Compressive Response Research Articles

Experimental Investigations on the Mechanical Performances of Auxetic Metal-Ceramic Hybrid Lattice under Quasi-Static Compression and Dynamic Ballistic Loading

In recent years, there have been increasing research interests in investigating the compression and ballistic responses of metal-ceramic hybrid structures, mainly making use of the synergistic effects of conventional metal honeycomb structures and infilled ceramic matrix materials. In this paper, a novel hybrid auxetic re-entrant metal-ceramic lattice is designed and manufactured to overcome the intrinsic conflicts between the strength and toughness of architected mechanical metamaterials, synergistic effects of auxetic re-entrant metal honeycombs and infilled ceramic materials are experimentally and numerically studied, and auxetic deformation features and failure modes are characterized with the digital image correlation (DIC) technique as well. It was found that (1) the infilled ceramic matrix of conventional honeycomb frames only endure longitudinal compression or impact loading along the external loading direction, while auxetic metal re-entrant honeycomb components endure both longitudinal and transverse loading due to the negative Poisson′s ratio effect and (2) the collaborative effects of infilled auxetics and the constraint frames’ hybrid structure dramatically moderate the stress concentration state and improve the impact resistance of single-phase ceramic materials. Our results indicate that the auxetic hybrid design exhibits promising industrial application potentials for blast protection engineering.

The Compressive and Shear Characteristics of Miura-ori Forms as Core Materials of Sandwich Structures

The mechanical properties of Miura-ori foldcore metamaterials were studied using finite element simulations. The responses of foldcores with various topological parameters to quasi-static out-of-plane compression and shear loading were analyzed using the relative density as a governing parameter. The non-unique relationships between the core density and the materials’ strength in the examined loading directions were revealed, pointing out the strong influence of the Miura-ori topology. Linear relationships were established between the elastic moduli and relative densities of the Miura-ori metamaterials while power-law functions of the relative density with different exponent constants were established for the strength in different loading directions. It was shown that the Miura-ori materials possess the highest strength under shear in the {X}_{1}-{X}_{3} plane and it increases with the increase in the relative density. However, this characteristic is strongly influenced by the sector angle alpha . In general, the difference between the two shear strengths increases when increasing the relative density by using thicker cell walls. It is noted that the strength of the Miura-ori materials as a function of the relative density is nearly constant with respect to the cell dimensions if the values of folding angle {gamma }_{0} and sector angle alpha are given. The mechanical characteristics of the Miura-ori material with equal relative density, which exhibits the highest strength among the analyzed origami models, are compared with the out-of-plane compression and shear responses of prismatic hexagonal honeycomb. It is observed that compression and shear responses of the honeycomb outperform the Miura-ori foldcore in all loading directions when considering large deformations.

Compressing medical deep neural network models for edge devices using knowledge distillation

Recently, deep neural networks (DNNs) have been used successfully in many fields, particularly, in medical diagnosis. However, deep learning (DL)modelsare expensive in terms of memory and computing resources, whichhinders their implementation in limited-resources devices or for delay-sensitive systems. Therefore, these deep models need to be accelerated and compressed to smaller sizes to be deployed on edge devices without noticeably affecting their performance. In this paper, recent accelerating and compression approaches of DNN are analyzed and compared regarding their performance, applications, benefits, and limitations with a more focus on the knowledge distillation approach as a successful emergent approach in this field. In addition, a framework is proposed to develop knowledge distilled DNN models that can be deployed on fog/edge devices for automatic disease diagnosis. To evaluate the proposed framework, two compressed medical diagnosis systems are proposed based on knowledge distillation deep neural models for both COVID-19 and Malaria. The experimental results show that these knowledge distilled models have been compressed by 18.4% and 15% of the original model and their responses accelerated by 6.14x and 5.86%, respectively, while there were no significant drop in their performance (dropped by 0.9% and 1.2%, respectively). Furthermore, the distilled models are compared with other pruned and quantized models. The obtained results revealed the superiority of the distilled models in terms of compression rates and response time.

