Strain Energy Absorption Research Articles

Influence of pre-strain on tensile response of extra deep drawing (EDD) steel under varying strain rates and crash performance

This study explores the impact of pre-strain on the uniaxial tensile stress-strain behavior of extra deep drawing (EDD) steel at varying strain rates. The EDD steel blanks were subjected to a uniaxial pre-strain of 15 % in either the transverse or rolling direction. Subsequently, uniaxial tensile tests were conducted at different strain rates, both orthogonal and parallel to the initial pre-straining direction. The study also investigates the alterations in yield stress (YS), ultimate tensile strength (UTS), uniform elongation (UEL), total elongation (TEL), and strain energy absorption (SED, represented by the area under the tensile stress-strain curve) at diverse strain rates after pre-straining. The experimental findings indicate that pre-straining is advantageous for enhancing YS, UTS, and SED. However, this improvement comes at the expense of UEL or TEL. A square crush tube, which shares similarities with automotive components, was examined to assess the crash performance of several automotive structural parts during crash events. A validated constitutive model was used to predict the square tube's energy absorption and crush performance under high-velocity conditions for different pre-straining scenarios.

Flexural and fracture behavior of additively manufactured carbon fiber reinforced polymer composites with bioinspired Bouligand meso-structures

Carbon fiber reinforced polymer (CFRP) composites are strong and lightweight materials extensively used across aerospace, automotive, and construction industries. Bioinspired designs such as Bouligand structures have the potential to improve the mechanical properties of CFRP composites. In this study, we examine the effects of the single and double Bouligand meso-structures with varying twist angles on the flexural and fracture properties of additively manufactured continuous CFRP composites. 3-point flexural tests are conducted to characterize the flexural properties such as flexural modulus, strength, and energy absorption. Single edge notch bend (SENB) tests are performed to quantitively characterize the mode I fracture toughness and effective fracture energy. The elasto-plastic fracture theory is used to quantify the contributions of elastic and plastic energies to the effective fracture energy. Experimental results indicate that twist angles significantly affect the flexural behavior of CFRP composites. The Bouligand meso-structures with a twist angle of 10° increase the flexural strain energy absorption by 2-3 times. The single and double Bouligand layup configurations with the same twist angle result in different flexural properties. In addition, the twist angle affects the magnitude of fracture toughness. A twist angle of 10° results in an improvement of up to 60% in fracture energy dissipation compared to the quasi-isotropic meso-structure. The single and double Bouligand meso-structures with the same twist angle exhibit almost the same fracture toughness and absorbed fracture energy. The Bouligand meso-structures do not increase fracture toughness and elastic fracture energy for crack initiation compared to the quasi-isotropic meso-structure.

Effect of MWCNT on CFRP impregnated with shear thickening fluids under high strain rate impact

This study investigates the effect of multi-walled carbon nanotubes (MWCNT) on the high strain rate properties of carbon fiber reinforced polymer (CFRP) fabric impregnated with shear thickening fluids (STF). Three GFRP-STF and twelve GFRP-MWCNT/STF composite specimens were conducted using a split Hopkinson pressure bar (SHPB). Spherical silica nanoparticles (20.0 wt%) and polyethylene glycol were used to prepare silicon-based-STF (SiO2/STF). On this basis, MWCNT with 0.4, 0.8, and 1.2 wt% were further used to synthesize the MWCNT/STF, respectively. The SHPB test showed that MWCNT/STF has a more significant strain rate effect, with stress increases of 71.1%, 57.5%, and 26.0% under 3800 s−1, 5100 s−1, and 6100 s−1, respectively. The results also showed that MWCNT significantly improved the yield stress and strain energy absorption of SiO2/STF under a high strain rate. The maximum yield stress increase was 71.1%, and the maximum increase in strain energy absorption was 229.1%. The results of CFRP-MWCNT/STF revealed that MWCNT/STF treatment enhanced the high strain rate impact properties of CFRP-SiO2/STF. The improved effect is up to 27.9%, 133.6%, and 165.7% in yield stress, impact toughness, and energy absorption efficiency, respectively. The mass fraction of MWCNT significantly affects the impact properties of CFRP-MWCNT/STF under high strain rate loading, but this effect decreases with the increase of strain rate. Thus, CFRP-MWCNT/STF is more suitable for application in a high strain rate impact environment than CFRP-SiO2/STF.

