Compression Crush Research Articles

Experimental investigation of the behavior of UHPCFST under repeated eccentric compression

This paper investigates the mechanical behavior of ultra-high-performance concrete-filled steel tubes (UHPCFST) under repeated eccentric compression. A total of 30 UHPCFST specimens are designed, fabricated, and tested. The design variables include steel tube thickness, UHPC type, loading eccentricity and load pattern. Failure modes, force-axial shortening curves, section strain distributions, lateral deflection distributions, bearing capacity and stiffness are studied. Three failure modes, i.e., steel tube bulge, compressive crush and tensile crack of the UHPC infill are observed. Specimens with larger loading eccentricity and thinner steel tube are more likely to exhibit all the three modes. Subjected to eccentric loading, the compressive strength and stiffness of the UHPCFST increase significantly with the increase of steel tube thickness and UHPC strength. In the case of repeated loading, stiffness degradation is observed. Existing formulas for the N-M curve and the eccentric compressive capacity are evaluated against the test results. A formula for eccentric compressive stiffness is derived based on the parabolic function assumption. Additionally, an empirical model is introduced to describe the force-axial shortening relationship of the UHPCFST under repeated eccentric compression, which may be applied in practical design and analysis.

Research on the Deformation Mechanism of Railway Subgrade under Buried Strike–Slip Fault Dislocation

With the gradual densification of China’s railway network, more and more railways are inevitably crossing active fault zones. Creep dislocation and stick–slip dislocation of the fault zones can lead to uneven deformation and cracks in the railway subgrade, threatening the sustainability of the railway. Therefore, a model test and numerical simulation were used to analyze the deformation mechanism and sustainability of the subgrade and foundation induced by a strike–slip fault dislocation in a flat site under different angles between the subgrade and fault strikes. The test and simulation results show that (1) under the influence of strike–slip fault dislocation, the horizontal direction of the subgrade appeared to have an S–shaped displacement. The top surface of the subgrade appeared to have a vertical settlement. Further, tension–shear cracks and compression crush zones appeared on the subgrade’s surface. (2) When the angle between the fault and subgrade strikes increased, the subgrade’s uneven deformations induced by fault dislocation first decreased and then increased. The angle between the main tension–shear crack on the top surface of the subgrade and the fault strike showed a trend of increasing and then decreasing. In addition, the compressive stress along the subgrade strike decreased, while the tensile stress along the subgrade strike gradually increased. (3) The tension–shear cracks in the subgrade and foundation were spiral and converged to the basement strike–slip fault along the depth direction. This study provides a reference for the safe operation and sustainability of railways near faults.

Parametric design and performance evaluation of gyroid triply periodic minimal surface preparation by LCD photopolymerization

In this paper, the Gyroid triply periodic minimal surface is prepared by liquid crystal display photopolymerization technology, and 10 models of the periodic parameter T in [1/5, 2] are designed. Using the method of finite element method and experimental verification, when T = 1/3, there are fewer stress concentration areas on the Gyroid surface, the number of grids is moderate, the compression crush rate is the smallest, and the porosity error is reasonable. Through the microscopic morphology, it is found that the surface, after printing, forms gear shape and resin residue so that the actual volume is larger than the theoretical volume, and the porosity is minor. Keeping periodic parameter T = 1/3 and porosity of 50%, four kinds of Gyroid surface structures were designed by changing the parameter surface offset, wall thickness, offset thickness, and gradient arrangement. The effects of different loading directions on its mechanical properties, deformation behavior, and energy absorption were discussed through compression experiments. The results show that the vertical load is applied to form a fault zone from the upper left angle to the lower right angle of 45°, and the parallel load is applied to create a fault zone from the upper right angle to the lower left grade of 45°. When the load is used in the vertical direction, the energy absorption and energy efficiency of the surface offset Gyroid surface are the largest. When the load is applied in the parallel order, the energy absorption curves of the four structures change similarly, and the deformation amplitude of the wall thickness Gyroid surface during the compression process is relatively stable. The energy efficiency of gradient arrangement Gyroid surface increases fastest in the compaction stage.