A novel hybrid lattice structure for improving compression mechanical properties

Lattice structures are widely used in load-bearing and energy-absorption applications for their lightweight, high specific stiffness, high specific strength and excellent energy-absorption. A novel hybrid lattice cell that combining octet cell and body-centered cube cell was proposed, and quasi-static compression experiments and finite element simulations were performed to investigate their energy-absorption characteristic and deformation mechanisms. The effects of the relative density, configuration of cell and component ratio sub-cell on the compression responses were also explored. The results showed that hybrid lattice improves compression modulus and yield strength by 10% and 16% maximally, respectively, and the energy-absorption of enhancement is 20% higher than the conventional lattices. In addition, the hybrid lattice can significantly alleviate the stress softening. By increasing the volume ratio of body centered cubic in the hybrid lattice structures, the energy-absorption can be improved. Under dynamic loading, the proposed hybrid lattice structures displayed outstanding normalized yield strength, which is superior to majority of porous structures. Inspired by the precipitation hardening mechanisms used in metallurgy to design high-performance alloys, two dual-phase lattices are developed. The quasi-static compression of dual-phase lattices shows three stages plateau stress and has a higher third stage than that of traditional dual-phase lattices. These findings provided design strategy for lightweight structure.

An experimental and computational investigation of embedded wrinkle’s impacts on the compressive responses of thick unidirectional glass fiber-reinforced composites

In thick unidirectional glass fiber-reinforced composites, the out-of-plane embedded wrinkle flaws have a major impact on compressive failure, which should be taken into account and assessed during the design, manufacturing, and inspection phases. The thick unidirectional coupons with embedded wrinkles of various severities were manufactured and tested. The deformation of the wrinkle region was captured by the Digital Image Correlation (DIC). As the wrinkle angle increased, the compressive failure stress decreases and the modulus does not change significantly, while the wrinkle amplitude has a negative effect on both the compressive failure stress and elastic modulus. The linear texture image regression approach is used to account for the path of fibers. The high-fidelity three-dimensional finite element (FE) models considering the real paths of the fibers are established. To reveal the interplay and impact of wrinkle severity parameters on the compressive failure behavior of composites, the progressive damage analyses and cohesive elements are also incorporated. Compared with the experiments, the FE studies accurately identify the dominant failure modes and failure stress values for various wrinkle severity parameters.

The Strain Rate Effects of Coral Sand at Different Relative Densities and Moisture Contents.

A 37-mm-diameter split Hopkinson pressure bar (SHPB) apparatus was used for impact loading tests to determine the effects of the relative density and moisture content on the dynamic properties of coral sand. The stress-strain curves in the uniaxial strain compression state were obtained for different relative densities and moisture contents under strain rates between 460 s-1 and 900 s-1. The results indicated that with an increase in the relative density, the strain rate becomes more insensitive to the stiffness of the coral sand. This was attributed to the variable breakage-energy efficiency at different compactness levels. Water affected the initial stiffening response of the coral sand, and the softening was correlated with the strain rate. Strength softening due to water lubrication was more significant at higher strain rates due to the higher frictional dissipation. The volumetric compressive response of the coral sand was investigated by determining the yielding characteristics. The form of the constitutive model has to be changed to the exponential form, and different stress-strain responses should be considered. We discuss the effects of the relative density and water content on the dynamic mechanical properties of coral sand and clarify the correlation with the strain rate.

Investigation of the compressive self-sensing response of filler-free metakaolin geopolymer binders and coatings

Self-sensing cementitious materials are an effective method of monitoring existing infrastructure due to their high durability and high sensing performance. Geopolymers are ideal candidates for such applications due to their enhanced ionic mobility, high mechanical properties and compatibility with ordinary Portland cement structures. In this paper, self–sensing filler-free metakaolin geopolymer binders and coatings are explored under repeated compression. Polypropylene fibers were added to the mix design to tackle shrinkage issues making these materials more suitable for site and field applications. The sensing performance of metakaolin geopolymers is examined under various loading patterns and their strain sensing performance is characterized. The geopolymer sensors displayed high repeatability and stability under different loading regimes over multiple cycles. The gauge factor for non-fiber and fiber geopolymer binders ranged from 18.3 to 38.3. Similarly, the gauge factor for geopolymer coatings ranged from 20.7 to 43.2. Based on the findings of this study, these materials have displayed the potential as a viable means of monitoring civil infrastructure under repeated compression.

