Quasi-static uni-axial compression behaviour of hollow glass microspheres/epoxy based syntactic foams

Hollow glass microspheres/epoxy foams of different densities were prepared by stir casting process in order to investigate their mechanical properties. The effect of hollow spheres content and wall thickness of the microspheres on the mechanical response of these foams is studied extensively through a series of quasi-static uni-axial compression tests performed at a constant strain rate of 0.001 s^?1. It is found that strength of these foams decreases linearly from 105 MPa (for the pure resin) to 25 MPa (for foam reinforced with 60 vol.% hollow microspheres) with increase in hollow spheres content. However, foams prepared using hollow spheres with a higher density possess higher strength than those prepared with a lower one. The energy absorption capacity increases till a critical volume fraction (40 vol.% of the hollow microspheres content) and then decreases. Failure and fracture of these materials occur through shear yielding of the matrix followed by axial splitting beyond a critical volume fraction.     

A study of fabricating and compressive properties of cellular Al–Si (355.0) foam using TiH2

Al–Si (355.0) alloy foam has been produced by Alporas method (in which foam alloy melts, and titanium hydride is used as a blowing agent). Mechanical behavior such as quasi-static compression (strain–stress curves, energy absorption capacity), also the effects of thermal properties on the macroscopic structure of the produced foam were investigated. In addition, the effect of energy absorption capacity on percentage porosity has also been studied. The research shows that the produced foam with an average cell size and proper distribution has a more mechanical stability compared to the foams with no such characteristics. It was found that yield strength tends to increase from 12.51 MPa for porosity 74.0% to 22.32 MPa for porosity 54.0%. This foam has also been compared with other foams such as Al-pure foam and Mg foam. It can be stated that Al–Si (355.0) foam has a higher yield strength in comparison to Al-pure foam and Mg foam.     

Cytocompatibility and mechanical properties of novel porous 316 L stainless steel

Novel 316 L stainless steel (SS) foam with 85% porosity and an open pore diameter of 70–440 μm was developed for hard tissue application. The foam sheet with a 200-μm diameter had superior cell proliferation and penetration as identified through in vitro experiments. Calcification of human osteosarcoma cells in the SS foam was observed. Multi-layered foam preparation is a potential alternative technique that satisfies multi-functional requirements such as cell penetration and binding strength to the solid metal. In tensile tests, Young's modulus and the strength of the SS foam were 4.0 GPa and 11.2 MPa respectively, which is comparable with human cancellous bone.     

Compressive behaviour of closed-cell aluminium foams at high strain rates

It has been well established that ALPORAS® foams is a strain rate sensitive material. However, the strain rate effect is not well quantified as it is not unusual for strain rate to vary during high speed compression. Moreover, according to previous research, aluminium foams, especially ALPORAS® foams, behave differently at low and high strain rates. Therefore, different plastic deformation mechanisms are expected for low and high strain rate loadings as a result of micro-inertia of cell walls. In this paper, the strain rate effect on the energy dissipation capacity of ALPORAS® foam was investigated experimentally by using a High Rate Instron Test System, with cross-head speed up to 10 m/s. The compressive tests were conducted over strain rates in the range of 1 × 10^?3 to 2.2 × 10² s^?1, with each test being at a fairly constant strain rate. An energy efficiency method was adopted to obtain the densification strain and plateau stress. The effect of strain rate and the foam density was well presented by empirical constitutive models. The experimental data were also discussed with reference to the recent results by other researchers but with different range of strain rates. An attempt has been made to qualitatively explain the observed decrease of densification strain with strain rate.     

Stretching behaviors of entangled materials with spiral wire structure

The entangled materials with spiral wire structure have been investigated in terms of the stretching behavior, mechanical properties, and stress–strain hysteresis effect. The results indicate that these materials are much more flexible than that with non-woven wire structure. They exhibit 1.05 MPa yielding strength and 5.7 MPa Young’s modulus in average at the porosity of 60%, and 2.47 MPa yielding strength and 12.3 MPa Young’s modulus in average at the porosity of 45%. Under tensile loading the materials exhibit a unique stress–strain behavior that goes through a long strain period after yielding and follows a quick stress increase on the stress–strain curve due to the ‘unclosing’ and ‘straightening’ mechanism of the spiral wire structure. In addition, these materials exhibit obvious stress–strain hysteresis effect. Their energy dissipation values determined according to the stress–strain hysteresis loops are 28.6 mJ/cm³ at the porosity of 60% and 102.3 mJ/cm³ at the porosity of 45%, which are much larger than that of the polymer foam, implying their promising applications for the energy absorption.     