Dynamic response of aluminium matrix syntactic foams subjected to high strain-rate loadings

This paper presents experimental work to characterise the dynamic behaviour of aluminium matrix syntactic foams subjected to compression, Split Hopkinson Pressure Bar and terminal ballistic impact tests as well as blast loading. Numerical models have also been developed to simulate the dynamic response of the composite foams. The effect of strain-rate on their compressive crush behaviour has been investigated, given that the rate-dependent characteristics of these materials are required for designing dynamically loaded structures. Characterisation of the behaviour of the foam under high strain-rate loadings and the identification of the underlying failure mechanisms were also undertaken to evaluate their effective mechanical performance. The results show that the aluminium syntactic foam is sensitive to strain-rate in terms of initial stiffness, peak stress and plateau stress and show a pronounced high-rate dependence at a strain rate above 1000 s-1. The concrete damage plasticity model with rate-dependent features were used to simulate the dynamic behaviour of the foams, with the failure modes being captured. The model was verified and validated against the experimental results, and predictions were made for the normal and oblique ballistic impact response. Overall, the level of agreement between the numerical simulations and the experimental results is encouraging.

Modeling of Cross-Laminated Timber (CLT) panels loaded with combined out-of-plane bending and compression

Rolling shear is one of the major concerns that significantly impact the performance of CLT walls if they are subjected to combined out-of-plane bending and compression loads. Because the effects of rolling shear and out-of-plane bending are coupled to each other, prediction of the load-carrying capacity of CLT wall is always a challenge for the design of CLT structures. Current design codes employ an Ayrton-Perry type interaction equation as the failure criterion to check the safety of a CLT panel loaded with combined bending and compression. Nevertheless, there is no model available to predict their load-carrying capacity. The presented work aims at developing an analytical model to predict the load-carrying capacity of CLT wall loaded with combined out-of-plane bending and compression. In total 12 five-layer CLT panels loaded with different initial load eccentricities were tested to investigate the failure modes. Observed during the test were two ultimate failure modes, i.e., compression crush on the concave side and tension rupture in convex side. Based on these failure modes and deeming the test member as a beam-column, an analytical model which takes rolling shear effects into account to predict the load-carry capacity of CLT compression-bending members was developed. An explicit formula based on compression failure mode was proposed. The model is capable of determining the distribution of rolling shear stress along longitudinal direction, rolling shear-induced axial force and moments in CLT beam-columns. By calculating the load-carrying capacities of the specimens tested in this study as well as the additional three- and seven-layer specimens tested by another studies, it was found that the compression failure mode-based formula can provide good agreements with the test results.

Comparison and validation of computational methods for the prediction of the compressive crush energy absorption of CFRP structures

The crushing response of fiber-reinforced composite structures under compressive loading is investigated experimentally and then simulated using two damage models implemented in ESI Virtual Performance Solution explicit solver. The conventional Ladevèze continuum damage is compared to the recently implemented Waas-Pineda model, which uses non-local damage approach: virtual cracks are embedded with prescribed traction-separation laws and direct input of modal fracture energies.Initially, characterization tests of a unidirectional carbon fiber/epoxy tape are carried out to implement material card data and elementary simulations are performed for calibration. In a second stage, quasistatic crush compression of reference coupons are used for validation and numerical results are compared to experimental data in terms of specific absorbed energy.Results show that the Waas-Pineda model is easier to set up than the Ladevèze one and it also better reproduces the experimental results. The Ladevèze model underestimates the sustained crush stress since some damage modes could not be well identified from coupon testing of brittle material.

Numerical Simulation on the Compression Property in Different Face Sheet of Sandwich Panel Combined with Aluminum Foam

Sandwich face sheets are very important roles in composite materials. It was simulated that the quasi-static compressive crush performances of three types of sandwich sheets by ANSYS/LS-DYNA software. The aluminum top panels (“half hard”) had the higher plateau stress and its absorption energy reached 20.483J/mm3, were superior to the steel top panel (“hard”); the bottom face sheet rarely affects the energy absorption properties in cases.

Compressive Crush Performance of Square Tubes Filled with Spheres of Closed-Cell Aluminum Foams

AbstractThis paper describes the compressive crush behaviour of spheres of closed-cell aluminium foams with different diameters (6, 8 and 10 mm) and square tubes filled with these spheres. The spheres of closed-cell aluminium foams are net spherical shape fabricated via powder metallurgy methods by heating foamable precursor materials in a mould. The square tubes were filled by pouring the spheres of closed-cell aluminium foams freely (without any bonding). The compressive crush performance of square tubes filled with spheres of closed-cell aluminum foams were compared to that of the empty tubes. The results show a significant influence of the spheres of closed-cell aluminium foam on the average crushing load of the square tubes. The energy absorption in the square tube filled with spheres of closed-cell aluminium foam with diameters of 10 mm is higher than in the other square tubes. The spheres of closed-cell aluminium foams led to improvement of the energy absorption capacity of empty tubes.

