Compressive Loading Tests Research Articles

Mechanical properties evaluation and behaviour of cellulose-HDPE composite

Cellulose is the most abundant material of all the available natural polymers. Cellulose is a very light weight material which shows good strength and stiffness in its base form. And it has the properties like bio degradability, easy availability, environmental-friendly and good mechanical properties. Cellulose is mainly used in making of papers and fibers. Apart from this cellulose is also used in making the bio polymer-based composites using different synthetic strategies. Here, in this project we are going to prepare a composite from cellulose and plastic. Generally, there are composites with low cellulose content are easily accepted and widely used. But we are going to prepare a composite with high Cellulose content. Cellulose is extracted by chemical process from plants. Then by using this extracted cellulose, a high cellulose content composite is made by combining with HDPE. Three different compositions of cellulose and plastic i.e., [Cellulose50%, HDPE50%], [Cellulose45%, HDPE45%], [Cellulose40%, HDPE60%] are being used. We also study the mechanical properties and water absorption properties of this component in detail by performing tests like Tensile load test, Compression load test, Shear load test, and Hardness. The main aim of this project is to study the mechanical properties and to display emerging applications of Cellulose-plastic Composites.

A field study on the load sharing behavior of a micropiled raft underpinned by a waveform micropile

A waveform micropile (WMP) uses the jet-grouting method to generate shear keys along the pile shaft for improving shaft resistance and cost efficiency. In this study, field loading tests were performed to characterize the load sharing behavior upon inclusion of a WMP in a group of four micropiles. First, single-pile compressive loading tests were conducted on three WMPs and five type A micropiles (MP). Subsequently, a group-pile loading test was performed on a piled raft comprising 2 × 2 MPs and a central WMP. The load–settlements, axial stiffnesses, and load transfer mechanisms of individual MPs were analyzed during the tests, including the short- and long-term effects of the axial stiffnesses of the MPs on the load sharing ratio of the micropiled raft. The single-pile loading test results revealed that the shear keys along the WMPs caused its bearing capacities and axial stiffnesses to be 1.5 times and 2–5 times higher than those of MPs, respectively. In the micropiled-raft loading test, the load sharing ratios of the MPs increased with their axial stiffnesses, and the highest load sharing capacity was exhibited by the WMP, which constituted 30% of the total load and 2–3 times that of MPs. Moreover, the influence of raft on the load-sharing capacity should be considered as well.

Performance of Eco Engineered Cementitious Composites Containing Supplementary Cementitious Materials as a Binder and Recycled Concrete Fines as Fine Aggregate

Engineered cementitious composites (ECC) mixtures demand a large cement content, which is detrimental to their sustainable development because mass cement production is hazardous to the environment and human health. Thus, this paper investigates the mechanical performance of eco engineered cementitious composites (ECC) under axial compressive loading and direct tensile strength tests. The eco ECC used in this investigation was comprised of cement, superplasticizer, fly ash (FA) or ground granulated blast furnace slag (GGBS), polypropylene (PP) fibre, water and recycled concrete fines (RCF). Two (2) eco ECC mixture series were designed and prepared. GGBS70 (70 percent GGBS + 30 percent cement), FA70 (70 percent Fly Ash + 30 percent cement), GGBS80 (80 percent GGBS + 20 percent cement), and FA80 (80 percent Fly Ash + 20 percent cement) are the four Cement-GGBS and Cement-Fly Ash combinations examined in this study. Also every combination had two different RCF percentages, R0.2 (0.2 percent RCF) and R0.4 (0.4 percent RCF). The main objective of this research is to determine the optimum mix design for eco ECC that contains supplementary Cementitious Materials (SCMs) such as GGBS or FA. Additionally, recycled concrete fines (RCF) were used as a substitute for sand. The influence of different cement replacement materials and RCF content on compressive and tensile strength was experimentally investigated. The inclusion of GGBS as a partial replacement of cement in the eco concrete mixture results in greater compressive strength than Fly Ash (FA). The test results revealed that increasing the RCF content in the ECC mixture resulted in higher compressive and tensile strength. When the sand to binder ratio was adjusted between 0.2 and 0.4, the compressive and tensile strength of the ECC mixture increased.