Dynamic Crushing Behavior of Ethylene Vinyl Acetate Copolymer Foam Based on Energy Method.

This paper aimed to experimentally clarify the dynamic crushing mechanism and performance of ethylene vinyl acetate copolymer (EVA) and analyze the influence of density and thickness on its mechanical behavior and energy absorption properties under dynamic impact loadings. Hence, a series of dynamic compression tests were carried out on EVA foams with different densities and thicknesses. When the impact energy is 66.64 J, for foam with a density of 150 kg/m3, the maximum contact force, maximum displacement, maximum strain, absorbed energy, and specific energy absorption (SEA) increased by 20 ± 2%, -38.5 ± 2%, -38.5 ± 2%, 4 ± 2%, and 105 ± 2%, respectively, compared to foam with a density of 70 kg/m3. The ratios of absorbed energy to impact energy for different thickness specimens are almost equal. The specimen density has no effect on the efficiency of energy absorption and has a greater effect on the SEA. Meanwhile, when the impact energy-to-thickness ratio is 1680 J/m, compared to foam with a thickness of 30 mm, the maximum contact force, maximum displacement, maximum strain, absorbed energy, and SEA for foam with a thickness of 60 mm increased by 28.5 ± 2%, 211.3 ± 2%, 56.6 ± 2%, 100.8 ± 2%, and 0.4 ± 0.5%, respectively. When the impact energy is 66.64 J, compared to foam with a thickness of 30 mm, the maximum contact force, maximum displacement, maximum stain, absorbed energy, and SEA for foam with a thickness of 60 mm increased by -42.5 ± 2%, 163.5 ± 2%, 31.7 ± 2%, 4.1 ± 2%, and 4.1 ± 2%, respectively. The SEA of two different-thickness EVA specimens is almost equal, about 2.8 J/g. The ratios of absorbed energy to impact energy for different thickness specimens are almost equal, both at 72%. The specimen thickness has no effect on the efficiency of energy absorption and has a greater effect on the maximum contact force. In the range of impact energy, thickness, and density studied, the absorbed energy and SEA are not affected by the thickness of EVA specimens and are determined by the impact energy. The density has no significant effect on the absorbed energy but has a greater effect on the SEA. However, for EVA foams, the greater the density, the greater the mass, and the higher the cost. Taking into account lightweight and cost factors, when optimizing cushioning design within a safe range, we can choose EVA foams with a smaller density and thickness.

Effect of moisture content on mechanical behavior of ultra-high toughness cementitious composites

This study presented an investigation into the basic mechanical properties of Ultra-high toughness cementitious composites (UHTCC) under varying moisture levels (0%, 56.5%, and 100%). UHTCC have been recognized for their excellent deformation and crack control abilities, making them ideal for repairing and reinforcing hydraulic structures. In this study, static compressive test and direct tensile test were conducted to determine the influence of free water on compressive strength, tensile stress and strain relationship, elastic modulus and energy absorption ability of UHTCC. Meanwhile, the notched beam fracture test and single fiber pull-out test were also performed to investigate the mechanism behind such phenomenon. The results of the study revealed that as the relative moisture content of UHTCC increased, the compressive and tensile strengths decreased to varying degrees. The softening effect of water on compressive strength of UHTCC was found to be more significant than that on its tensile strength. Furthermore, the direct tensile deformation capacity of UHTCC increased from 2.4% to 4.0% as the relative moisture content increased. Water infiltration into UHTCC was found to have a minimal effect on the number of tensile cracks but significantly increased their width. The results of notched beam fracture and fiber pull-out tests demonstrated that water infiltration led to a 30.4% decrease in matrix fracture toughness, a 37.3% decrease in chemical bonding strength, and a 23.4% decrease in frictional bonding strength between fibers and the matrix. The increased deformation ability of UHTCC in water environments was attributed to the increase in strain hardening energy index (Jb’/Jtip).