Dynamic remodeling of fiber networks with stiff inclusions under compressive loading.

The ability of tissues to sustain and withstand mechanical stress is critical to tissue development and healthy tissue maintenance. The mechanical properties of tissues are typically considered to be dominated by the fibrous extracellular matrix (ECM) component of tissues. Fiber network mechanics can capture certain mechanical features of tissues, such as shear strain stiffening, but is insufficient in describing the compressive response of certain tissues and blood clots that are rich in extracellular matrix. To understand the mechanical response of tissues, we employ a contemporary mechanical model, a fibrous network of fibrin embedded with inert bead inclusions that preserve the volume-conserving constraints of cells in tissues. Combining bulk mechanical rheology and a custom imaging device, we show that the presence of inclusions alters the local dynamic remodeling of the networks undergoing uniaxial compressive strains and demonstrate non-affine correlated motion within a fiber-bead network, predicted to stretch fibers in the network and lead to the ability of the network to stiffen under compression, a key feature of real tissues. These findings have important implications for understanding how local structural properties of cells and ECM fibers impact the bulk mechanical response of real tissues. STATEMENT OF SIGNIFICANCE: To understand why real tissue stiffens under compression, we study a model tissue system which also stiffens: a fibrin network embedded with stiff beads. We design a device that images compression of both fiber and fiber-bead networks. Distinct from previous imaging studies, this setup can dynamically capture network deformation on scales larger than single fibers. From the videos, we see fluid flow and network remodeling are both critical to compression behavior. The fiber-bead network has faster fluid flow, reduced network recovery, and correlated motion during network relaxation. We hypothesize that the beads hinder network relaxation of stretched fibers, thus retaining the applied stress and exhibiting stiffening. Our findings reveal important details for modeling tissue mechanics towards optimizing healthcare.

Design of a Load Modulated Balanced Amplifier with a Two-Stage Control Power Amplifier

While an ideal Doherty power amplifier has a linear response, the load modulated balanced amplifier (LMBA) has a compressive response under ideal conditions. This inherent nonlinear characteristic is due to the lower power contribution of the single auxiliary device as the balanced amplifier transistors approach compression. This article presents an LMBA with a two-stage control signal amplifier in place of the single auxiliary device. The idea is to preserve a high and constant gain across the high- and low-power regions by tuning the two-stage gain control signal to match the balanced amplifier gain. An optimal load trajectory can be found for a high-efficiency design by appropriately terminating the second harmonic while ensuring an optimal impedance match in all devices. At the same time, by setting an optimal output power from the auxiliary device, sufficient power is provided to linearize the response of the main power amplifier beyond the output back-off power boundary. As proof of concept, a prototype is designed and implemented. The experimental measurements demonstrate a drain efficiency of 59%–64% at maximum output power and 46%–52% at 7.5 dB output back-off power over the target frequency range of 3.3–3.8 GHz.

Compressive anisotropy effects and crack evolution mechanisms of 3D5d braided composites induced by thermo-oxidative ageing

Ageing cracks and loading directions will affect mechanical behaviors of thermo-oxidative aged 3D braided composites. Here we report ageing crack propagations, compressive responses, in-situ strain evolutions, full-field damage distributions and crack evolution mechanisms of aged three-dimensional five-directional (3D5d) braided composites along out-of-plane (OP) and in-plane (IP) loading based on X-ray micro-computed tomography and digital image correlation technique. Ageing cracks are distributed at both axial ends that corresponding to the yarn arrangement and extend to the interior with the increase in ageing time. Compressive modulus, strength, retention rate and damage mode show ageing weakening behaviors and anisotropy effects. Strain distributions exhibit structure correlation. Ageing cracks affect the surface strain and damage distributions but not internal shear modes during OP loading. Yarn arrangement affects damage evolution and accumulation. Ageing cracks change the damage evolution path in both directions. The synergistic effect of ageing crack with IP loading is greater than that with OP loading. It is expected that this work can provide a clear guideline for the structural optimization and durability design of 3D braided composites.

