合物基自修复复合材料中的应用及研究进展,探讨了目前聚合物基自修复复合材料研究中存在的一些难点,最后就自修复材料的发展趋势提出了几点建议.     

X-ray computed tomography proof of bacterial-based self-healing in concrete

Self-healing strategies are regarded as a promising solution to reduce the high maintenance and repair cost of concrete infrastructures. In the present work, a bacterial-based self-healing by use of hydrogel encapsulated bacterial spores (bio-hydrogels) was investigated. The crack closure behavior of the specimens with/without bio-hydrogels was studied quantitatively by light microscopy. To have a view of the self-healing inside the specimens, a high resolution X-ray computed microtomography (X-ray μCT) was used. The total amount and the distribution of the healing products in the whole matrix were investigated. This study indicates that the specimens incorporated with bio-hydrogels had distinct improved healing efficiency compared to the reference ones with pure hydrogel only. The healing ratios in the specimens with bio-hydrogels were in the range from 70% to 100% for the cracks smaller than 0.3 mm, which is more than 50% higher than for the ones with pure hydrogel; and the maximum crack bridging was about 0.5 mm (in 7 d), while pure hydrogels only allowed healing of cracks of about 0.18 mm. The total volume ratio of the healing product in the specimens with bio-hydrogels amounted to 2.2%, which was about 60% higher than for the ones with pure hydrogel (1.37%).     

Effect of Graphite as Forming Additive on Wear Properties of (SiCp + Al2O3f)/Al Composites Prepared by Pressure Infiltration

The 2024Al matrix composites reinforced by 30 vol% SiCp and 10 vol% Al₂O_3f as wear-resistant materials are prepared by pressure infiltration. The graphite powders are added during the preparation of the preform to support shaping. In this article, the effect of the size of the graphite powder on the friction and wear properties of the composites is researched. The results showed that at a given conditions, namely, the size of the SiCp is 14 µm and the diameter of the Al₂O₃ fiber is 4–5 µm, the composites made from 5 ～ 30 µm have a more stable friction coefficience and lower wear rate than those from 30 ～ 50 µm and 50 ～ 70 µm graphite because the diameter of the generated pores in the corresponding preforms is smaller and more concentrated, resulting in a uniform distribution of the reinforcements in the matrix. The detailed effect mechanisms of different graphite sizes on wear and friction properties of the composites as well as the porosity of the corresponding preforms are also discussed.     

Particle-induced damage and subsequent healing of materials: Erosion,corrosion and self-healing coatings

This review summarizes research on particle-induced damage and the subsequent repair of metallic materials. Metallic materials are damaged by solid particle impact via two damage processes: repeated plastic deformation and cutting. At a certain low-impact velocity, the particle does not skid, resulting in only plastic deformation with no damage by cutting. The critical impact velocity has been theoretically derived. Self-healing coatings for repair of damaged materials have been investigated. A fluorine polymer coating has self-healing properties, which are improved by the addition of metal particles. A self-healing coating that uses particles and an organic healing agent has also been developed.     

Linear/network poly(ε-caprolactone) blends exhibiting shape memory assisted self-healing (SMASH)

Self-healing (SH) polymers are responsive polymeric materials that can repair mechanical damage such as cracks in an autonomous fashion. In most SH polymers studies reported to date, crack closure was either unaddressed or achieved by manual intervention. Here, we report a new strategy that utilizes shape memory (SM) to prepare novel SH polymers that are capable of simultaneously closing and rebonding cracks with a simple thermal trigger. This strategy, termed "shape memory assisted self-healing (SMASH)", is demonstrated in a blend system consisting of cross-linked poly(ε-caprolactone) network (n-PCL) with linear poly(ε-caprolactone) (l-PCL) interpenetrating the network, and exhibits a combination of SM response from the network component and SH capacity from the linear component. Thermomechanical analysis revealed that the thermoset, n-PCL, demonstrates reversible plasticity -a form of shape memory where large plastic deformation at room temperature is fully recoverable upon heating. This SM action assists to close any cracks formed during deformation and/or damage while l-PCL chains tackify the crack surfaces by diffusion to the free surface and ultimately across the area of damage during the same heating step as used for SM. In our study, we investigated the controlled damage and SMASH healing of blends with varying composition using tensile testing of essential work of fracture film specimens. The healing component, l-PCL used had a high M(w) (M(w) ～65k g/mol) to enable re-entanglement after diffusion across the interface while the shape memory component, n-PCL was prepared from PCL telechelic diacrylates and a tetrathiol cross-linker, yielding excellent shape memory. We found excellent self-healing of films by the SMASH mechanism, with near complete healing for l-PCL contents exceeding 25 wt %. Applications are envisioned in the area of self-healing bladders, inflated structure membranes, and architectural building envelopes.     

Self-activated healing of delamination damage in woven composites

A study of the healing of delamination damage in woven E-glass/epoxy composites is performed. With the ultimate goal of self-healing in mind, two types of healing processes are studied. In the first a catalyzed monomer is manually injected into the delamination. In the second a self-activated material is created by embedding the catalyst directly into the matrix of the composite, then manually injecting the monomer. Healing efficiencies relative to the virgin fracture toughness of up to 67% are obtained when the catalyzed monomer is injected and about 19% for the self-activated materials. Scanning electron microscopy is used to analyze the fracture surfaces and provide physical evidence of repair.