An investigation of Polyether Imide (PEI) toughening of carbon fibre-reinforced Polyether Ether Ketone (PEEK) laminates

Current thermoset composite material systems have relatively low interlaminar fracture toughness, leaving them vulnerable to impact damage. While thermoplastic based systems are considered to be tougher, toughness levels can be dependent on processing parameters. In this study, Polyether imide (PEI) film layers were added to carbon fibre-reinforced Polyether ether ketone (CF/PEEK) laminate layups prior to consolidation to enhance the interlaminar toughness at key ply interfaces. It was found that the addition of the PEI film improves the Mode I and Mode II interlaminar toughness of the laminate. Low-velocity impact tests were performed on the PEI toughened CF/PEEK laminates, as well as a baseline CF/PEEK laminate and a CF/PEEK laminate with PEEK film inserts, for direct laminate thickness comparison. For low energy impacts (10 J), associated with tool drop events, it was found that the PEI toughened panel performed best. However, the performance difference decreased as the impact energy increased. Ultrasonic scans indicated that PEI toughened CF/PEEK laminates exhibited a smaller damage footprint. Compression after impact (CAI) and Combined Loading Compression (CLC) tests revealed that although the PEI inserts reduce the laminate undamaged compressive strength, they exhibited higher relative residual strengths compared to the other laminates tested.

Is Nice knot suture comparable to wire for cerclage fixation? A biomechanical performance study

Cerclage fixation is a known orthopedic technique shown to be beneficial for circumferential augmentation when screw fixation cannot be used or is undesirable. However, ongoing advances in suture materials and knot techniques exist, and there is a paucity of evidence existing which evaluates comparisons between the two. The objective of this study was to investigate the strength and durability of cerclage fixation between the Nice knot suture technique and monofilament wire. Static displacement over time and compression load testing were analyzed. Compression testing was conducted with the Jamar Hydraulic Hand Dynamometer. Distraction testing was conducted using the Instron test system with its associated program. The Nice knot was tied using number 2 and number 5 FiberWire (Arthrex) and compared to monofilament wire. Clinical failure (displacement of 10 mm), absolute failure (opening of the knot or material failure), maximum compression achieved, and steady state compression maintained were the outcomes of interest. Double-stranded monofilament wire produces maximum consistent compression of 90 kg, followed by single-stranded monofilament wire (60 kg). Number 5 FiberWire has a higher maximum compression load than number 2 FiberWire (50 kg vs. 22 kg), but it is lower than that of the double-stranded monofilament wire constructs. When compared to the single-stranded monofilament construct, the number 5 FiberWire Nice knot is comparable (P < .05). Average steady state compression achieved after 10 minutes of resting showed double-stranded monofilament wire to be 65 kg compared to single- stranded monofilament wire at 42 kg, which when, compared to suture, number 5 FiberWire measured at 15 kg and number 2 FiberWire at 8 kg. Average tension results from Instron distraction testing showed the double-stranded monofilament wire construct was able to withstand greater forces up to a displacement of 6 mm, after which the number 5 FiberWire Nice knot was stiffer. Number 5 FiberWire shows the most linear tension relationship, revealing it more efficiently withstands elastic forces. Load to failure was higher in the number 5 FiberWire Nice knot construct than that in both the monofilament wire constructs. The modes of failure for the Nice knot were always at the knot suture interface rather than at the knot. We propose this suture technique to be a viable alternative method for cerclaging to fix upper limb long-bone fractures.

Cyclic compressive behavior of limestone and silicomanganese slag concrete subjected to sulphate attack and wetting-drying action in marine environment

Concrete in maritime structure is vulnerable to deterioration owing to external sulphate attack, which can be exacerbated by wetting-drying action (WDA), jeopardizing its resistance to cyclic loads such as wind, wave and earthquake actions. This study aims to investigate the compressive fatigue behavior of concrete exposed to sulphate attack and WDA in marine environment. Cyclic compressive loading test was conducted on concrete after 150 days of deterioration. The effects of sulphate attack and WDA, upper stress loading level and loading frequency on fatigue life, residual strain, variation of elastic modulus and post-cyclic compressive strength were investigated. The sulphate penetration profiles, volume change and mass change of concrete during the exposure time were also measured. In addition, the performance of limestone concrete and silicomanganese (SiMn) slag concrete was compared in the study. The sulphate ion was found to penetrate concrete up to a depth of 20 mm, with a maximum content of 1.72%–2.58% near the surface. The cyclic loading test showed that degraded concrete had 38.2% higher residual displacement and 1.4% lower modulus of elasticity than normal concrete. The sulphate attack and WDA weakened the concrete, reducing its fatigue resistance. SiMn slag concrete had a lower fatigue life, larger residual displacement and greater stiffness degradation than limestone concrete.