Failure mechanisms in in-situ SEM micropillar compressions of pre-crystallized and crystallized zirconia-containing lithium silicate glass-ceramics

Microscale microstructure-property relations for zirconia-containing lithium silicate glass-ceramics (ZLS) are critical for their applications as load-bearing restorations. This study investigated in-situ scanning electron microscopy (SEM) micropillar compression responses of pre-crystallized and crystallized ZLS materials with a flat diamond punch. Micromechanical properties (moduli, strength, ductility, resilience and toughness) of the two materials were determined. Pre-crystallized and crystallized ZLS materials showed distinct ductile-brittle failure mechanisms. Pre-crystallized ZLS containing weaker lithium metasilicate crystals and higher concentrated glass matrix revealed its ductile mode featured with bending and delamination, and side-splitting fractures originated from fragmentation and microcracking. Crystallized ZLS with stronger lithium disilicate crystals and lower concentrated glass matrix demonstrated bending and shear-band initiation, shear fracture from shear-band expansion and fragmentation. Further, crystallized ZLS yielded much higher moduli, strength, ductility, resilience and toughness than pre-crystallized ZLS. This study provides vital insights into the basic understanding of micromechanical behavior of ZLS materials for load-bearing applications.

Infusible thermoplastic composites for wind turbine blade manufacturing: Static characterization of thermoplastic laminates under ambient conditions

The necessity for recyclable materials in wind energy applications has fueled research in glass fiber reinforced thermoplastic composites to replace their thermoset counterparts. Toward demonstrating that infusible acrylic resins can replace epoxy based composite systems in wind blade manufacturing, comprehensive static test protocols were performed, and the resulting data are presented. Specifically, unidirectional and biaxial (±45) continuous E-glass reinforced thermoplastic and epoxy laminates were prepared in four and eight ply laminates. Physical properties were characterized including density, fiber volume fraction, and glass transition temperatures, together with mechanical properties for tensile, compression, and shear responses. Comprehensive evaluation of these data supports infusible acrylic thermoplastic resin systems as viable alternative prospects to replace epoxies in E-glass reinforced wind blades as verified by comparable results for both composite systems.

Effect of lattice orientation on compressive properties of selective laser sintered nylon lattice coupons

As AM lattices become more popular in medical devices, it is important to consider how lattice design parameters affect the mechanical integrity and performance of a device. This research investigated the effect of lattice orientation on the compressive mechanical response of five common lattice geometries: Hexagonal Honeycomb (Hex), Diamond, Voronoi Tessellation Method (VTM), sheet-based Gyroid, and Face-Centered-Cubic (FCC). Samples were tested at two relative densities and eight orientations, printed in Nylon 12 (PA2200) on an EOS P396. The mechanical response was compared to simulated finite element analysis (FEA) response for Hex and FCC lattices. Hex lattices displayed significant orientation dependance. Diamond lattices demonstrated some orientation dependance when at a lower relative density. Gyroid, FCC, and VTM all displayed minimal orientation dependance. Increasing lattice relative density appeared to reduce anisotropy among tested orientations of all lattice geometries except Hex. FEA simulations were able to produce a trend response that matched the mechanical response trends based on the investigated orientations. These results support the need for multi axial lattice mechanical test considerations. It also bolsters the need for lattice FEA models to have a sufficient comparator when identifying “worst-case” lattice test scenarios.

Experimental and simulated study of 3D-printed couplings’ suitability for industrial application

This paper explores the possibility of applying reverse engineering to flexible coupling spare parts through additive manufacturing. Although couplings’ simplicity makes them go unnoticed, they connect elements that transmit power between two shafts, thus being an essential component for most of the machinery currently used in the industry. In this study, flexible couplings with different infill density (60% and 80%) were 3D printed by the fused filament fabrication technique. The original and the additive manufactured couplings were modelled to compare their compressive response and energy-absorbing characteristics, and experimental tests were performed to validate finite element analysis. To derive an optimal material distribution within coupling structure, a generative design approach was conducted through nTopology software. With this novel simulation-driven design, it is possible to reduce the weight of the redesigned part up to 15.8% by defining the wall thickness of the internal structure based on the results of finite element simulation, while maintaining its functionality. Moreover, an economic-environmental study was carried out. Results ensure that the 3D printed prototypes are suitable for replacing the original one under its current operating conditions. Additionally, the economic study shows that the redesigned couplings allow companies to save more than €2700 per coupling in relation to CO2 emission payments.

