Compressive Yield Research Articles

A Reliability-Based Design Approach for the Flexural Resistance of Compression Yielded Fibre-Reinforced Polymer (FRP)-Reinforced Concrete Beams

Fibre-reinforced polymer (FRP) reinforcement has been employed as an alternative to conventional steel reinforcement in concrete structures, which is attributed to its excellent strength and corrosion resistance. However, one drawback is that FRP reinforcements are brittle and affect the ductility of concrete structures. One of the recent effective techniques proposed to overcome ductility issues is the compression yielding (CY) concept. The CY mechanism allows the structure to fail differently than the conventional FRP-reinforced concrete structure. Thus, the existing design recommendations as per the current codes for FRP-reinforced concrete structures are not appropriate. Hence, reliability studies are crucial for the development of a functional CY beam design in order to emphasise the structure’s lifetime performance and to guarantee safety requirements. In this study, a reliability-based design approach is developed for a compression-yielded FRP-reinforced concrete beam (CY beam) using load and resistance factor design (LRFD). Firstly, the flexural failure modes of CY beams are discussed. The uncertainties involved in the development of the probabilistic model for the CY beam are defined. A case study is consequently conducted for a CY beam with random variables that are associated with the statistical characteristics of material properties and load. The reliability analysis method employed in this research is the Hasofer–Lind method. The results suggest the importance of choosing appropriate design variables and stochastic parameters for CY blocks that contribute to a higher level of reliability. The reliability index and resistance factors of a CY beam are then evaluated using the Monte Carlo Simulation computational method. The reliability index value of 3.336 is obtained from the simulation, which indicates that the CY beam demonstrates ductile behaviour. The results not only demonstrate ductile behaviour but also contribute to a possible reduction in material costs and a substantial safety margin. When compared to conventional FRP-reinforced concrete beams, for different load ratios, CY beams showed higher resistance and better reliability levels.

Reducing target reliability index of concrete bridge beams through compression yielding

Damage to reinforced concrete (RC) bridges due to accidental overloading is inevitable, especially for those that deteriorate over time due to various environmental and operational factors. When significant damage occurs, it needs to be replaced. However, replacing bridges is expensive and time-consuming. This problem can be well resolved by the concept of compression yield (CY) structures. When an overload occurs, the CY block in the beam is triggered like a fuse, forcing the beam to deform in a ductile manner, thus preventing further overloads. Additionally, the damaged CY blocks can be replaced without replacing the entire beam. Due to this safer failure mode and lower cost of failure, the safety reserve of the CY beam can be significantly lower than that of the traditional RC structure, which means that the target reliability of the CY bridge needs to be re-established. The objective of this study is to develop the target reliability of CY bridge. The target reliability of structures is determined through cost optimization. The life-cycle costs for bridges are determined based on the practical construction and post-construction management process. The calculated results indicate that although the initial cost of CY beams could be higher, the losses associated with failures are significantly lower compared to RC beams. Consequently, the target reliability and life cycle costs of CY bridge can be lower than those of the RC bridge.

Compressive Mechanical Behavior and Corresponding Failure Mechanism of Polymethacrylimide Foam Induced by Thermo-Mechanical Coupling.

Thermal-mechanical coupling during the molding process can cause compressive yield in the polymer foam core and then affect the molding quality of the sandwich structure. This work investigates the compressive mechanical properties and failure mechanism of polymethacrylimide (PMI) foam in the molding temperature range of 20-120 °C. First, the DMA result indicates that PMI foam has minimal mechanical loss in the 20~120 °C range and can be regarded as an elastoplastic material, and the TGA curve further proves that the PMI foam is thermally stable within 120 °C. Then, the compression results show that compared with 20 °C, the yield stress and elastic modulus of PMI foam decrease by 22.0% and 17.5% at 80 °C and 35.2% and 31.4% at 120 °C, respectively. Meanwhile, the failure mode changes from brittle fracture to plastic yield at about 80 °C. Moreover, a real representative volume element (rRVE) of PMI foam is established by using Micro-CT and Avizo 3D reconstruction methods, and the simulation results indicate that PMI foam mainly shows brittle fractures at 20 °C, while both brittle fractures and plastic yield occur at 80 °C, and most foam cells undergo plastic yield at 120 °C. Finally, the simulation based on a single-cell RVE reveals that the air pressure inside the foam has an obvious influence of about 6.7% on the yield stress of PMI foam at 80 °C (brittle-plastic transition zone).

