Quasi-static Compressive Loading Conditions Research Articles

Enhancing crashworthiness characteristics of modified hexagonal honeycomb structural panels through stretching and bending of ribs

The effects of stretching and bending of concave, convex, and horizontal ribs on the energy absorption characteristics of modified hexagonal honeycomb structural panels are investigated under in-plane quasi-static compression loading conditions. In this regard, five hierarchical modified structural panel configurations were fabricated using polylactic acid material (PLA) via a fused filament 3D printer, ensuring uniform wall thickness in the 1.5–2 mm range. The panels included the regular hexagonal panel (RHP), regular hexagonal panel with concave rib (RHCP), regular hexagonal panel with convex rib (RHXP), regular hexagonal panel with concave and horizontal ribs (RHCRP), and regular hexagonal panel with convex and horizontal ribs (RHXRP). In-plane quasi-static compressive loading tests were conducted to analyze crush resistance characteristics, and buckling modes of the modified honeycomb panels were examined through experimental and finite element analysis procedures. The result indicates that the specific energy absorption capacity (SEA) of RHXRP is increasing significantly compared to the SEA capacity of other categories of the structures. The changes in failure modes and increased crush energy absorption characteristics of modified RHP with the introduction of concave, convex, and horizontal ribs are elaborated.

Mechanical characterization of filled elastomer nanocomposites under finite-deformation cyclic loading using yield-surface-free plasticity

We elucidate and quantify the feasibility of an environmentally friendly alternative to the carbon-black-filled elastomer nanocomposite. Specifically, elastomer nanocomposites with three different fillers are studied (namely carbon-black, silica-silane-DPG, and silica-silane-hexylamine systems) and experimentally tested under two quasi-static compressive loading conditions (namely monotonic loading and cyclic loading at different large strain levels and without preconditioning). By restricting attention to the mechanical response of the composites, we utilize a finite-deformation yield-surface-free elastoplastic constitutive material modeling to characterize the mechanical response of the filled elastomers and, thus, elucidate the relationship between model parameters and nanocomposite composition. In turn, effects from different deformation and damage mechanisms are decoupled and quantified. The constitutive model is mechanistically sound and, after proper parameter identification, it yields an excellent agreement between experimental data and model response.

Anisotropic Compressive Behavior of Metallic Foams under Extreme Temperature Conditions.

Metallic foams find their applicability in complex systems that operate under both real-life conditions (Earth living conditions) and extreme temperature conditions (low or high temperatures). In this paper, the main mechanical properties of closed-cell aluminum alloy (A356) foams under quasi-static compression loading conditions were determined. In order to investigate the compressive behavior, three orthogonal directions (X, Y, and Z) and three testing temperatures (−196, 25 and 250 °C) were considered. It has been observed that the temperature significantly influences the strength properties and energy absorption performances of the aluminum metallic foams AMFs. Moreover, it was found that microstructural characteristics, such as intrinsic defects (intracellular cavities, micro-pores and thin cell-walls) and structural anisotropy (shape, size and orientation of cells), play a decisive role in the mechanical behavior of AMFs. Moreover, the paper compares the relative percentage change (relative percentage increase and decrease) of the main normalized compressive properties (yield stress, plateau stress, densification stress and the energy absorption) of AMF samples, according to testing temperature and loading direction.

Design of Functional Gradient Porous Structure and its Fabrication using DMLS Process

The functionally graded material (FGM) is referred as the material which is non-uniform and has changing structure and material composition. FGMs are now being used in different types of areas that are different from the initial area of application. A functional gradient porous structure is designed and modelled as prototype to validate for the mechanical and biomedical applications. In this work, gradient porous structure of Gyroid shape is used to design a model. Gradient porous structure is entirely different from the homogenous porous structure but like homogenous porous structure, it reduces material consumption with maintenance of similar strength. To fabricate the model, stainless steel 316L is used, which is a biomaterial. The effect of functional gradient on the compressive strength of the structures by considering nine different porosities (porosities = 10%, 20%, 30%, 40%, 50%, 60%, 70%, 80%, 90%) both experimentally and numerically, is studied. The initial stage involved the development of mathematical model of functionally gradient porous structure based on governing equation of Gyroid, which is a triply periodic minimal surface. CAD models of normal porous and gradient porous structures are generated using K3DSurf and Rhinoceros software. Developed structures are manufactured by Direct Metal Laser Sintering (DMLS) Additive manufacturing method with stainless steel 316L as the build material and experimentally tested under quasi static compressive loading conditions. These models are analyzed in ANSYS software. The CAD model is validated by comparing the experimental and numerical results and the Deviation between yield stress from experimental and numerical results obtained was 3.5%.