Microstructure and properties of the Si3N4/silica aerogel composites fabricated by the sol–gel method via ambient pressure drying

Si₃N₄ particle reinforced silica aerogel composites have been fabricated by the sol–gel method via ambient pressure drying. The microstructure and mechanical, thermal insulation and dielectric properties of the composites were investigated. The effect of the Si₃N₄ content on the microstructure and properties were also clarified. The results indicate that the obtained mesoporous composites exhibit low thermal conductivity (0.024–0.072 Wm^− 1 K^− 1), low dielectric constant (1.55–1.85) and low loss tangent (0.005–0.007). As the Si₃N₄ content increased from 5 to 20 vol.%, the compressive strength and the flexural strength of the composites increased from 3.21 to 12.05 MPa and from 0.36 to 2.45 MPa, respectively. The obtained composites exhibit considerable promise in wave transparency and thermal insulation functional integration applications.     

Full-field shear analyses of sandwich core materials using Digital Image Correlation (DIC)

Mechanical properties and global stability of foam core sandwich structures are highly controlled by the shear response of the core material. In this work, we have studied the shear deformations of three common structural core materials with the aid of full-field optical analysis. The chosen core materials are namely extruded PET foam (ρ = 105 kg/m³, G_xz = 21 MPa,) and cross-linked PVC foam (ρ = 60 kg/m³, G_xz = 22 MPa) which have comparable shear properties, as well as Balsa wood with the lowest density commercially available (ρ = 94 kg/m³, G_xz = 106 MPa) as a reference core material. Both global and local shear strains in the core materials are calculated and graphically visualized. In the elastic region, foam cores showed more uniform deformations than Balsa. Yielding and shear failure of the two foam core materials were quite different. The PVC foam experienced a high local deformation under the load introduction bars, from which sub-interface shear failure initiated. The PET foam, in contrast, showed no sign of stress concentrations, resulting in a homogenous evolution of shear deformations in the mid-core regions. A comparison between the direct foam shear test and sandwich specimen bending suggested that the former method might not be capable of capturing a full picture of the in-service core shear response.     

Effects of solids loading on microstructure and mechanical properties of HfB2–20 vol.% MoSi2 ultra high temperature ceramic composites through aqueous gelcasting route

HfB₂–20 vol.% MoSi₂ ultra high temperature ceramic composites were prepared through aqueous gelcasting route. The stability of HfB₂ and MoSi₂ suspensions were studied by zeta potential measurements, sedimentation tests and apparent viscosity measurements. The solids loading had significant effects on the green and sintered densities, microstructure and mechanical properties of HfB₂–MoSi₂ composites. The values of flexural strength of the green and sintered bodies ranged from 18.3 to 38.7, and 111.5 to 415.9 MPa, respectively, which were strongly dependent on the solids loading. The values of fracture toughness of the sintered bodies ranged from 2.18 to 4.24 MPa m^1/2. The highest relative density, mechanical properties and the most homogeneous microstructure was obtained when the solids loading was 45 vol.%. The highest green strength, flexural strength and fracture toughness were 38.7 ± 5.3 MPa, 415.9 ± 17.0 MPa and 4.24 ± 0.22 MPa m^1/2, respectively.     

Development of rigid bio-based polyurethane foam reinforced with nanoclay

Integration of organic nanoclay into bio-based polyurethane (PU) foam is a promising alternative to enhance the foam’s properties via green technology. In this paper, modified diaminopropane montmorillonite (DAP-MMT) nanoclay was introduced into palm oil-based PU foam at different weight loadings, namely, 0, 2, 4, 6, 8, and 10 wt.%, in order to investigate the effects on the mechanical and thermal properties of the foam. Several tests and characterizations were carried out to study the surface morphology, density, compressive strength and thermal stability of the foam. It was found that foam exhibited an exfoliated or intercalated microstructure based on the DAP-MMT contents. The X-ray diffraction analysis showed that below 4 wt.%, the foams displayed exfoliated structures while beyond the value, the foams exhibited the intercalated morphologies. Closed cells with different cell sizes were observed when the DAP-MMT contents were varied. Meanwhile, thermal stability and compressive strength of foams increased with increasing DAP-MMT contents up to 4 wt.%, as shown by thermogravimetry analysis and compression test, respectively.     