A novel approach for designing efficient and sustainable cooling cycles with low global warming potential refrigerants

With the current legislation on the phase-out of 3rd generation refrigerants, new cooling cycles are expected to operate with 4th generation refrigerants, hence, the need for optimal system performance with these new working fluids. In this study, an innovative optimization approach was applied for the design of cooling cycles with 4th generation refrigerants based on integrating statistical analysis design of experiments (DoE) with molecular modeling using the polar soft-SAFT model. First, a detailed multi-criteria assessment was applied for the selection of 4th generation refrigerants in medium–low temperature applications. Results demonstrated the potentiality of trans-1,3,3,3-tetrafluoroprop-1-ene (R1234ze(E)) or cis-1,2,3,3,3-pentafluoroprop-1-ene (R1225ye(Z)) in terms of environmental, safety, and technical criteria in basic cooling cycles under specific operating conditions. Multi-objective optimization guided using statistical analysis tools were implemented to study potential enhancement in cooling cycle performance using these promising refrigerants in terms of energy and exergy efficiency. This included evaporator and condenser temperature, fluid choice, compression yield, superheating/subcooling degrees, and cycle type. The evaporation and condenser temperature, and the compressor efficiency are shown to monopolize more than three-quarters of the cumulative contribution on system efficiency for those operated with R1234ze(E) in advanced liquid-to-suction line heat exchangers (LL/SL-IHX). Further optimization through examining the effect of heat transfer phenomena assisted in determining optimal operating conditions for new systems operating with low GWP refrigerants, instilling annual cost savings of $1.59 K and reduction in CO2 emissions by 1.02 tCO2-eq compared to the baseline system.

Comparison of Shallow (−20 °C) and Deep Cryogenic Treatment (−196 °C) to Enhance the Properties of a Mg/2wt.%CeO2 Nanocomposite

Magnesium and its composites have been used in various applications owing to their high specific strength properties and low density. However, the application is limited to room-temperature conditions owing to the lack of research available on the ability of magnesium alloys to perform in sub-zero conditions. The present study attempted, for the first time, the effects of two cryogenic temperatures (−20 °C/253 K and −196 °C/77 K) on the physical, thermal, and mechanical properties of a Mg/2wt.%CeO2 nanocomposite. The materials were synthesized using the disintegrated melt deposition method followed by hot extrusion. The results revealed that the shallow cryogenically treated (refrigerated at −20 °C) samples display a reduction in porosity, lower ignition resistance, similar microhardness, compressive yield, and ultimate strength and failure strain when compared to deep cryogenically treated samples in liquid nitrogen at −196 °C. Although deep cryogenically treated samples showed an overall edge, the extent of the increase in properties may not be justified, as samples exposed at −20 °C display very similar mechanical properties, thus reducing the overall cost of the cryogenic process. The results were compared with the data available in the open literature, and the mechanisms behind the improvement of the properties were evaluated.