An improved material model for loading-path and strain-rate dependent strength of impacted soda-lime glass plate

The main purpose of this work is to develop a macro material constitutive model for inorganic glass response description under impact conditions. Firstly, the quasi-static and dynamic strength of soda-lime glass was obtained through uniaxial compression and combined compression-shear loading tests. The strain-rate and loading-path dependence of glass strength was observed from these experimental results. An improved model of impacted soda-lime glass plate was proposed based on the JH-2 model including the loading-path influence through an additional factor as a function of the Lode parameter. In commercial code Abaqus, the improved model is implemented through a user-defined material subroutine. Additionally, simulation of the static test, SHPB test, and impact test on glass specimens respectively is conducted to validate the model with updated material constants. The comparisons illustrate that the improved model of soda-lime glass provides better accuracy and efficiency predictions of glass responses at various loading conditions.

Settlement of bored piles with expander body system in lateritic soils

The Expander Body pile (EB) is a combination of a cast-in-situ pile method with an inflated, pump-grouted tip. The EB system's pioneering conjunction with the conventional drilling pile technique has improved work load, foundation security, cost reductions and abrupt displacements in lateritic, porous, unsaturated soils. The aim of this article is to analyze settlement estimates of bored piles equipped with the Expander Body System on tropical lateritic soil, using a deformability modulus obtained from laboratory and field tests. The piles were subjected to compression and uplift load tests. In addition, the estimates of the pile settlement are compared with the measured values, and the findings are discussed. The results strongly support that PMT and SPT tests present the optimal ratios between the measured and estimated settlements for both bored piles and bored piles with the Expander Body System. It can also be observed that CPT tests presented reasonable estimates for tensioned piles. Ultimately, it is verified that straightforward elastic models for the settlement assessment of bored piles can be used reliably in practice for piles equipped with the Expander Body System on tropical unsaturated soils.

Three-part humeral head fractures treated with a definite construct of blocked threaded wires: finite element and parametric optimization analysis.

BackgroundMini open reduction and percutaneous fixation of three-part humeral head fracture with blocked threaded wires has demonstrated functional results similar to locking plates or intramedullary nails but with significantly lower major complication rate. In the context of three-part humeral head fractures, we performed a parametric optimization through a finite element analysis of a recently published construct to verify if the encouraging clinical results can be supported by a more rigorous investigation from a mechanical viewpoint.Materials and MethodsThe 2-dimensional geometry of a three-part proximal humerus fracture synthetized with a system of blocked threaded wires was created. Tension/bending/shear and compression load tests were simulated. A parametric optimization analysis was performed considering four design parameters (height of wire couples; wire material; interdistance between two wires). Eighteen simulations were carried out. Additional analyses were performed also considering a varying diameter of the external rod.ResultsFour points where the largest gap occurs and three points associated with the highest stress concentration were considered. As per the tension/bending/shear loading, a slight gap increase was observed in two different points (8.494 μm; 7.540 μm), while a slight decrease was detected along the greater tuberosity fracture line (1.445 μm). The maximum von Mises stress up to 64.4 MPa was achieved in the humeral head. As per the compression loading, the gap increased along the greater tuberosity fracture line (1.445 μm; 7.545μm); the maximum von Mises stress attains the value of 64.42 MPa. The smallest gap distance (15.37μm) and the lowest von Mises stress (51.51 MPa) were obtained in two different alternative constructs. The diameter of the external rod had no significant effect.ConclusionsThe studied construct is biomechanically valid; it only allows micromovements (one-thousandth of the characteristic humerus size) that are not able to cause humeral head rotation and translation. Furthermore, the construct generates acceptable pressure stresses on sensible areas of the fractured humeral head. Compared to the original construct, we propose to space the pair of horizontal wires for the great tuberosity by at least 1 cm.