Effects of ZnO nanowire and silica coatings on the inter-yarn friction and ballistic properties of Kevlar fabrics

This paper focused on improving the ballistic performance of plain weave (PW) and twill weave (TW) Kevlar fabrics without affecting the weight. Single layers of fabrics were subjected to two different surface coatings, one with ZnO nanowires (ZnO NW) and other with Silica nanoparticles. Tensile, inter-yarn friction and ballistic properties of bare and surface coated fabrics were evaluated and compared with each other. All types of PW fabrics were found to have superior tensile strain energy, inter-yarn friction and ballistic energy absorption than corresponding TW fabrics. Both ZnO NW and Silica coatings were found to significantly improve the strain energy, inter-yarn friction and ballistic energy absorption of fabrics with only less than 8% increase in the areal density of the fabrics. Among the two surface treatments, Silica coating was found to provide maximum improvement in properties. It increased the strain energy, yarn pull-out energy and ballistic energy absorption in PW fabrics by 67%, 694% and at least 240%, respectively. Also, it increased the strain energy, yarn pull-out energy and ballistic energy absorption in TW fabrics by 42%, 1350% and 387%, respectively. The work demonstrated promising ways of improving the ballistic performance of Kevlar fabrics.

Early-age mechanical properties and constitutive model of polystyrene concrete under impact load

The dynamic mechanical tests of polystyrene concrete with ages of 12 h, 24 h and 36 h and 28 d were carried out by Φ 100 mm SHPB equipment. The effects of strain rate and age on dynamic mechanical properties of polystyrene concrete were analyzed in terms of the relationship between strain rate and impact velocity, strength characteristics, deformation characteristics and energy absorption characteristics. And based on Saenz model, the early-age dynamic constitutive model of polystyrene concrete was constructed. The results show that the strain rate of polystyrene concrete is positively correlated with the impact velocity. At the same impact velocity, the strain rate of polystyrene concrete decreases with age. The strength characteristic indicators, deformation characteristic indicators and energy absorption characteristic indicator of polystyrene concrete all have strain rate strengthening effect, and all these indicators and the strain rate sensitivity of these indicators increase with age. Polystyrene concrete has good deformation and energy absorption characteristics at early age. At the age of 36 h, the peak strain, ultimate strain and specific energy absorption of polystyrene concrete can reach 77∼80%, 95∼106% and 86∼92% of that at the age of 28 d, respectively. The constructed dynamic constitutive model is reasonable and reliable, and it can be used to describe the mechanical behavior of polystyrene concrete at early age under impact load.

Compaction behaviour of weft-knitted rib fabrics from glass yarn

Single- and multi-layer compressibility behaviors of weft-knitted glass yarn fabrics with 1x1, 2x2, English and fisherman rib architectures were analyzed in this study. Compaction and relaxation curves were modeled with the power-law ( P = a V f n where P , and V f are pressure and fiber volume fraction, respectively). The analysis of “ a ” constant (i.e. pressure to achieve fiber volume fraction of one) revealed that: 1) repetitive relaxation and reloading to maximum compaction stiffened the fabric stack and improved the fiber content 2) 1x1 rib architecture required the highest compaction to achieve fiber volume fraction of one due to its loose and porous structure 3) adjacent fabric layers nested in each other in multi-layer fabrics. The analysis of “ n ” exponent (stiffening index) indicated that: 1) initial compaction stiffened the fabric stack 2) while the slack English rib architecture exhibited the lowest index, the tight fisherman rib exhibited the highest index 3) number of layer did not alter the index. Absorbed strain energy analysis indicated that 1x1 and 2x2 ribs relaxed better than the other architectures. The side-by-side and alternating placement of face and back plain loop bars in these architectures eased the sliding of the bars over each other that increased the energy absorption. The number of fabric layer increased the relaxation at statistically insignificant level.