Characterisation of direct 3D sand printing process for the production of sand cast mould tools

PurposeMetal casting industry is in recovery phase after the crisis in 2008; customer demand continues to increase, with 98.6 million metric tons cast in 2011. Traditional ferrous and non-ferrous casting techniques require one shot or permanent moulds which require tooling to produce. Tooling particularly for developmental projects can be costly and take valuable time to produce. Additive manufacturing (AM) has been used to manufacture sand patterns for metal sand casting using laser sintering and sand bonding. This research aims to focus on characterising the sand-bonded process developed by ExOne GmbhH Germany.Design/methodology/approachThe approach taken in this research is to evaluate characteristics of parts built in the build volume for dimensional accuracy, tensile and compressive crush strength, density, impact strength and high temperature resistance. These properties are required to compare the 3D sand printing (3DSP) process to direct laser sand sintering (DLSS) and traditional Furan-based casting sand mixtures. The samples were taken from a production machine over a period of 30 days to ensure consistency.FindingsThe 3DSP process has the capability to manufacture sand patterns to an accuracy of ±0.5 mm or error less than 0.3 per cent; it has also demonstrated the best build position to achieve accurate parts. The research has demonstrated the 3DSP patterns are comparable to traditional methods for important casting material characteristics such as tensile, compression and impact strength. It has been shown that the 3DSP process is capable manufacturing significantly larger parts, with build production rates up to 30 times higher compared to similar parts manufactured via the DLSS process.Research limitations/implicationsAs they has been very few 3DSP machines sold in Europe and particular UK, they has been little research into this new technique, and, therefore, they is a reliance on machine manufactures data for assessment. This research into 3DSP has increased the knowledge of this process significantly.Practical implicationsThis research would be of interest to designers and manufacturing engineers wishing to take advantage of the implications of having new design freedom, tool less manufacturing with short lead times in a wide range of materials using fundamentally tried and tested century’s old casting techniques.Originality/valueThe research for this paper revealed very little published academic research in this area; therefore, this work will increase the body of knowledge for this niche AM process.

Compressive behaviour of unconstrained and constrained integral-skin closed-cell aluminium foam

The aim of this paper is to evaluate the quasi-static and dynamic compressive crush performance of integral-skin closed-cell aluminium alloy foam with and without radial constraints. The foam specimens were prepared by the powder compact foaming method. The behaviour under different loading conditions (loading velocity and radial constraints) has been determined by an extensive experimental program. The results show a significant increase in the collapse stress of the integral-skin closed-cell aluminium foam under quasi-static loading when radial constraints are applied. The radial constraint induces a significant strain hardening of the foam, where the densification occurs at lower strains, consequently enhancing the energy absorption per unit volume of the deformed foam. The strain hardening is also sensitive to the foam density, increasing with the density.

Static and dynamic axial crush performance of in-situ foam-filled tubes

The aim of this paper is to study the quasi-static and dynamic compressive crush performance of newly developed in-situ foam-filled tubes (FFTs) made of light aluminium alloys prepared by powder compact foaming technique. By this method, the aluminium alloy empty tube is filled with an aluminium alloy foam during its formation. An extruded precursor of aluminium alloy and titanium hydride powder (0.5wt.%) has been used for this purpose. The axial mechanical crushing behaviour and the failure mechanisms were assessed by uniaxial compression tests coupled with infrared thermography. The axial crush performance of in-situ FFTs was compared with performance of the individual components (integral-skin foam and empty tubes) submitted to the same heat treatment used to prepare the FFTs. Results confirm that the in-situ FFTs have a more stable axial crush performance. The results also demonstrate that heat treated aluminium alloy structures ensure high ductility and very good crashworthiness since they deform without formation of cracks during compression, which is a pre-requisite for good and reliable crashworthiness behaviour.

Characterisation of aluminium alloy tubes filled with aluminium alloy integral-skin foam under axial compressive loads

Novel ex-situ foam-filled tubes (FFTs) were prepared by inserting an integral-skin foam filler into an empty aluminium alloy tube. The aluminium alloy foam filler is prepared by powder compact foaming technique allowing to combine the Al-alloy integral-skin filler with an Al-alloy tube which has not been studied yet. Axial compressive crush performance of the individual components (empty tubes and integral-skin foams) and FFTs was studied and evaluated using uniaxial compression tests, exploring their deformation and failure mechanisms. The FFTs deform by axisymmetric axial crushing mode (concertina mode) with the formation of a single visible concertina fold, but with the formation and propagation of longitudinal cracks. The results confirm an improved crush performance under axial compressive loads by introducing the integral-skin foam as a filler in empty tubes.