Role of the solidification cells on the yield strength of the Al-Si-Mg alloy manufactured using laser powder bed fusion: A micropillar compression study

To ascertain the role of the solidification cell structures on the mechanical performance of Al-Si-(Mg) alloys processed using the laser powder bed fusion (LPBF) technique, micropillar compression tests were performed on LPBF Al-10Si-0.3Mg (AlSi10Mg). The alloy's microstructure consists of submicron-scale cellular structures, dense dislocation networks, and dispersed nanoscale Si precipitates. The stress-strain responses of the micropillars are devoid of pronounced serrations and the yield strength and work hardening behaviors are size-independent. A comparison of the micropillar compression responses of the LPBF AlSi10Mg, 316 L stainless steel and Inconel 718 alloy, and nano-and micro-crystalline alloys is made. In LPBF AlSi10Mg, the combination of dislocation networks and shear-resistant Si particles resist the dislocation motion significantly and enhance dislocation storage. This results in the cellular structure dominating the strength and plastic flow. These results show a pathway for designing high strength alloys via additive manufacturing.

An Investigation of Quasi-Static Compression and Shock Responses under a Pneumatic Exciter on Brittle Truss Lattice Structures Fabricated with a Vat Photopolymer Resin

Shock attenuation is a significant aspect of shockproof design. The aim of this study is to explore the use of lattice structures for shock isolation applications. Five lattice structures were fabricated using photopolymer resin and subjected to quasi-static compression tests under a universal testing machine and shock response tests under a pneumatic exciter. The quasi-static compression tests provided preliminary data on the lattice structure’s collapse modes, stress, strain, and energy absorption. The shock test results revealed that the responses from the lattice structures were complex convolutions of the frequency. Moreover, the collapsed mode under the compression experiment did not guarantee the same outcome as in the shock impulse experiment. Amongst the lattice structures, the face-centred cubic with cubic perimeter (FCC + CP) structure exhibited the poorest shock isolation properties, with an ability to absorb only approximately one-third of the shock compared to solid structures. On the other hand, the body-centred cubic with cubic perimeter (BCC + CP) structure showed the highest impulse response with average shock transmissibility, making it a viable option for applications requiring shock insulation. However, it should be noted that this data may only be applicable for high acceleration with low degrees of force, less than 300 N.

Novel Weigh-in-Motion Pavement Sensor Based on Self-Sensing Nanocomposites for Vehicle Load Identification: Development, Performance Testing, and Validation.

The development of the transportation industry has led to an increasing number of overloaded vehicles, which reduces the service life of asphalt pavements. Currently, the traditional vehicle weighing method not only involves heavy equipment but also has a low weighing efficiency. To deal with the defects in the existing vehicle weighing system, this paper developed a road-embedded piezoresistive sensor based on self-sensing nanocomposites. The sensor developed in this paper adopts an integrated casting and encapsulation technology, in which an epoxy resin/MWCNT nanocomposite is used for the functional phase, and an epoxy resin/anhydride curing system is used for the high-temperature resistant encapsulation phase. The compressive stress-resistance response characteristics of the sensor were investigated by calibration experiments with an indoor universal testing machine. In addition, the sensors were embedded in the compacted asphalt concrete to validate the applicability to the harsh environment and back-calculate the dynamic vehicle loads on the rutting slab. The results show that the response relationship between the sensor resistance signal and the load is in accordance with the GaussAmp formula. The developed sensor not only survives effectively in asphalt concrete but also enables dynamic weighing of the vehicle loads. Consequently, this study provides a new pathway to develop high-performance weigh-in-motion pavement sensors.

Effects of acetic, malic, and citric acids on the large deformation behaviors of fish gelatin gels.