Lightweight Al3Ti-based medium-entropy alloys with well-balanced strength and ductility

The lightweight Al3Ti intermetallic compound shows superior properties at elevated temperatures but its room-temperature brittleness largely limits its usefulness. We propose Al3Ti-based lightweight medium-entropy alloys (MEAs) with selected alloying elements, which change Al3Ti from a tetragonal D022 structure to a ductile cubic L12 one with embedded hard B2 and D8a phases. A combination of improved ductility and strength can be achieved. Four lightweight AlTiCrMnFeCu MEAs (ρ=3.65∼4.27 g/cm3) with tunable balance between hardness and ductility were fabricated. Ti and Fe promoted the formation of hard B2 phase, while Cr and Mn favored the formation of D8a phase which strengthened the alloy at the minor expense of ductility. The compressive yield and peak strengths of the MEAs e.g., Al55Ti20Cr5Mn10Fe5Cu5, can reach as high as 650 MPa and 1366 MPa, respectively, with its fracture strain around 17 %. This study provides useful information for designing Al3Ti-based lightweight MEAs with desirable properties.

Study on Load–Slip Curve of a PBL Shear Key at a Steel–Concrete Composite Joint

The steel–concrete composite truss adopts a new type of steel-concrete composite joint with high rigidity and load-carrying capacity. In order to more conveniently and clearly grasp the working mechanism of Perfobond Leiste (PBL) shear keys in the core area of new composite structures such as steel–concrete composite trusses, the lack of strong theoretical support for the theoretical formula of load–slip relationships in the entire loading process of single PBL shear keys is solved. By proposing a straight–curved–straight three-stage simplified load–slip curve with respect to the PBL shear key, the stress process of the PBL shear key is divided into three stages—the elastic stage, plastic stage, and strengthening stage—based on the compressive yield and failure critical point of tenon concrete in the shear key. With reference to the calculation method of the bearing capacity of the order pile under horizontal loads and by calculating the shear stiffness of the shear key, a theoretical formula suitable for separating the load–slip relationship of a single PBL shear key in the entire loading process of the ear plate composite joint is proposed. The results show that, in the elastic section, the slope of the curve is related to the concrete reaction coefficient and the material parameters of the penetrating steel bar; moreover, in the strengthened section, the coefficient is related to the shear modulus of the penetrating steel bar, and a more uniform length distribution of the penetrating steel bar between the two joint plates will improve the initial stiffness of the PBL shear key to a certain extent. The results of the proposed method are in good agreement with the finite element results and experimental values. This research study’s results can provide a convenient design method for the design of the internal PBL shear keys of new composite structure joints, promoting the promotion and application of new composite structures and advancing the development of the engineering field.

Experimental study and analysis-oriented model of PET FRP confined ECC cylinders under monotonic axial compression

Recently, several compressive yielding (CY) materials have been developed to improve the flexural ductility of FRP bar-reinforced concrete members, regarding the lack of ductility of FRP bars. However, the currently developed CY materials involving or using steel were not ideal for structures exposed to marine environments. It still needs to develop the non-metal material having CY behavior. This study investigated the failure modes and mechanical properties of large rupture strain (LRS) FRP confined ECC under monotonic axial compression intending to develop it to achieve the demand of CY properties. The results demonstrated that LRS FRP jackets could significantly enhance the compressive ductility (as high as 16.27) of ECC compared to the conventional FRP confined concrete or ECC with the same confinement stiffness of FRP jacket. Moreover, the ductility of LRS FRP confined ECC could reach the ductility of existing CY materials. After developing the dilation model and actively-confined ECC stress–strain model developed based on the database, the analysis-oriented model for LRS FRP confined ECC considering load-path dependence was developed to design the LRS FRP confined ECC as the CY material.

Colloidal and Sedimentation Behavior of Kaolinite Suspension in Presence of Non-Ionic Polyacrylamide (PAM).