Modeling the Confinement and Prestress Effects on Dynamic Failure of Ceramic Deep Beam

The present study performs numerical experiments to investigate the confinement and prestress effects on the dynamic failure of a ceramic deep beam. Johnson-Holmquist ceramic model (JH-2) is implemented into LS-DYNA through its user subroutines. The implementation and the effectiveness of the model are validated by a single element compression test and available plate impact test results. Failure of ceramics is isolated into two modes, i.e. tension induced cracking and compression generated crushing. Three different setups, i.e. bare ceramic beam, the beam with lateral constraints, and the beam with lateral constraints and a 100 MPa pre-applied pressure are considered in the numerical experiments. The results show that, in lower velocity impact, few tension induced cracks connecting the impactor head and the supports happened on the specimen, minor crush zone is found around the supports. Under higher velocity impact, however, a relative larger crush zone is also observed near the impact head, spreading tension cracks occurred in a triangular zone on the specimen. The lateral confinement affects the tension induced failure under both lower velocity and higher velocity impacts. The pre-applied pressure has only minor effect on the failure of the deep beam in low velocity impact. In higher velocity impact, however, the pre-applied stress may change the distribution profile of the tensile cracks. Both pre-stress and the lateral constraints have negligible effect on the compression crush happened near the impactor head in the higher velocity impacts. The dynamic failure patterns of the ceramic deep beam and the confinement and prestress effects are demonstrated clearly in the present study. Energy transformation mechanism during the impacts is briefly discussed.

Analysis of Crushing Response of Composite Crashworthy Structures

The paper describes quasi-static and dynamic tests to characterise the energy absorption properties of polymer composite crash energy absorbing segment elements under axial loads. Detailed computer tomography scans of failed specimens are used to identify local compression crush failure mechanisms at the crush front. The varied crushing morphology between the compression strain rates identified in this paper is observed to be due to the differences in the response modes and mechanical properties of the strain dependent epoxy matrix. The importance of understanding the role of strain rate effects in composite crash energy absorbing structures is highlighted in this paper.

Failure mechanisms in energy-absorbing composite structures

Quasi-static tests are described for determination of the energy-absorption properties of composite crash energy-absorbing segment elements under axial loads. Detailed computer tomography scans of failed specimens were used to identify local compression crush failure mechanisms at the crush front. These mechanisms are important for selecting composite materials for energy-absorbing structures, such as helicopter and aircraft sub-floors. Finite element models of the failure processes are described that could be the basis for materials selection and future design procedures for crashworthy structures.

Transverse Compression Behavior of Softwood and Alternately Laminated Lumber of Rubberwood Veneer and Falcata Veneer

Softwood and alternately laminated lumber of rubber wood veneer and falcate veneer were compressed transversely. On the assumption that softwood and alternately laminated lumber are recognized as laminated composite structure of soft layer and hard layer, transverse compression strength of them are expected to be larger than that of lumber only of weaker layer (earlywood and falcate veneer). Cross section of transversely compressed softwood was observed using digital image correlation for strain analysis, and large shear strain has progressed on earlywood at edge of the softwood specimen. The cross section of the specimen after compression was examined under an incident-light microscope, so it was found that compression crush lines began on the boundary between earlywood and latewood at the edge of the specimen. It is probably because of shear stress generated at the boundary between soft layer and hard layer, that is, latewood of high-density would prevent earlywood of low-density from deforming under compression stress. However, when alternately laminated lumbers which are a similar structure to softwood were compressed transversely, shear strain was found not at the edge but at the inner part of the specimen. Moreover compression strength of alternately laminated lumber has been no larger than laminate lumber of falcate veneer. The area of large shear strain has formed inclined lines on the laminated lumber under compression stress, and the lines tended to coincident with checks formed by rotary peeling using a lathe. The lathe checks would mitigate the restriction of hard layer (rubber wood veneer), and so the alternately laminated lumber may not behave similar to softwood.

