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Some traditional building materials, such as concrete and steel, have a negative impact on the environment. With the in-depth implementation of sustainable development, green materials are gradually being considered, and bamboo is a green high-energy building material. However, there have been few studies on the prediction of mechanical properties of bamboo. In order to predict the longitudinal compressive properties of bamboo, tests were carried out on the longitudinal compressive tests of bamboo. The failure mode was explored, as well as the relationship between the physical and mechanical properties of bamboo. Prediction formulas were developed for the longitudinal compressive properties of bamboo. The results showed that the failure mode of the longitudinal compressive test of bamboo was ductile failure. The wall thickness and diameter of bamboo were found to be positively correlated with height. The longitudinal compressive strength and elastic modulus were positively correlated with height and negatively correlated with wall thickness and diameter. The longitudinal compressive strength and elastic modulus were positively correlated with height. The linear model can be used to fit the relationship between mechanical properties and height. This research provides a reference for the prediction of bamboo properties.

Slurry-infiltrated fiber concrete (SIFCON) is a sort of strain hardening cement-based composite material, typically made with 5%–20% steel fibers. This study focused on a novel type of SIFCON in which hooked-end steel fibers were replaced by arc-shaped steel fibers. The quasi-static compressive properties of the SIFCON were first measured. Test results suggested that using arc-shaped steel fibers in lieu of hooked-end steel fibers increased the quasi-static compressive strength by 47.1% and the strain at peak stress by 56.3%. We attribute these improvements to new crack-resisting mechanisms, namely “fiber cross-lock”, “dual bridging”, and “confinement loops”, when the arc-shaped steel fibers are introduced into SIFCON. As high impact resistance is a special property of SIFCON that is of practical significance, the dynamic compressive properties of arc-shaped steel fiber SIFCON were studied by using an 80-mm-diameter split Hopkinson pressure bar (SHPB). The results showed that the dynamic compressive strength, dynamic increase factor (DIF), and dynamic toughness of SIFCON all increased with the strain rate. The SIFCON incorporating arc-shaped steel fibers proved to have significant advantages in structural applications requiring high impact resistance.

For the development of lightweight biomimetic materials, the compressive properties of the beetle elytron plate (BEP, a type of biomimetic sandwich plate inspired from beetle elytra) and the underlying mechanism thereof were investigated. With the following results: (1) The shared mechanism of trabeculae was revealed by using structural analysis. It is further predicted that a BEP with hollow trabeculae should possess enhanced compressive properties. (2) When the trabecular number (N) in a hexagonal unit of the honeycomb is less than three, the compressive strength of the BEP is rapidly increased with the increment of N. When N is over four, the deformation capacity is significantly improved because of the arising of S-type buckling deformation in the core structure of the BEP. Furthermore, the definition of the BEP is proposed combined with the biological structure of the beetle elytra. (3) When N=6 and the external diameter of trabeculae is equal to the length of honeycomb walls, the synergistic mechanism between the trabeculae and the honeycomb walls in BEPs is fully exerted. Namely, the trabecula restricts the deformation of the honeycomb walls; in turn, the honeycomb walls provide lateral support for the trabecula. This mechanism leads the core in the BEP to generate an S-type global buckling deformation producing the best compressive properties. The results will greatly impact the biomimetic field of beetle elytra and many industries in which honeycomb structure also serves as a key component.

This study investigates the properties of 3D-printed composite structures made from polylactic acid (PLA) and lightweight-polylactic acid (LW-PLA) filaments using dual-nozzle fused-deposition modeling (FDM) 3D printing. Composite structures were modeled by creating three types of cubes: (i) ST4—built with a total of four alternating layers of the two filaments in the z-axis, (ii) ST8—eight alternating layers of the two filaments, and (iii) CH4—a checkered pattern with four alternating divisions along the x, y, and z axes. Each composite structure was analyzed for printing time and weight, morphology, and compressive properties under varying nozzle temperatures and infill densities. Results indicated that higher nozzle temperatures (230 °C and 240 °C) activate foaming, particularly in ST4 and ST8 at 100% infill density. These structures were 103.5% larger on one side than the modeled dimensions and up to 9.25% lighter. The 100% infill density of ST4-Com-PLA/LW-PLA-240 improved toughness by 246.5% due to better pore compression. The ST4 and ST8 cubes exhibited decreased stiffness with increasing temperatures, while CH4 maintained consistent compressive properties across different conditions. This study confirmed that the characteristics of LW-PLA become more pronounced as the material is printed continuously, with ST4 showing the strongest effect, followed by ST8 and CH4. It highlights the importance of adjusting nozzle temperature and infill density to control foaming, density, and mechanical properties. Overall optimal conditions are 230 °C and 50% infill density, which provide a balance of strength and toughness for applications.