Effect of heat-treatment on stress relief and dimensional stability behavior of SiCp/Al composite with high SiC content

In this paper, the effects of heat treatment processes on microstructure, residual stress and dimensional stability of 70 vol.% SiC_p/Al composites were investigated by using a field emission gun scanning electron microscope (SEM), the X-ray stress analyzer and the thermal cycling test method. The results showed that the matrix of the as-cast composite is in compression. After the solution-quenching (SQ), aging and thermal-cold cycling (TCC) treatment, the residual stress was reduced due to the plastic deformation of the matrix. With the increase in the numbers of the SQ treatment, the long rod Al(MnFe)₃Si₂ phase and the blocky CuAl₂ phase decreased while the spheroidization of these intermetallics increased. The TCC treatment refined the size of these intermetallics. As the number of the TCC treatments is increased, the resistance to micro-plastic deformation of the composite was also enhanced. The composite, which experienced the three-step SQ and aging and 12 times TCC treatment, presented the optimum thermal stability. Its hysteresis strain achieved 0.26 × 10^− 5, and remained constant during the second and third cycling tests. The excellent dimensional stability shows a promising potential to be used as mirror materials for preparing mirror substrates in industry.     

Fabrication of metallic composite foam using ceramic porous spheres “Light Expanded Clay Aggregate” via casting process

Composite metal foam was produced as an advanced porous material, using gravity casting technique. Light Expanded Clay Aggregate “LECA” was used as space holder for the produced composite metal foam. The used LECA density was 0.33–0.43 g/cm³ and the volume fraction of its porosity was from 73 to 88 vol.% and aluminum A355.0 was selected as matrix in order to produce the composite foam. Structural characterization, relative density, hardness and compressive test were studied. The composite metal foam was well investigated and found to have homogeneous structure, relatively equal pore, distributable pore and isotropy properties. The study resulted in that relative density, yield strength and energy absorption capacity were 0.44, 35.9 MPa and 18 MJ/m³, respectively.     

Development of rubberized syntactic foam

This study explored a novel hybrid syntactic foam for composite sandwich structures. A unique microstructure was designed and realized. The hybrid foam was fabricated by dispersing styrene–butadiene rubber latex coated glass microballoons into a nanoclay and milled glass fiber reinforced epoxy matrix. The manufacturing process for developing this unique microstructure was developed. A total of seven groups of beam specimens with varying compositions were prepared. Each group contained 12 identical specimens with dimensions 304.8 mm × 50.8 mm × 15.2 mm. The total number of specimens was 84. Among them, 42 beams were pure foam core specimens and the remaining 42 beams were sandwich specimens with each foam core wrapped by two layers of E-glass plain woven fabric reinforced epoxy skin. Both low velocity impact tests and four-point bending tests were conducted on the foam cores and sandwich beams. Compared with the control specimens, the test results showed that the rubberized syntactic foams were able to absorb a considerably higher amount of impact energy with an insignificant sacrifice in strength. This multi-phase material contained structures bridging over several length-scales. SEM pictures showed that several mechanisms were activated to collaboratively absorb impact energy, including microballoon crushing, interfacial debonding, matrix microcracking, and fiber pull-out; the rubber layer and the microfibers prevented the microcracks from propagating into macroscopic damage by means of rubber pinning and fiber bridge-over mechanisms. The micro-length scale damage insured that the sandwich beams retained the majority of their strength after the impact.     

Microstructure,mechanical and bio-corrosion properties of Mn-doped Mg–Zn–Ca bulk metallic glass composites

The effects of Mn substitution for Mg on the microstructure, mechanical properties, and corrosion behavior of Mg_69 ? xZn₂₇Ca₄Mn_x (x = 0, 0.5 and 1 at.%) alloys were investigated using X-ray diffraction, compressive tests, electrochemical treatments, and immersion tests, respectively. Microstructural observations showed that the Mg₆₉Zn₂₇Ca₄ alloy was mainly amorphous. The addition of Mn decreases the glass-forming ability, which results in a decreased strength from 545 MPa to 364 MPa. However, this strength is still suitable for implant application. Polarization and immersion tests in the simulated body fluid at 37 °C revealed that the Mn-doped Mg–Zn–Ca alloys have significantly higher corrosion resistance than traditional ZK60 and pure Mg alloys. Cytotoxicity test showed that cell viabilities of osteoblasts cultured with Mn-doped Mg–Zn–Ca alloys extracts were higher than that of pure Mg. Mg_68.5Zn₂₇Ca₄Mn_0.5 exhibits the highest bio-corrosion resistance, biocompatibility and has desirable mechanical properties, which could suggest to be used as biomedical materials in the future.     