Effects of different joint wall lengths on in-plane compression properties of 3D braided jute/epoxy composite honeycombs

To comply with the trend in the development of engineering materials towards lightweight, high strength, eco-friendly, sustainable, and multi-functional, a three-dimensional braided integrated composite honeycomb is designed. The effects of geometrical parameters particularly joint wall lengths on the in-plane mechanical behavior of the honeycombs were investigated. The results show that the in-plane mechanical properties are related to the number of cell walls, and the angle between the cell wall and the loading direction. Increasing the number of cell rows to double and triple at similar areal density lead to an improvement of the maximum load up to 2.5, and 3.8 times, respectively. Similarly, the total absorbed strain energy increased up to 2.6 and 5.9 times, respectively. The displacement at the maximum load is increased by 1.6 and 2.7 times as a result of increasing the cell row number. The total absorbed strain energy increased to 1.7 and 1.3 times, respectively. The failure angle of the 3D braided composite honeycomb is about 4°–7°. This investigation presents the geometrical factors of a 3D braided composite honeycomb can be further designed and optimized, but it also provides a reference for the development and design of a new composite honeycomb.

Influence of curing conditions on mechanical and microstructural properties of ultra-high-performance strain-hardening cementitious composites with strain capacity up to 17.3%

This study investigated the mechanical properties and microstructural characteristics of ultra-high-performance strain-hardening cementitious composites (UHP-SHCC). The mechanical properties were thoroughly analyzed based on the shrinkage behavior, thermogravimetric analysis, mercury intrusion porosimetry, and scanning electron microscopic images. Three relative humidity (RH) conditions and curing ages were set as the test variables. Relative to the specimens cured at 30% RH, the specimens cured at 60% and 100% RH conditions showed 29.9% and 37.6% higher 91-day compressive strengths. Excellent strain-hardening behaviors with very high strain capacities, ranging between 6.0% and 17.3%, were obtained for all UHP-SHCC specimens tested. The highest strain capacity and energy absorption capacity of 17.3% and 1310.7 kJ/m3 were obtained when cured under RH conditions of 30% and 60% for 7 days, respectively. The strain capacity and energy absorption capacity of UHP-SHCC rather decreased as the RH condition and curing age increased to 100% and 91 days, respectively.

Experimental and numerical studies on flexural behaviour of lightweight and sustainable precast fibre reinforced hollow core slabs

This study reports experimental and numerical studies on the flexural behaviour of sustainable fibre reinforced lightweight hollow core slabs (FR-LWHCS). An innovative and sustainable LWHCS is proposed for structural applications using a lightweight concrete mix of 1800 kg/m3 density, previously developed by authors. Full-scale precast LWHCS specimens are cast and tested under flexure using a four-point loading configuration. A high shear span to depth (a/d) ratio of 10 is chosen to have flexure dominant behavior. FR-LWHCS is made using sintered fly ash aggregate (SFA) as coarse aggregate and monofilament macro synthetic fibres of different volumetric fibre dosages (0.4 % and 0.6 %). A small dosage of micro synthetic fibres of 0.02 % by volume is also added to arrest shrinkage cracks. Two control slabs, one constructed with lightweight concrete and the other with conventional normal density concrete, are tested. The digital image correlation (DIC) technique is used to track the cracks and failure modes. A 3D finite element analysis is performed to supplement the test results. Test results show that FR-LWHCS satisfies all the structural requirements, leading to economy and sustainability. FR-LWHCS with 0.6 % fibre dosage performed better than hollow core slabs made of normal density concrete. Though the addition of fibres did not considerably increase peak load, a minimum dosage of fibre addition is warranted in LWHCS to improve the serviceability performance. Fibre addition significantly improved the strain energy absorption.

Nano filler incorporated epoxy based natural hybrid fiber confinement of concrete systems: Effect of fiber layers and nano filler addition