Background Dynamic compressive strength (DCS) of frozen rocks is significant in improving the impact design of rock engineering in cold regions. However, the existing dynamic low temperature testing systems generally cannot achieve a controllable cooling rate or maintain a stable freezing temperature environment, which induces undesirable damage in rocks due to the rapid cooling rate and leads to inaccurate measurement results. Objective The objective of this study is to develop a valid dynamic low temperature testing system capable of testing frozen rocks and investigate the effect of ambient sub-zero temperature on the dynamic compressive behaviors of rocks. Methods The T 2 spectrums obtained by NMR (Nuclear Magnetic Resonance) of two freezing conditions are adopted to prove the necessity of ambient sub-zero temperature for dynamic tests of frozen rocks. A valid dynamic low temperature testing system is developed to perform the dynamic rock test under the ambient sub-zero temperature of dry and saturated white sandstone specimens at 20 °C, -10 °C, and -20 °C. The DCSs (dynamic compressive strength) of dry and saturated porous white sandstones at 20 °C, -10 °C, and -20 °C are obtained and compared. Results The dynamic low temperature testing system is valid for performing the dynamic rock test under ambient sub-zero temperature and capturing the dynamic failure process of frozen rock specimens. At 20 °C, -10 °C, and -20 °C, the DCSs of dry sandstones are higher than those of saturated sandstones, and the sub-zero temperature has a different influence on the DCSs of dry and saturated sandstones, indicating that both the phase transition of water and the shrinkage of minerals contribute to the DCS deterioration. Conclusions Ambient sub-zero temperature of dynamic testing frozen rocks is necessary to evaluate the significant temperature influence on the dynamic compressive behavior of sandstone.

This experimental study explored the impact of varying weight proportions (5%, 10%, 15%, and 20%) of cotton fiber reinforcement in epoxy composites on compressive strength, Charpy impact strength, and water absorption characteristics. Concurrently, the interfacial properties were examined using Scanning Electron Microscopy (SEM). The inclusion of 15 wt.% cotton fiber notably enhanced compressive strength, displaying consistent improvement as cotton content increased until reaching 15 wt.%. Beyond this point, further increases yielded diminishing enhancements in compressive properties. EC20 demonstrated superior impact strength and energy absorption. Increased cotton concentrations improved impact properties due to the fibrous nature of cotton, enhancing energy dissipation and crack resistance within the epoxy matrix. Higher cotton content correlated with increased water absorption, aligning with cotton’s hydrophilic properties. The EC20 composite exhibited heightened water uptake and permeability, indicating the influence of elevated cotton concentrations. SEM analysis of fracture surfaces identified crucial features such as fiber pull-out, matrix cracking, interfacial debonding, and surface irregularities. These findings contribute significantly to understanding the inherent failure mechanisms in these composite materials.

This study purposed to develop conductivity 3D printed (3DP) fingertips and confirm their potential for use in a pressure sensor. Index fingertips were 3D printed using thermoplastic polyurethane filament with three types of infill patterns (Zigzag (ZG), Triangles (TR), Honeycomb (HN)) and densities (20%, 50%, 80%). Hence, the 3DP index fingertip was dip-coated with 8 wt% graphene/waterborne polyurethane composite solution. The coated 3DP index fingertips were analyzed by appearance property, weight changes, compressive property, and electrical property. As results, the weight increased from 1.8 g to 2.9 g as infill density increased. By infill pattern, ZG was the largest, and the pick-up rate decreased from 18.9% for 20% infill density to 4.5% for 80% infill density. Compressive properties were confirmed. Compressive strength increased as infill density increased. In addition, the compressive strength after coating was improved more than 1000 times. Especially, TR had excellent compressive toughness as 13.9 J for 20%, 17.2 J for 50%, and 27.9 J for 80%. In the case of electrical properties, the current become excellent at 20% infill density. By infill patterns at 20% infill density, TR has 0.22 mA as the best conductivity. Therefore, we confirmed the conductivity of 3DP fingertips, and the infill pattern of TR at 20% was most suitable.