Microstructure and mechanical properties of thixoformed A319 aluminium alloy

Thixoforming is a viable technology for forming alloys in a semisolid state into near net-shaped products. In the present study, the effect of a thixoforming process on the microstructure and mechanical properties of A319 aluminium alloy was investigated. The ingots obtained from the cooling slope were thixoformed in a press after they remained at 571 °C for 5 min, yielding a microstructure predominantly composed of α-Al globules and inter-globular Si particles. Some of the thixoformed samples were treated with an ageing process (T6) and then, hardness and tensile samples were prepared from the as-cast, as-thixoformed and thixoformed T6. All the thixoformed samples were characterised using optical microscopy, scanning electron microscopy (SEM), energy dispersive X-ray (EDX) and X-ray diffraction (XRD) as well as hardness measurements and tensile tests. The results indicate that the mechanical properties of the thixoformed A319 alloy increased after the T6 heat treatment (hardness of 124.2 ± 3.2 HV, tensile strength of 298 ± 3.0 MPa, yield strength of 201 ± 2.6 MPa and elongation to fracture of 4.5 ± 0.3%). The fracture samples from the tensile test were analysed, revealing that the iron-rich intermetallic observed in the samples reduced the tensile strength and ductility of the thixoformed A319 alloys.     

Al3Ni2–Al composites with nanocrystalline intermetallic matrix produced by consolidation of milled powders

Mechanically alloyed nanocrystalline Al₆₃Ni₃₇ powder with a metastable structure of NiAl phase was mixed with 20, 30 and 40 vol.% of Al powder. The powder mixtures as well as pure powder of Al₆₃Ni₃₇ alloy were consolidated at 600 °C under the pressure of 7.7 GPa. The bulk materials were characterised by structural investigations (X-ray diffraction, light and scanning electron microscopy, energy dispersive spectroscopy), compression and hardness tests and measurements of density and open porosity. During the consolidation, the metastable NiAl phase transformed into the equilibrium Al₃Ni₂ intermetallic. The mean crystallite size of the Al₃Ni₂ intermetallic in the bulk materials is below 40 nm. The microstructure of the composite samples consists of Al₃Ni₂ intermetallic areas surrounded by lamellae-like Al regions. The hardness of the produced Al₃Ni₂–Al composites is in the range of 5–6.5 GPa (514–663 HV1), while that of the Al₃Ni₂ intermetallic is 9.18 GPa (936 HV1). The compressive strength of the composites increases with the decrease of Al content, ranging from 567 MPa to 876 MPa. The plastic elongation of the composites was increasing with the increase of Al content, while the Al₃Ni₂ intermetallic failed in the elastic region.     

Titanium foam with coarser cell size and wide range of porosity using different types of evaporative space holders through powder metallurgy route

Ti-foams were made using different evaporative types of space holders such as acrowax and ammonium bicarbonate with a wide range of porosities (55–89%) through powder metallurgy technique. Cold compaction pressure was varied from 100 to 200 MPa in order to examine the effect of cold compaction pressures on the absolute porosities of the foams. The cell size, cell wall thickness and porosities of the foams were characterised as a function of cold compaction pressures and type of space holders. Empirical correlation has been established to predict foam porosities from compaction pressures and volume fraction of space holder. The sintered foams were found to be free from residue of the space holder. However, approximate 8–10% of titanium oxidized during sintering. The foam made with acrowax, as space holder attains slightly higher strength, modulus and energy absorption.     

FE modeling of the compressive behavior of porous copper-matrix nanocomposites

Compressive mechanical test and numerical simulation via finite element modeling have been employed on closed-cell copper-matrix nanocomposite foams reinforced by alumina particles. The FE analysis' purpose was to model the foam deformation behavior under compressive loading and to investigate the correlation between material characteristics and the compressive mechanical behavior. Exploring this, several foam samples with different conditions were manufactured and compression test was carried out on the samples. Scanning electron microscopy and image analysis have been performed on the foam samples to obtain the required data for the numerical simulation. The stress–strain curves exhibited plateau stress between 18 and 112.5 MPa and energy absorption in the range of 20.03–51.20 MJ/m³ for the foams with different relative densities. The foams exhibited enhanced mechanical properties to an optimum value, as a consequence of increasing the reinforcing nanoparticles, through both experimental tests and numerical simulation data. Also, the validated model of copper-matrix nanocomposite foams has been used to probe stress distribution in the foams. In addition, the results obtained by numerical simulation via ABAQUS CAE finite element modeling provided support for experimental test results. This confirmed that FEM is a favorable technique for predicting mechanical properties of nanocomposite copper foams.     