The utilization of environment friendly materials in the construction industry is essential for sustainable development. For the purpose of strengthening and retrofitting concrete structures, fiber reinforced polymer (FRP) composites have been predominantly used. In the area of structural strengthening, as an alternative to synthetic fiber reinforced composites, the application of natural fiber reinforced composites is of immense interest. This study discusses the mechanical properties of externally strengthened concrete cylinders using a natural hybrid fiber system with two layers of sisal fiber sheets followed by 1 to 3 layers of basalt fiber sheets. In addition, the effect of multi walled carbon nanotubes (MWCNT) incorporation in the epoxy matrix from 0.5 to 1.5 wt%, on the various properties are analyzed. The inclusion of MWCNT in the epoxy matrix improved the overall performance of the FRP significantly. The results show that there is substantial improvement in mechanical properties up to 1 wt% MWCNT content in composites, beyond which it is reduced due to agglomeration of nanofiller. The MWCNT incorporated epoxy based five layered hybrid sisal basalt FRP confined specimens showed an improvement of 114% and 427% in peak strength and strain values under axial compressive strength tests. Moreover, the axial compressive behavior, stress–strain response, energy absorption and ductility characteristics of the confined column specimens were evaluated. The major focus of the study is to assess the influence of basalt FRP layers on the ultimate load carrying capacity and performance of hybrid sisal basalt FRP (HSBFRP) confined specimens. Statistical analysis of variance (ANOVA) was carried out and revealed that the number of FRP layers and addition of MWCNT in epoxy significantly affect the overall performance. The addition of basalt fiber layers in hybrid sisal basalt FRP systems is found to improve the load carrying capacity and energy absorption characteristics of confined specimens. Therefore, HSBFRP confinement can be used in areas where moderate strength and greater ductility is commanded.

In-plane dynamics of circular cell hexagonally packaged honeycombs in two principal axes

The in-plane deformation modes, stress–strain curves and energy absorption characteristics of circular cell hexagonally packaged honeycombs with the linear elastic and plastic base material with linear strain hardening are numerically investigated under crushing velocities in two principal axes. Three deformation modes are observed and the empirical formulas for critical velocities of deformation mode transition are derived. With increasing crushing velocities, the fluctuation of stress becomes more intense in the plateau stress phase of stress–strain curves, which appears from low-crushing velocities in x2 direction, while in x1 direction at high velocities. Densification strain is linear with t/R ratio for a given crushing velocity, and becomes larger with increasing velocities approximately in a linear relationship under a deformation mode for a given t/R ratio. The law of mean plateau stress is consistent with a one-dimensional shock wave model and static plateau stress is proportional to the square of relative density. Three types of empirical expressions of mean plateau stress are derived. Crushing force efficiency is approximately independent of t/R ratio and sensitive to crushing velocity. Crushing force efficiency becomes smaller and then reduces with increasing velocities, and fluctuates around a level under dynamic mode.

Experimental and numerical study on behaviour of fibre reinforced lightweight hollow core slabs under different flexure to shear ratios

The current work explores the behaviour of fibre-reinforced lightweight hollow core slabs (FR-LWHCS) intending to develop sustainable construction solutions. The FR-LWHCS investigated in this work contains sintered fly ash aggregate (SFA) as coarse aggregate. Due to the use of SFA, the behaviour of LWHCS is expected to be different from the hollow core slabs (HCS) constructed using normal density concrete. FR-LWHCS are tested at different shear span to depth (a/d) ratios of 3.5, 7 and 10 to understand the shear and flexure behaviour. Twelve full-scale hollow core slab (HCS) specimens of 3400 mm length, 600 mm width, and 150 mm thickness are tested. FR-LWHCS consists of monofilament macro synthetic fibre dosages of 0.4 %, and 0.6 %, along with fibrillated micro fibre of 0.02 % dosage. The digital image correlation (DIC) technique is adopted to understand the strain profile on the HCS at different levels of loading. The numerical analysis is performed using a commercially available finite element software and is corroborated with experimental findings and parametric studies have been performed. Both LWHCS and normal HCS specimens failed in shear, flexural-shear and flexure modes at a/d ratios of 3.5, 7 and 10, respectively. The addition of fibres increased the peak load by 65 % compared to control LWHCS specimens tested at an a/d ratio of 3.5. The use of fibres increased strain energy absorption and changed the failure to less brittle mode at all a/d ratios. The fibre reinforced specimens have nearly 3.5 times, 2.5 times and 1.3 times the strain energy absorption of the control LWHCS when tested at a/d ratio 3.5, 7 and 10 respectively.