This research was aimed to quantify the effects of acetic acid, malic acid, and citric acid (0, 0.5, 1.0, and 2.0 g/100 g H2 O) on the stress-strain responses of fish gelatin (FG) gels (2, 4, and 6.67 g/100 g H2 O) under uniaxial compression up to 68% of deformation. The first-order Ogden model fitted quite well for the compression responses of FG gels (R2 = 0.9909-0.9997). Protons from the acids played a key role on weakening the FG gel structures (gel rigidity, μ, decreased 11%-27%), as the μ values and pH values of FG gels were linearly correlated (R2 = 0.8240-0.9748), regardless of the acid type. The addition of an acid also resulted in a significant increase (p < .002) in the strain hardening capacity (α) of gels with 2 g FG/100 g H2 O. Both μ and α values of FG gels with higher gelatin concentrations were less affected by an acid partly due to their stronger buffering effects. The μ and α values of FG gels as affected by acids could not be fully explained based upon the pH changes, implying that the effects of acetate, malate, and citrate ions on the gel structure could not be ignored.

Dynamic compression behavior of TiZrNbV refractory high-entropy alloys upon ultrahigh strain rate loading

In this study, the dynamic compressive response behavior of a body-centered cubic (BCC) single-phase TiZrNbV refractory high-entropy alloy (RHEA) was investigated under impact at speeds of 313–1584 m s–1 using two-stage, gas-gun-driven, high-speed plate-impact experiments; recovery sample analysis; and theoretical calculations. The strain rate and pressure were approximately 107 s−1 and 5.07–29.37 GPa, respectively. The results showed that the TiZrNbV RHEA had a Hugoniot elastic limit of 4.12–5.86 GPa and a spall strength of 1.84–2.03 GPa. The initial yield strength of the alloy showed a strong strain-rate dependence and could be described by the modified Zerilli–Armstrong model, while the phonon-damping effect was the main reason for its high strain-rate sensitivity. Microstructural analysis showed that the dynamic deformation of the TiZrNbV RHEA was controlled by the dislocation slip, dislocation proliferation, intersection of the deformation bands, and grain refinement. The analysis also showed that the intergranular, transgranular, and mixed-type cracks dominated the spall failure of the material. The dynamic Hall–Petch effect and pinning from the lattice distortion led to high dynamic yield strength. The critical strain rate for the phonon drag effect was positively related to the relative atomic mass and local strain field of the metals. Within the experimental loading range, the RHEA showed good structural stability, and simultaneously, the theoretical calculation method for the equation of state based on a cold-energy mixture could accurately predict its shock-response behavior. The valence-electron concentration (VEC) had a direct effect on the shock-compression properties of the HEAs; higher VEC implied more difficulty in compressing the HEAs. The findings of this study provide insights into understanding the mechanical response characteristics of RHEAs under extreme conditions such as high-speed impact and ultrahigh strain-rate loading.

The compressive response of the filled Kelvin foam

Periodic unit-cell solutions are obtained for the finite-strain, elasto-plastic response of a filled closed-cell Kelvin foam in uniaxial compression. The closed-cell Kelvin foam has edges of equal length, and attention is focussed on the regular Kelvin foam with faces comprising regular hexagons and squares. The elongated Kelvin foam is also studied: its faces comprise elongated hexagons and quadrilaterals. Both the cell walls and core of the Kelvin foam are treated as elastic, ideally plastic von Mises solids. In the first part of the study, the core modulus and strength are sufficiently small for the core to behave as an inviscid, incompressible fluid. Filling of the closed-cell Kelvin foam, in regular or elongated form, with an inviscid, incompressible core elevates its yield strength slightly and stabilises the post-yield response against softening. In the second part of the study, the macroscopic modulus and strength of a filled closed-cell foam are determined as a function of core modulus and deviatoric strength. The deformation mode of the cell edges switches from a bending mode to an affine stretching mode when the core is sufficiently stiff and strong; an analytical model is derived for affine deformation of cell walls and core. Finally, the response of a finite specimen containing an edge imperfection is in good agreement with the periodic, unit cell response of the filled Kelvin foam.