Study on mechanical behavior and damage process of concrete with initial damage under eccentric load

In order to analyze the influence of eccentric load on mechanical properties and damage process of concrete with initial damage, the eccentric load compression tests of concrete under different confining pressures were carried out with the help of PFC particle flow program. The results show that: the eccentric load does not change the relationship between peak stress, crack initiation stress and confining pressure of concrete under uniform load, but decrease the value of them. The peak stress increasing coefficient under uniform load is higher than that under eccentric load, and the peak stress increasing coefficient increases in a linear function with the confining pressure, and the increasing rate is approximately the same. Under uniaxial compression of eccentric load, a type I shear crack approximately parallel to the loading direction is formed, while under biaxial compression, a bending type shear crack with the lower tip of the initial crack as the inflection point is formed. The number of microcracks in concrete under uniform load and eccentric load can be divided into three stages: the calm period at the initial loading stage, the pre-peak expansion period from crack initiation point to peak point, and the rapid increase period after the peak.

Infrared thermography for detecting cracks in pillar models with different reinforcing systems

The overburden pressure is concentrated in the pillar in between twin tunnels and hence monitoring is required for the stability of the pillar. In this paper, an experimental study was conducted to understand the behavior of pillars by simulating unreinforced, concrete reinforced and steel rib reinforced pillars. In order to define the initial crack and propagation pattern in the pillar, the crack was detected by using an infrared thermal camera as well as strain gauges. In a pilot test with cylindrical gypsum samples, crack friction and crack opening were determined according to the temperature change pattern at the crack point. In the compressive load test of the unreinforced pillar, cracks occurred and propagated in the pillars. After the initial crack, having an instantaneous temperature increase of about 0.1 °C, the temperature increased by about 0.3 °C to 0.4 °C continuously. The differential temperature occurring at the crack in the concrete reinforced pillar is higher than that of unreinforced pillars due to the larger overburden pressure. Three types of crack propagation occur with different features depending on the location of crack occurrence in the concrete reinforced pillar. In the steel rib reinforced pillar, an arch is created by the steel rib and hence there was no failure in the pillar.

Compression Load Tests on Composite Foundations of Spread Footing Anchored by Helical Anchors

This study elucidates the compression behavior of a type of composite foundation of spread footing anchored by helical anchors. Three composite foundations were installed at a field site, and compression load testing was carried out on each foundation. Both the site conditions and the load tests were documented comprehensively. The compression load-settlement curves of composite foundations exhibit an initial linear-elastic segment, a curve transition, and a final linear region, and their capacities should be interpreted from the load-settlement curves. Five representative interpretation criteria (Chin, Terzaghi and Peck, slope tangent, tangent intersection, and L1–L2) were employed to determine the capacity of each foundation. Both the helical anchors and the footing share compression loadings on the composite foundation. Soil pressure cells at the center, near the edge, and at the corner of the footing represent a distribution from the lower, middle, and higher ranges of incremental soil pressures underneath the footing. Helical anchors underneath the footing approximately share 60%–80% of total load applied on the composite foundation pier, and higher compression resistance of a composite foundation can be obtained by increasing the footing embedment depth and the number of helical anchors underneath the footing.

Hygrothermal Ageing Influence on BVI-Damaged Carbon/Epoxy Coupons under Compression Load.

Composite materials usage in several industrial fields is now widespread, and this leads to the necessity of overcoming issues that are still currently open. In the aeronautic industry, this is especially true for Barely Visible Impact Damage (BVID) and humidity uptake issues. BVID is the most insidious kind of impact damage, being rather common and not easily detectable. These, along with the ageing that a composite structure could face during its operative life, could be a cause of fatal failures. In this paper, the influence of water absorption on impacted specimens compressive residual strength was studied. Specimens were impacted using a modified Charpy pendulum. Two different locations were chosen for comparison: Near-Edge (NE) and Central (CI). Accelerated hygrothermal ageing was conducted on impacted and reference nonimpacted coupons, placing them in a water-filled jar at 70 °C. Compressive tests were performed in accordance with the Combined Loading Compression (CLC) test method. A Dynamic Mechanical Analysis (DMA) was performed as well. The results showed the influence of hygrothermal ageing, as expected. Nevertheless, the influence of impact location on compressive residual strength is not clearly noticeable in aged specimens, leading to the conclusion that hygrothermal ageing may have a greater effect on composite compressive strength than the analysed BVI damage.