Colloidal behavior of kaolinite particles in water was investigated in this manuscript, without and with the addition of a polymer flocculant (non-anionic polyacrylamide (PAM)), using diverse imaging techniques in addition to LUMisizer. The addition of PAM was found to be causing the formation of bridges among particles thus increasing their settling rates to the bottom of the container. To assess the size of flocs and the potential morphology of PAM around particles and their clusters, the state of flocs formation and polymer distribution was analyzed through various microscopical techniques, namely scanning electron microscopy (SEM) and transmission electron microscopy (TEM). SEM and TEM results revealed that, in the absence of PAM, the floc structure of the sediment was loose and irregularly distributed, while the presence of PAM made the sediment structures greatly denser. Later, using LUMisizer, dynamic light scattering (DLS) and the zeta potential of kaolinite, sedimentation, and colloidal behavior of suspension came under scrutiny. Using LUMisizer, the maximum packing and settling rates of the particles were experimentally obtained as roughly 44 vol%; settling rates were estimated in 63-352 µm/s when centrifugal force varied and, using maximum packing values, compressive yield was estimated to vary between 48-94 kPa. The results of this study are instructive in choosing appropriate polymers and operating conditions to settle clay minerals in tailing ponds. Additionally, the maximum packing of kaolinite particles was simulated with spherical particles with varied polydispersity to connect DLS data to the maximum packing values obtained using LUMisizer; the little discrepancy between simulation and experimental values was found to be encouraging.

Machine learning-driven evaluation and optimisation of compression yielded FRP-reinforced concrete beam with T section

Fibre reinforced polymer (FRP)-reinforced concrete beams usually encounter brittle failure due to the linear behaviour of FRP. To solve this issue, compression yielding (CY) concept was proposed recently to improve the ductility of FRP-reinforced concrete beams. However, because of the complexity of the compression yielding mechanism, the calculation of flexural capacity and ductility of FRP-reinforced concrete beam with CY block (CY beam) is challenging, especially for the CY beam with T section due to the lack of closed form solution. In this study, an integrated model is proposed based on machine learning method to evaluate the moment capacity and ductility of the CY beam with T section. To improve the prediction accuracy of the artificial neural network model for moment capacity, different activation functions are tested. The section effectiveness of CY beam with T section is evaluated using the proposed support vector machine model, which combines different kernel functions. Gaussian process regression is then employed to predict the ductility of CY beam with T section. It demonstrates that the developed integrated model can produce highly accurate predictions. In addition, a genetic algorithm (GA) is developed for identifying optimal CY beam section design solutions. Finally, the robustness of the model in the optimisation design for the CY beams with rectangular section and T section is demonstrated by using two numerical examples.

Reliability-Based Design Analysis for FRP Reinforced Compression Yield Beams.

Fiber-reinforced polymers (FRPs) provide promising prospects for replacing steel bars in traditional reinforced concrete structures. However, the use of FRP as tension bars in concrete beams leads to insufficient ductility because of its elastic characteristics. A newly developed compression-yielding (CY) beam has successfully solved this issue. Instead of tensile reinforcement yield, the ductile deformation of a CY beam is realized by the compression yield of a CY block in the compressive region. Another important feature is that the CY block is also the fuse of the beam, where material damage to the beam is concentrated in the CY block region and can be easily replaced. As a load-bearing recoverable and ductile structure, it is necessary to conduct a reliability-based design analysis and recommend reduction factors for this new structure. In this study, the function for calculating the failure probability of CY beams is proposed, semi-probabilistic design recommendations are presented, and Monte Carlo simulation (MCS) is adopted as a reliability analysis method. This study discusses the influence of the possible characteristics of the critical variables on reliability and provides the reliability index with different reduction factors to guide the design of the CY beam. These analyses indicate that the reliability index can be improved from the material design of the CY block in greater strength fb, smaller depth, smaller coefficient of variation of fb, and yield modulus ratio ξ. This study also shows that compared with the design of FRP concrete beams, the ductile failure mode of the CY beams allows a lower safety factor to meet safety requirements, which significantly reduces construction costs and avoids over-designing the load-bearing capacity.