Using polypropylene (PP) fiber and cement to modify iron-ore tailing and applying it to road engineering is an effective way to reuse iron-ore tailing. The compressive properties and deformation characteristics of PP-fiber-and-cement-modified iron-ore tailing (FCIT) under traffic load were studied by the unconfined-compressive-strength (UCS) test and the dynamical-triaxial (DT) test. The test results indicated that the UCS and residual strength both increased with increasing PP-fiber content, and tensile and toughness properties were positively correlated with PP-fiber content. Moreover, the dynamic elastic modulus and damping of FCIT both showed a negative linear relationship with cycle time. It can be found from the test results that 0.75% was the best PP-fiber content to modify iron tailing sand in this work. Lastly, a prediction model was developed to describe the relationship between the cumulative plastic strain, PP-fiber content and cycle time, which can effectively capture the evolution law of the cumulative plastic strain with cycle time of FCITs at different PP-fiber contents.

As renewable and environment-friendly materials, coir and sisal natural fibers can be used in soil reinforcement with minimum cost and other benefits. In this study, we focused on their improvements of unconfined compressive properties of polymer treated sand. In total, 36 groups of unconfined compressive strength tests, combined with X-ray diffraction and scanning electron microscope investigations were performed. We had studied the effects of polymer and fiber contents, and fiber types on the reinforcement effectiveness. The results showed that both coir and sisal fiber can improve the mechanical properties and microstructure of treated sand. In terms of strength properties, sisal fiber inclusion was better than coir fiber, while both have a similar reinforcement benefit on soil ductile behaviors. The strength and compressive energy increased with an increment in polymer and fiber content. The reinforced sand can have up to 1 MPa compressive strength and 140 kPa compressive energy for coir fiber inclusion, while 1.2 MPa and 170 kPa, respectively, for sisal fiber. The axial stress-strain characteristics and failure patterns were also improved, and the brittle index decreased toward zero, which suggests an increasing ductile. The polymer membrane enwrapping and bonding sand grains, and the network structure built by fiber crossing and overlapping among sand grains, as well as the interfacial attachment conferred by polymer between sand grains and fiber, all contributed to the reinforcement of treated sand.

Desulfurization slag (DS) is the solid waste discharged from the bottom of the circulating fluidized bed (CFB) boiler. It has good pozzolanic activity, self-hardening property and large expansibility. In this paper, ground desulfurization slag (GDS) is used as mineral admixture to replace cement to prepare self-compacting concrete (SCC). In order to find out the influence laws of different factors on the axial compressive properties of the self-compacting concrete filled steel tube (CFST), seven types of SCC are prepared and nine groups of CFST short column are fabricated. Filling ability test, compressive strength test and axial compressive test are performed. The filling ability and the compressive strength of the SCCs are investigated, and the axial compressive properties of the CFSTs are researched. The results show that the amount of polycarboxylate superplasticizer (PS) increases with the amount of GDS, and the addition of GDS decreases the 3d, 7d and 28d compressive strength of the SCCs. The optimum amount of GDS for SCCs and CFSTs is 30%. When the amount of GDS is 30%, the ultimate bearing capacity of CFST short column (GP3) is the highest, which is 33.6% higher than that of GP1 without GDS. The influence law of the GDS’s amount on the CFSTs’ ultimate bearing capacity is quite different from that of the GDS’s amount on the SCCs’ compressive strength. The ultimate bearing capacity of CFSTs can be significantly improved by adding GDS. Sodium sulfate can improve both the compressive strength of the SCC and the bearing capacity of the CFST.