Multidirectional mechanical properties and constitutive modeling of human adipose tissue under dynamic loading

The mechanical behavior of subcutaneous adipose tissue (SAT) affects the interaction between vehicle occupants and restraint systems in motor vehicle crashes (MVCs). To enhance future restraints, injury countermeasures, and other vehicle safety systems, computational simulations are often used to augment experiments because of their relative efficiency for parametric analysis. How well finite element human body models (FE-HBMs), which are often used in such simulations, predict human response has been limited by the absence of material models for human SAT that are applicable to the MVC environment. In this study, for the first time, dynamic multidirectional unconfined compression and simple shear loading tests were performed on human abdominal SAT specimens under conditions similar to MVCs. We also performed multiple ramp-hold tests to evaluate the quasilinear viscoelasticity (QLV) assumption and capture the stress relaxation behavior under both compression and shear. Our mechanical characterization was supplemented with scanning electron microscopy (SEM) performed in different orientations to investigate whether the macrostructural response can be related to the underlying microstructure. While the overall structure was shown to be visually different in different anatomical planes, a preferred orientation of any fibrous structures could not be identified. We showed that the nonlinear, viscoelastic, and direction-dependent responses under compression and shear tests could be captured by incorporating QLV in an Ogden-type hyperelastic model. Our comprehensive approach will lead to more accurate computational simulations and support the collective effort on the research of future occupant protection systems. Statement of significanceThere is an urgent need to characterize the mechanical behavior of human adipose tissue under multiple dynamic loading conditions, and to identify constitutive models that are able to capture the tissue response under these conditions. We performed the first series of experiments on human adipose tissue specimens to characterize the multi-directional compression and shear behavior at impact loading rates and obtained scanning electron microscope images to investigate whether the macrostructural response can be related to the underlying microstructure. The results showed that human adipose tissue is nonlinear, viscoelastic and direction dependent, and its mechanical response under compression and shear tests at different loading rates can be captured by incorporating quasi-linear viscoelasticity in an Ogden-type hyperelastic model.

Influence of the specimen production and preparation on the compressive strength and the fatigue resistance of HPC and UHPC

The results of tests under monotonically increasing load and cyclic compression load are often analysed by means of probabilistic methods. Although there is a considerable scattering in the results, especially in the number of cycles to failure, the cause of these cannot be completely explained. The imperfections of the specimens tested are among the causes of this scattering mentioned in the literature. Based on a round robin test the influence of HPC and UHPC production and specimen preparation techniques on the mean values of the compressive strengths, number of cycles to failure and data scattering have been evaluated. The main findings of the study are that the production techniques have an influence on the compressive strength, however, do not affect the mean number of cycles to failure. Moreover, the accurate preparation of the specimens has a positive influence on the compressive strength and the scattering of the results of both compression and cyclic load tests. The mean number of cycles to failure of HPC specimens is not influenced by the preparation techniques, whereas the polishing technique may have a positive influence on the mean number of cycles to failure of UHPC specimens.

Conventional bicortical pin substitution with a novel unicortical pin in external fixation: A biomechanical study