Dynamic compressive properties of new metallic hollow sphere concrete composites

The dynamic properties of new metallic hollow sphere concrete composites were investigated experimentally. Metallic hollow spheres (MHSs) at volume fractions of 10 %, 20 % and 30 % were embedded into a concrete matrix to form metallic hollow sphere concrete composites (MHSCCs) under normal temperature conditions. Dynamic compression tests using a split Hopkinson pressure bar were conducted at strain rates in the 15 s−1 ∼ 80 s−1 range on the specimens after 28 d of curing. The conditions of the concrete matrix, with and without polypropylene fibres, were tested for comparison. The failure modes, stress–strain curves, dynamic strengths, and energy absorption capacities were analysed. The results indicated that the damage degree increased with increasing MHS content and strain rate. The composites were more sensitive than plain concrete to the strain rate. Adding a certain amount of MHSs into the concrete matrix improved the dynamic compressive strength and the overall energy absorption by up to 25.4 % and 317 %, respectively, at a strain rate of approximately 70 s−1. The addition of polypropylene fibre further improved the dynamic properties of the composites due to the bridging effect of fibres; however, it had a negative influence on the dynamic increase factor.

Mechanical Properties and Energy Characteristics of Flawed Samples with Two Non-Parallel Flaws under Uniaxial Compression

Unequal flaws are widespread in rock engineering, in which the extensions induced by excavation and unloading are the main factors leading to engineering instability. Rock deformation and failure are essentially the results of energy transmission. In order to study the influence of flaw type and angle on the mechanical properties and energy characteristics of the flawed rock mass, uniaxial compression tests were conducted using particle flow numerical analysis software. The results show that the crack initiation strength and peak strength of the sample increase with the increase in the flaw angle. For smaller flaw angles, the sample shows obvious plastic deformation during uniaxial compression. For larger flaw angles, the sample shows elastic–brittle properties, whose storage energy is larger. The peak strength of samples with flaws of unequal length presents an obvious decrease compared with that of flawed samples with flaws of equal length, and the extent of the reduction is 6.15% on average. Unequal flaws decrease the ability of the flawed sample to absorb strain energy. Compared with flawed samples with equal flaws, flawed samples with unequal flaws decrease the boundary energy and elastic strain energy by 9.29% and 9.95% on average, respectively. Flaws of unequal length in this sample can weaken the performance of the flawed sample.

Experimental investigation of the in-plane quasi-static mechanical behaviour of additively-manufactured polyethylene terephthalate/organically modified montmorillonite nanoclay composite auxetic structures

Apart from the inherent anomalous behaviour under tensile and compressive structures, auxetic structures have shown improved energy absorption characteristics that are of prime interest to various fields of study. This is further exemplified by additive manufacturing (AM) techniques and polymer composites to tailor the shape, geometry and form of these structures. Consequently, this paper aims to characterise the in-plane compressive behaviour and negative Poisson’s ratio (NPR) of the most prominent auxetic structures fabricated additively used polymer nanocomposite materials. The study incorporates the use of glycol-modified polyethylene terephthalate (PETG) and nanocomposites of PETG filled with organically modified montmorillonite (OMMT) nanoclay particles to produce auxetic structures fabricated through fused filament fabrication (FFF). Different structures such as hexagonal re-entrant honeycomb structures, peanut-shaped honeycombs, chiral honeycomb structures and missing rib structures are characterised for their compressive performance through experimental approaches involving mechanical testing and digital image correlation (DIC). Different parameters such as the peak crushing strength, average crushing strength, NPR, specific energy absorption (SEA), and crush force efficiency (CFE) of these structures are evaluated at different strain rates/loading rates for varying concentrations of nanoclay and PETG. It is observed that higher loadings of nanoclay particles lower the compressive strength of the structures. Additionally, the NPR decreases with increasing strain rates and is also influenced by the composition and the resultant stiffness. Moreover, the geometrical parameters of the structure largely influence its strain energy absorption. The results have shown that such material-structure combinations can produce structures of high-performance capabilities suitable for aerospace applications.

