Reducing the Reprocessing and Healing Temperature of Polyurea with Piperazine-Based Hindered Urea Bonds

Stiff polymers exhibiting good reprocessing and self-healing ability under a moderate stimulus are often desirable for many special applications, but also full of challenges, which come from how to achieve...

Smart Self-Healing Capability of Asphalt Material Using Bionic Microvascular Containing Oily Rejuvenator

It has become one of the research directions of intelligent materials for self-healing asphalt pavements to use a bionic microvascular containing oily rejuvenator. The rejuvenator in a microvascular can carry out the healing of asphalt micro-cracks, thus reducing the damage to and prolonging the life of asphalt pavement. The aim of this work was to investigate the smart self-healing capability of an asphalt/microvascular material through its microstructure and mechanical properties. Microstructure observation indicated no interface separation between the microvasculars and bitumen matrix. Micro-CT images showed that microvasculars dispersed in asphalt samples without accumulation or tangles. The phenomenon of microcracks healing without intervention was observed, which proved that the fractured asphalt sample carried out the self-healing process with the help of rejuvenator diffusing out from the broken microvasculars. The self-healing efficiency of asphalt samples was also evaluated through a tensile test considering the factors of microvasculars content, healing time and healing temperature. It was found that the tensile strength of the asphalt samples was greatly enhanced by the addition of microvasculars under a set test condition. Self-healing efficiency was enhanced with more broken microvasculars in the rupture interface of the asphalt sample. During two self-healing cycles, the self-healing efficiency of the asphalt sample with three microvascular per 1 cm2 of a broken interface were able to reach 80% and 86%. This proves that microvasculars containing rejuvenator play a practical role in the self-healing process of asphalt. With an increase in temperature from 0 to 30 °C, the self-healing capability of the asphalt samples increased dramatically. An increase in time increased the self-healing capability of the bitumen samples. At last, a preliminary mathematical model also deduced that the self-healing efficiency was determined by the individual healing steps, including release, penetration and diffusion of the rejuvenator agent.

Early Age Strength Healing Effect of Cementitious Composite Incorporated Self-Healing Microcapsule

Received 27 February 2019; accepted 02 September 2019 This paper aims to explore early age strength healing effect of cementitious composite incorporated self-healing microcapsule and curing activity of self-healing microcapsule. Particle characteristic of the microcapsule and micromorphology of cement paste incorporated the microcapsule were characterized by SEM. Curing activity of the microcapsule was analyzed by macroscopic solidification test, DSC and TGA. The influence factors of early age strength healing ratio in cementitious composite incorporated self-healing microcapsule were studied. The results showed that epoxy resin microcapsule had favorable micromorphology. Epoxy resin microcapsule core material had good curing activity and possessed the ability to play the healing role in cementitious composite. Healing temperature and healing age had less impact on the healing effect of the microcapsule in cementitious composite. The microcapsule could be kept good shape in cement paste and combined with cement paste closely. The microcapsule also could rupture and had better dispersion in cement paste. The main fracture behavior of the microcapsule was based on small hole ruptured when cement paste did not occur macro damage. When pre-loading was 0.75 σmax, the particle size of microcapsules was range from 75 μm to 150 μm, proportion of epoxy curing agent was 20 % and proportion of the microcapsule was 6 %, early age strength healing ratio reached the highest of 24.1 %.

Experimental assessment of self-healing nature in aluminum-based smart composites with NiTi wires and solder alloy as healing agents through Taguchi approach

In this article, the healing assessment of the AA2014 matrix reinforced with NiTi wires and solder alloy as healing agents is investigated through flexural testing. The idea of a smart composite was such that it could retain its structural stability through NiTi wires reinforced, which ultimately heals the macro cracks, whereas the solder alloy binds the micro-cracks by filling through the gap after heat treatment. The objective of this work is to determine the parameters influencing self-healing assessments. Specimens with different shape memory alloy vol% (0.5%, 1.3%), specimen size (1, 2) and shape memory alloy wires diameter (0.47 mm, 0.96 mm) were fabricated for analysis. Furthermore, Taguchi orthogonal columns of L8 (4^1 2^3) array technique was implemented to study the observations from different experimental runs. Healing temperature (i.e. 600°C) was selected such that it could take advantage of the compositional healing of the matrix. The completely damaged specimens through the bend test were thermally treated at different healing durations (30, 60, 90, 120 min) in a furnace to activate healing. The results show that a maximum of 96.95% of crack depth, 100% of crack width, and 73.76% of the recovery in flexural strength was recovered after heat treatment.