Direct Observation of Failure in Ice-Templated Ceramics Under Dynamic and Quasistatic Compressive Loading Conditions

The current study investigated the effects of porosity, microstructure, and strain rate regime on the damage evolution and failure behavior under uniaxial compressive loading conditions in ice-templated alumina materials. The compressive response was investigated in dynamic and quasistatic loading regimes. Microstructural analysis revealed that in the high porosity regime, morphology was lamellar. In the lower porosity materials processed at higher freezing front velocities (FFVs), morphology was dendritic but transitioned to lamellar structure with the decreasing FFV. Ice-templated materials with higher porosity exhibited progressive crushing type damage evolution, irrespective of the FFV and strain rate regime. The origin of progressive crushing type failure was observed to be the absence of macroscopic crack evolution in the vicinity of peak stress, and subsequent to peak stress damage evolved only in the form of minimal fragmentation that gradually increased with the increasing strain. However, at comparable strain, the extent of dynamic damage was less compared to quasistatic damage, which suggests enhanced resistance to brittle fracture at high-strain rates. With the decreasing porosity damage evolution process changed, particularly under quasistatic loading in the materials processed at higher FFVs. Up to peak stress materials were intact, whereas upon reaching peak stress significant damage evolved causing complete loss of compressive load-bearing capacity. Whereas, damage evolution under dynamic loading in the vicinity of peak stress was significantly limited and damage accumulated progressively with the increasing strain, which strongly suggests greater structural stability in the ice-templated porous ceramic materials at high-strain rates.

Mechanical and Microstructural Characterization of an AZ91⁻Activated Carbon Syntactic Foam.

In this study, activated carbon (AC) particles were combined with AZ91 alloy to manufacture a magnesium syntactic foam. This novel lightweight foam has a very low density, in the range of 1.12–1.18 gcm−3. The results show that no chemical reaction occurred between the AZ91 matrix and the activated carbon particles. The mechanical properties of the foam were evaluated under quasi-static compression loading conditions, and showed a consistent trend for the energy absorption of the fabricated AZ91–AC syntactic foams. The deformation mechanism of samples was a brittle fracture mode with the formation of shear bands during the fracture of all samples.

Compressive deformation behavior and strain rate sensitivity of Al-cenosphere hybrid foam with mono-modal, bi-modal and tri-modal cenosphere size distribution

AlSi12Cu1Mg1 aluminium alloy-cenosphere closed cell hybrid foams with different kinds of cenosphere size distribution (mono-modal, bi-modal and tri-modal) are used to see the effect of cenosphere size distribution on their deformation behavior under quasi static compressive loading conditions at different strain rates. The stress strain curves are almost similar type irrespective of the cenosphere size distribution and strain rate. However, the plateau stress and energy absorption increased significantly when one used bi-modal and or tri-modal cenosphere size distribution instead of mono-modal cenosphere size distribution. These plateau stresses and energy absorption also increased marginally with strain rate. The densification strain remained almost invariant with strain rate and cenosphere size distribution. The strain rate sensitivity and strain rate sensitivity parameter is relatively lower in case of bi-modal and tri-modal cenosphere size distribution particularly at higher relative density.

Prediction of Crashworthiness for Extruded Magnesium Materials

To assess the crashworthiness of simple wrought magnesium structures, the axial deformation behaviour of different square tubes produced from magnesium alloys AZ31 and ZE10 were numerically investigated under quasi-static compressive loading conditions. Finite-element simulations were conducted to predict and assess the plastic buckling and crush behaviour. The necessary data to determine parameters for the plastic potential were taken from compression tests conducted along different orientations. The yield function Hill48 was selected, despite its inability to capture the strength differential effect. The modelling approach pursued is justified by considering the mechanical loading conditions, the fabrication process of the profiles and its implication on strain anisotropy, balancing achievable accuracy and computational efforts. The simulation results revealed that the material work hardening rates evidenced in uniaxial compression tests influenced the buckling modes as well as the energy dissipation.