Compressive Behavior of Interlocking Plastic Blocks Structural Elements Having Slenderness

Earthquakes are among of the most harmful and potentially fatal natural disasters. Masonry structures in seismic zones of urban and rural areas around the world pose a threat to human life. Housing that is both affordable and earthquake-resistant in earthquake-prone areas is currently in demand in developing countries. For affordable earthquake-resistant structures in earthquake-prone areas, numerous researchers have studied mortar-free interlocking structures. Plastic blocks are used in order to reduce the mass of the overall structure. To start with, structures under gravity are explored first because more than 95% of its design life, any structure has to withstand gravity. Prototypes of interlocking plastic-block columns, solid walls, and walls with an opening are considered for making the mortar-free structures. In this study, the effect of slenderness on the behavior of interlocking-plastic-block structural elements is investigated under compressive loading by a servo-hydraulic testing machine in the laboratory. The effect of slenderness on the behavior of one and two-block-wide structural elements was investigated in terms of the stress–strain curve, energy absorption, and toughness index under compressive loadings. Correlations between the compressive strength of interlocking-plastic-block structural elements with varying thicknesses were found. Scaled-down prototypes of interlocking-plastic-block structural elements having two-block wide depicted more resistance to compressive loads than one block wide structural elements. The correlations among the one and two block wide interlocking-plastic-block columns, single and double-block-wide solid walls, and single and double-block-width walls with an opening found in this analysis were Pdc = 2.2 Psc, Pdsw = 2.9 Pssw, and Pdwo = 3.5 Pswo. This study can be applied in the future to better understand the detailed behavior of interlocking plastic blocks.

Controlling the hierarchical microstructure of bioceramic scaffolds by 3D printing of emulsion inks

Mechanical and biological properties constitute the most fundamental requirements for bone tissue engineering (BTE) scaffolds. Nonetheless, existing fabrication strategies find it difficult to prepare highly porous BTE scaffolds for improved biological properties while also preserving sufficient mechanical properties that are compatible with the natural bone. Inspired by the hierarchical porous materials in Nature, hierarchical porous BTE scaffolds can achieve a combination of superior mechanical efficiency and biological functions. With this in mind, this study reports the fabrication of hierarchical porous hydroxyapatite (hpHA) scaffolds by 3D printing of emulsion inks. The scaffolds exhibit high porosity up to 73.7%, featuring 3D printed macropores of 300 – 400 µm and emulsion templated microporosity of < 20 µm. Via formulation of the emulsion inks, such as varying the oil volume and adding Pluronic® F-127, this process demonstrates effective control of the microporosity and pore morphology of the scaffolds. The scaffolds are mechanically compatible with the natural cancellous bone, with compressive strength in the range of 1.41 – 7.84 MPa and Young’s modulus of 57.3 – 304 MPa. Furthermore, the elastic admissible strain (EAS) and specific energy absorption (SEA) of the hpHA scaffolds can be increased up to 4.4% and 1.22 kJ/kg, respectively, indicating greatly enhanced mechanical performances owing to the hierarchical porous structure. Meanwhile, improved cell attachment, spreading and proliferation are observed in these scaffolds with their additional microporosity. Hence, the hpHA scaffolds in this study show great potential in BTE applications, and the reported process of 3D printing of emulsion inks is a promising fabrication strategy for further optimization of highly porous BTE scaffolds.

Effect of long aramid fiber on the properties of styrene‐butadiene rubber composites based on extrusion

AbstractIn this paper, long aramid fiber (LAF) reinforced styrene‐butadiene rubber/carbon black composites was prepared via a high pressure and low shear rate extrusion process, and the average length of the remaining fiber exceeded 6 mm. With LAF as reinforcement phase, the bonding between the fiber coated with butadiene styrene vinyl‐pyridine rubber latex and rubber matrix was increased. The results showed that the addition of LAF improved the properties of the composites, particularly in terms of dynamic fatigue life of the notched samples, which was increased by 352.7%. The long fibers with good interfacial bonding were peeled off in fatigue process, which can significantly absorb strain energy; thus, the propagation of fatigue cracks was effectively inhibited. This study proposes a feasible strategy to significantly improve the service life of rubber products under alternating stress, such as tires, by using the reinforcement of long fiber.