IntroductionAs most patients with polytrauma or open fractures are converted from temporary external fixation to definite stabilization, the prevention of complications such as infection is especially important. To overcome the high risk of infection associated with the use of the conventional bicortical pin for temporary external fixation, the authors developed a novel unicortical pin and analyzed it in a biomechanical study. MethodsThe unicortical pin consisted of an inner screw, purchasing the cortical bone, and an outer sleeve with 6 spikes. A bicortical pin was used for the purpose of comparison. A fracture gap model was stabilized using a monoplanar configuration. Both the unicortical pins (Uni group) and bicortical pins (Bi group) underwent axial compressive and torsional load testing using a servo-hydraulic testing machine. Stiffness, load to failure, and mode of failure were documented. ResultsStiffness and load to failure of the Uni group (average, 40.5 N/mm and 1098.4 N, respectively) were greater than that of the Bi group (average, 33.7 N/mm and 968.6 N, respectively) in the axial compressive load test (P = 0.008 and 0.032). Stiffness and load to failure of the Uni group (average, 1.2 Nm/degree and 1.7 Nm, respectively) were also significantly higher than those of the Bi group (average, 0.8 Nm/degree and 0.6 Nm, respectively) in the torsional load test (P = 0.008 and 0.016). All pins in the Bi group were bent at the pin-synthetic bone interface without synthetic bone failure. Contrarily, the Uni group did not show any pin bending or failure. However, in the axial compression test, partial cracks in the synthetic bone were found at the interface with spikes in the outer shell. In addition, in the torsion test, incomplete fractures were seen through the inner screws' holes. ConclusionCompared with the conventional bicortical pin, the newly designed unicortical pin significantly increased fracture stability under both axial compressive and torsional loads. The unicortical pin can be considered an alternative biomechanical solution to obtain adequate stability when performing external fixation of fractures.

Research on Bearing Characteristics of Open-Ended Pipe Piles under Static Load

The accurate estimate of the ultimate bearing capacity of a single pile in the vertical direction is an important issue in the design of the pile foundation. This paper presents a static test on a single-pile model. The test was performed through a large-scale model casing test equipment that is independently developed. Various factors that affect the different test soil samples have been taken into account. In addition, the test has measured the pile’s internal stress and displacement through the sensors that were installed on the pile. What is more, a series of studies on the settling character of the single pile, pile lateral friction, changing nature of tip resistance, and its development with settling have been carried out. Finally, this paper analyzes the bearing capacity behavior and load transfer mechanism in the compressive static load test on the single pile in the vertical direction. The test results show that, under the same static load, the lateral friction of a pile in the sand is bigger than that in the silty clay, and with the increasing load at the pile tip, the increment speed of tip resistance in the silty clay is much faster than that in the sand, while pile’s bearing capacity in the sand is much bigger than that in the silty clay.

Application of Static Compression Load Test of Joint Piles in Seaport “Prorva” in the Caspian Sea Coastal Area (Western Kazakhstan)

Application of Static Compression Load Test of Joint Piles in Seaport “Prorva” in the Caspian Sea Coastal Area (Western Kazakhstan)

The study on stability of composite panel structure under axial compression load

The axial compressive load test and finite element simulation are made to study the mechanical properties of aircraft stiffened composite panel. Firstly, the numerical simulation model of composite stiffened panel structure is constructed, the accuracy and feasibility of the simulation model are verified by calculating the value of MAC (Modal Assurance Criterion) between the computational free modal and experimental free modal. Then, the nonlinear post-buckling numerical simulation is carried out to extract the buckling load, the post-buckling load path and the failure load. Then, the axial compression test of the panel structure is carried out by the testing machine, and the load-displacement curve and the load-strain curve of the loading position are obtained. Finally, the correctness of the analysis method is proved by comparing the numerical simulation value with the experimental analysis value. The experimental research method of the mechanical properties of the composite stiffened panel under axial load is explored, which can be used as a reference for the study of the bearing capacity of the stiffened panel.

Prototyping rail track for micro-people movers using additive manufacturing: Failure topology characterization

This paper describes the design and prototyping of railroad tracks for micro-people movers (MPM) using 3D printing technology. Electric MPMs have found applications for short distance travel needs. PLA (polylactide) is the choice of material for the prototyping in this paper. One of the advantages of using 3D printed railroad tracks is being able to properly address the rendering of a variety of topographic profiles of naturally occurring landscapes. The 3D printing of railroad track projects starts with digitally modelling the structure to integrate the automated manufacturing process. To determine the bearing capacity of the printed tracks, both compression and flexural load tests were conducted. The results, as anticipated, indicate that the load capacity and failure modes depend on the fiber content and layer directions of the 3D printed tracks. As the fiber content percentages increase from 20% to 100%, the failure modes transition from material-based control feature to a more structure-based control type. Because material contents are closely associated with the weight of the rail and the cost of production, design optimization can be made based on the correlation between load capacity and the failure mode.