Experimental and numerical crushing analyses of thin-walled magnesium profiles

In order to assess the crashworthiness of simple magnesium structures the axial deformation behaviour of different hollow rectangular profiles produced from wrought magnesium alloys Mg–3wt.%Al–1wt.%Zn–0.3wt.%Mn and Mg–1wt.%Zn–0.4wt.%rare earth mischmetal were investigated under quasi-static compressive loading conditions. Laser beam welding was applied to build the crush configurations from plane rolled sheets; indirect extrusion was used to manufacture seamless profiles. Numerical simulations were conducted to predict and assess the crush behaviour. The simulation results revealed that the material work hardening rates evidenced in uniaxial compression tests together with the cross section influenced the buckling modes as well as the energy dissipation. The performance of the magnesium profiles in terms of dissipated specific energy is better than that of aluminium profiles for small compressive displacements. However, for large displacements, shear-compressive failure limited the crush displacement and hence the energy dissipation. The weld itself did not influence the failure and the energy dissipation of the respective structure. For the alloy and process development of wrought magnesium, prospective improvements towards higher dissipated energy can be realised by increasing not only the strength but also the hardening rate of the material.

Mechanical response of hard bio-based PU foams under cyclic quasi-static compressive loading conditions

In this article, the influences of environmental conditioning and cyclic compressive loading on bio-based neat polyurethane and fiber reinforced composite foams have been studied. Within the context of this manuscript the term bio-based polyurethane foam is defined as any foam containing one or more renewable materials based on chemical components in their basic composition. The samples studied are blocks with side lengths ranging from 20mm to 80mm in size. In addition to investigating the mechanical material behavior of these materials, the rationale for the investigation was to develop and disseminate engineering knowledge of these materials and also to consider these materials as possible alternatives to fiberglass and/or other foam reinforcing additives. It was observed that environmental conditioning resulted in overall foam material degradation after the first cycle of loading. Energy absorption levels were higher in the first loading cycle for the unconditioned specimens, but after 50 loading cycles the foams exhibited almost identical responses approaching zero. The load bearing capacity was lower in both bio-based foams when environmental conditioning was present and dry heat conditioning contributed to a more significant impact than wet heat conditioning. Cyclic mechanical testing results indicated that the foams degrade significantly after the first loading cycle and the degree of degradation between consecutive cycles decreases as the compression continues. Moreover, scanning electron microscopy was conducted to observe cellular geometry and cell fracture. A further investigation illustrated that the low density foam without fiber proved to be more resistant to both mechanical loading and environmental conditioning compared to the high density foam with fiber. This finding indicates that the presence of the fiber within foams results in a reduction of mechanical performance when either environmental conditioning or a given amount of compression is applied.

Control of load/displacement responses of AA6061-T6 and T4 circular extrusions under axial compressive loads

Axial crushing of AA6061-T6 and T4 circular extrusions with variable wall thicknesses was completed under both dynamic and quasi-static loading conditions to investigate the capability of controlling the load/displacement responses of the extrusions. Circular specimens with a nominal original wall thickness of 3.175 mm, an outer diameter of 50.8 mm, and a length of 300 mm were considered. Variations of the wall thickness in the axial direction were completed by material removal from the extrusion sidewall prior to crushing tests. Cutters used in this research had a height of 20 mm and blade tip widths of 1.0 mm. A curved deflector was used to flare the cut petalled sidewalls and facilitate the cutting system. Results from the impact tests illustrated that an initial peak cutting force with a magnitude of 1.08–1.74 times higher than that for the quasi-static loading was needed to initiate the cutting deformation mode. After this transient cutting stage, the load/displacement responses were observed to be similar to that from the quasi-static tests except for some slight fluctuations resulting from a minor amount of material fracture which occurred on the petalled sidewalls. A lesser extend of material fracture was observed on the T4 temper specimens due to the work hardening material property of the T4 temper condition. The mean cutting force from the dynamic tests were determined to be in the range of 0.92–1.09 times the mean force from the corresponding quasi-static test. Control of load versus displacement responses of the extrusions under both impact and quasi-static compressive loading conditions was accomplished through the variation of the wall thickness along the axial direction of extrusions.