Effect of strain rate on cushioning properties of molded pulp products

Molded pulp product is widely used in distribution chains as a cushioning packaging of industrial products due to its favorable cushioning capability. How to evaluate the cushioning capability of molded pulp product is the key issue many scholars are interesting in. The load carrying capacity and energy absorbing of the molded pulp products used in the cushion packaging of mobile phones both in the static compression and dynamic impact were investigated in this paper by applying the experiment and finite element analysis. The static compression was conducted with the compression speed of 12 mm/min corresponding to the nominal strain rate 3.8 × 10⁻³ s⁻¹, and the dynamic impact tests were conducted with three drop heights of 25, 50 and 80 cm corresponding respectively to the nominal strain rates 4.2 × 10¹, 6.0 × 10¹ and 7.5 × 10¹ s⁻¹. The high speed camera was used to record the dynamic impact process and deformation. The finite element model of molded pulp product was built, and the stress and displacement nephograms, the dynamic impact deformation process, the load–displacement curve and the energy absorption curve of the molded pulp product were archived. The comparison between the finite element analysis and the experiment was made. The load–displacement curve of the finite element analysis is in agreement with that of the experiment in the static compression, and the energy absorption curves of the finite element analysis with different nominal strain rates are in agreement with that of the experiment in the area of the point of optimum energy absorption. However, a growing gap between the finite element analysis and the experiment appears with the nominal strain rate increasing, which may be induced by the use of the static stress–strain curve of the material in the finite element analysis of dynamic impact. The molded pulp product experiences the process from structural deformation, local stress concentration, first local buckling, redistribution of stress, global buckling, to structural dilapidation and densification. Two obvious buckling processes occur because of its complicated structure and two layers in structure. However, some additional local buckling also occur before the global buckling of structure in the case of dynamic impact with higher nominal strain rate. The deformation processes of molded pulp product from the finite element analysis and the experiment recorded by high-speed camera are coincident. With the nominal strain rate increasing, the yield stress of molded pulp product increases obviously, and the shoulder point of the energy absorption curve moves upward to the right. The yield stress under the dynamic impact at a drop height of 80 cm increases 59.4% compared with that under the static compression, and the corresponding optimum energy absorption increases 85.4%. The effects of strain rate on the load carrying capacity and the energy absorption of molded pulp product are remarkable. The results can be applied to the design of molded pulp products.     

Titanium foam through powder metallurgy route using acicular urea particles as space holder

In the present work, Ti foam has been synthesized employing powder metallurgy route. Irregular titanium powder particles were used as the matrix and acicular urea particles as the space holder. The distribution of the urea particles in the matrix of the compacted mass was observed to be fairly uniform. Pore morphology and compressive behavior of the resulting foam have been studied. The processed foam consisted of acicular porous regions of size up to 500 μm. The porous regions contained a large number of micro-pores along with the occasional presence of coarse pores, the latter thought to be unhealed portions of the original acicular pores. The foam delineated a distinct plateau region with plateau stress of 275 MPa and energy absorption capacity of 55 MJ/m³.     

Microstructure control of TCP/TCP-(t-ZrO2)/t-ZrO2 composites for artificial cortical bone

In this study, bone like continuously porous TCP/TCP-(t-ZrO₂)/t-ZrO₂ composites with a central channel were fabricated using a multi-pass extrusion process and their mechanical properties and microstructure at different sintering temperatures were investigated. Hydroxyapatite (HAp) powder was used as the raw powder which undergoes a phase transformation into the α-tricalcium phosphate phase (α-TCP) at a sintering temperature of 1500 °C. The external diameter and inside cylindrical hollow core were approximately 10.3 mm and 4.8 mm, respectively. The frame region contained numerous microchannels that extended from one side of the fabricated body to the other. The channeled frame region had a multi-layer microstructure with a TCP/TCP-(t-ZrO₂)/t-ZrO₂ layer configuration. The inner layer consisted of TCP, which make the wall of the microchannel. The material properties were characterized and microstructural analysis was carried out. The maximum pore size, compressive strength, and relative density of the fabricated system were approximately 86 μm, 53 MPa, and 77% when sintered at 1500 °C. The composites exhibited excellent biocompatibility and cell proliferation behavior resulted in the MTT assay and cell adhesion test using osteoblast-like MG-63 cells.