Crack Healing and Mechanical Properties Recovery in SA 508–3 Steel

Internal cracks could be healed under the process of hot plastic deformation. In this study, mechanical properties recovery after crack healing in SA 508–3 steel were investigated. Microstructures of the crack healing zones were observed using an optical microscope (OM) and electron back scattered diffraction (EBSD) technology, and the recovery degrees of mechanical properties in the crack healing zones with the healing temperature and a reduction ratio were tested systematically. The results showed that the internal cracks in SA 508–3 steel disappeared and were replaced by newly formed grains, achieved by recrystallization and abnormal grain growth. The tensile properties of crack healing zones could be fully restored, while their impact and low cycle fatigue properties could only be partially achieved. The recovery degrees of mechanical properties in crack healing zones increased with increasing the healing temperature and reduction ratio in the temperature range of 950–1050 °C. When the temperature was above 1150 °C, the impact properties began to deteriorate because of grain coarsening and larger MA (martensite–austenite) constituents. The microstructural evolution of the crack zone in the SA 508–3 steel was sketched.

Facile Fabrication of a Self-Healing Temperature-Sensitive Sensor Based on Ionogels and Its Application in Detection Human Breath

The biocompatible strechable ionogels were prepared by a facile solution-processed method. The ionogels showed outstanding stretchable and self-healing properties. The electrical property could revert to its original state after 4 s. The repaired ionogels could still bear stretching about 150%. Moreover, the ionogels exhibited high sensitivity and wide-detection range to temperature. The temperature-sensitive sensor could detect the human breath frequency and intensity, showing potential application in detecting disease.

Laboratory Testing of Self-Healing Polymer Modified Asphalt Mixtures Containing Recycled Asphalt Materials (RAP/RAS)

The objective of this study was to evaluate the efficiency of an innovative light-induced self-healing polymers in enhancing the durability of asphalt mixtures and improving its self-healing properties. Mixtures were prepared using two different binders, with and without recycled materials, and self-healing polymer. Results showed that the addition of recycled asphalt material to mixtures prepared with an unmodified binder negatively affected the healing recovery at room temperature. Furthermore, Self-healing properties of the mixtures were improved by increasing the healing temperature. The addition of 5% self-healing polymer to the control mixture, followed by UV light exposure resulted in an increase in self-healing properties of the mixtures prepared with PG 67-22 binder. Semi-Circular Bending (SCB) test results showed that the incorporation of self-healing polymer and 48 h of UV light exposure improved the cracking resistance. Loaded-Wheel Test (LWT) results showed that the self-healing polymer caused an increase in the rut depth of the samples prepared with an unmodified binder. However, the final rut depth was less than the acceptable rutting performance. Thermal-Stress Restrained Specimen Test (TSRST) test results showed that self-healing polymer improved the low temperature cracking performance of the mixtures.

Optimal design of a bio-inspired self-healing metal matrix composite reinforced with NiTi shape memory alloy strips

Utilizing smart materials such as shape memory alloys as reinforcement in metal matrix composites is a novel method to bio-mimic self-healing. This study aims to investigate the influence of design factors of a self-healing metal matrix composite by employing the Taguchi method for designing of the experimental procedure. Three design factors, each in three levels, were studied simultaneously according to L-9 standard Taguchi orthogonal array to determine the optimal level of each factor in mechanical properties enhancement with a reduced number of experiments. Composite specimens were fabricated from Sn-13 wt.% Bi alloy as matrix and nickel–titanium shape memory alloy strips as reinforcement with gravity casting process. Matrix alloy was melted and casted in a preheated metallic mold in which SMA strips were installed in various quantities (one, two, or three strips) and different pre-strains (0%, 2%, or 6%). After fabrication of the specimens, a tensile test was conducted until fracture to specify mechanical properties. Then, specimens were placed in a furnace in three different temperatures (170°C, 180°C, and 190°C) to activate the shape memory effect of strips and achieve crack closure and healing. Specimens were tensile tested again after healing to calculate the amount of healed properties and healing efficiency. Results show that using three strips with 6% of pre-strain and applying 190°C healing temperature can maximize the ultimate tensile strength efficiency. Also, the existence of one strip, 0% pre-strain, and 190°C healing temperature creates the best circumstances for healing ductility.