Prognosis and outcomes of hip fractures

In elderly patients with fractures, local complications at fracture sites of are relatively infrequent, whereas systemic complications commonly occur. There is a marked difference in anatomical features between femoral neck fractures and trochanteric fractures; neck fractures is an intracapsular fracture while trochanteric fractures are extracapsular fractures. In patients with a femoral neck fracture, bone strength at the site may diminish, leading to a compression crush of the bone, usually at least 1 year after the fracture. A survey performed in 10,992 Japanese patients with hip fractures has shown that 51% of these patients had been normal in daily living activities before suffering a fracture and this percentage decreased by 24% 1 year after the fracture. Mortality within 1 year after the fracture was 10%. The following prognostic predictive factors showed significant differences: dementia, pre-injury ambulatory capability, age, baseline serum albumin, baseline total protein, and baseline hemoglobin.

On the axisymmetric progressive crushing of circular tubes under axial compression

Moderately thick circular tubes under compression crush progressively by axisymmetric folding. The paper presents a combined experimental analytical study of the onset of collapse, its localization and the subsequent progressive folding. Results from four displacement controlled crushing experiments are presented on tubes of various radius-to-thickness ratios made of different metal alloys. The experimental results include the crushing response, careful measurements of the geometric characteristics of the folds and the mechanical properties of the alloys. A finite element model of the crushing process has been developed and results from simulations are directly compared with the experiments. The model is found to reproduce the crushing response to a significant degree of accuracy. The mean crushing load is essentially the same as in the experiments; the calculated wavelength of the folds are within a few percent from measured values as are other geometric variables considered. Thus, the crushing energy per unit length of tube is predicted to a very good accuracy. In addition, the model was used to demonstrate that changes in the loading cycles which take place as the number of folds increases, are due to small differences between the inner and outer folds which in turn affect the self contact of the fold walls. Three simpler models taken from the literature in which steady-state folding is modeled by kinematically admissible collapse mechanisms are critically reviewed by comparing predictions of key variables to measured values.

Compressive response and failure of braided textile composites: Part 1—experiments

Experimental results obtained by examining the planar biaxial compression/tension response of carbon 2D triaxial braided composites (2DTBC) are reported in this paper. These experiments were motivated by a need to examine the failure of 2DTBC in a state of stress that would be similar to what is experienced by the walls of a tubular member under compressive crush loads. Results obtained from a series of biaxial tests that were conducted with different proportional displacement loading ratio combinations of compression and tension are reported. In all cases, the dominant failure mechanism under such a stress state is the buckling of the bias and axial tows within the composite. Full field surface displacement data is acquired concurrently during all biaxial and some uniaxial tests using the technique of digital speckle photography. Digital images of the specimen surface that is illuminated with a He–Ne laser are acquired at discrete time intervals during the loading history using a high-resolution digital camera. These images are stored and analyzed to obtain the incremental inplane surface displacement field, Δ u( x, y) and Δ v( x, y). From these, the incremental inplane surface strains Δ ε x , Δ ε y and Δ γ xy are obtained by numerical differentiation. The present paper, which is the first in a two part series, is devoted to the biaxial experimental results pertaining to 2DTBC failure.

Upgrading ductility of RC beam-column connection with high performance FRP laminates

Strengthening and retrofitting of the reinforced concrete beams, which have been designed and built in the past, is one of the most important issues in structural engineering. In this study, reversal loading represents seismic excitation. The criterion for upgrading a RC joint against such loading is increasing its strength and ductility. Using composite fabrics does such enhancement. In this direction, FEM is adopted to analyze the problem, The non-linearity of concrete material, such as tension cracks and compression crush, are included. The steel bars behavior is considered as bilinear elasto-plastic, and Tsai-Wu criterion is used to control FRP failure. 8-Node solid element, 3-D link element, and layer shell element are used for modeling of concrete, steel rebar and FRP laminate, respectively, Both of the as-is and the retrofitted comer joints are subjected to quasi-static cyclic loading, and their performance is investigated and compared with each other, in terms of peak lateral load capacity, ductility, moment-rotation diagram, crack patterns and cracks width. The stacking sequence of FRP laminates is (45,45),, and it is made fi-om Glass/Epoxy materials. The results are presented in terms of load-deflection curves and hysteretic energy loops. The load-deflection curves, for both as-is and strengthened bearncolumn connections, are studied in details, and the influence of using the composite fabrics on continuity of joints, smearing the cracks and limiting their sizes, are considered. The behavior of retrofitted joints is significantly improved in terms of moment bearing capacity, ductility, axial load, and drift.