Numerical study on flexural behaviour of FRP reinforced concrete beams with compression yielding blocks

Fibre-reinforced polymer (FRP) bars are used in concrete structural members to tackle the corrosion problem of steel bars. However, the brittle rupture of FRP bars results in relatively low ductility of such concrete members. This paper numerically investigates the feasibility of using compression yielding (CY) block to enhance the ductility of FRP bar reinforced concrete beams. A finite element model is developed to study the behaviour of beam adopting the CY block, followed by a parametric analysis on the effects of material properties and geometry of the CY block. The results indicate that the adoption of CY block changes the failure mode of the beam from brittle concrete crushing to ductile compression yielding, increasing both the loading capacity and ductility of the beam. Increasing the compressive yield strength of the CY block can effectively increase the loading capacity but decrease the ductility of beams. A higher compressive ultimate strength of the CY block also increases the loading capacity but has limited effect on the beam ductility. In addition, the beam ductility can be increased by reducing the yielding and ultimate strains of the CY block, while the loading capacity can be enhanced by higher yielding strain or lower ultimate strain. It is revealed that sufficient height of the CY block is required to prevent concrete crushing in the compression zone, and an increase in CY block height improves the beam ductility. The CY block length should cover at least the pure bending zone when the section with the block has higher flexural capacity than that without the block, otherwise the length can be controlled as the theoretical plastic hinge length.

Perforated steel block of realizing large ductility under compression: Parametric study and stress–strain modeling

Abstract On one hand, the nature of linear elastic up to brittle rupture hinders the application of fiber-reinforced polymer (FRP) bars as reinforcement in the concrete member due to the displacement ductility demand of structures. On the other hand, FRP bars are equipped with many irreplaceable advantages as reinforcement in concrete structures. To resolve this contradiction, a possible solution is to use the so-called compression yield (CY) structural system and the ductility of a concrete beam incorporating a CY system comes from the compressive side rather than the tensile side. Thus, the development of material in the compressive side (CY material) with well-designed mechanical properties (strength, stiffness, and ductility) is a key challenge. In this study, the CY material is developed by perforating the mild steel block and then substantiated by the test results. Then, experimentally calibrated finite element models are used to conduct systematic parametric studies, based on which parametric equations are proposed to predict the stiffness and ultimate strength of the CY material. Finally, theoretical constitutive models are developed to predict the stress–strain response of perforated steel block under compression and a reasonably acceptable agreement is reached between the model predictions and the test results.

Perforated steel for realizing extraordinary ductility under compression: Testing and finite element modeling

Abstract One key obstacle restricting the application of fiber-reinforced polymer (FRP) bars from being used as reinforcement in structural concrete is the significantly reduced ductility because FRP under tension is linear elastic up to brittle rupture at small strain. Recently, a new structural concept, compression yielding (CY), has been proposed as a way to overcome the insufficient ductility of concrete structures reinforced with FRP bars or other non-ductile materials. In the CY structural system, the compression-zone of normal concrete is replaced by a ductile material within the plastic hinge. This enables the flexural deformation to be achieved by the compressive deformation of CY material rather than a tensile deformation of longitudinal reinforcing bars. To this end, an ideal CY material requires strength to be maintained during the extraordinarily large deformation process. This study tries to identify methods for developing this kind of CY material by designing and optimizing perforations inside a mild steel block. The effects of key parameters, including ratio, diameter, and arrangement of perforations on the stiffness, strength, and ductility of CY materials were experimentally investigated. In addition, a finite element (FE) model was developed to predict the behavior of the proposed CY material.

Effect of various niobium additions on microstructure and mechanical behavior of a NiAl–Cr–Mo eutectic alloy

Abstract The microstructure and compressive behavior of the NiAl – 28Cr – 6Mo alloy doped with various amounts of Nb have been investigated. The results show that the microstructure of all Nb-doped alloys mainly consists of three phases, viz. the gray lamellar Cr(Mo) plate, the black NiAl matrix, and Cr2Nb with C14-structure-type 1 Laves phase semicontinuously distributed at the cell boundary. All Nb-doped alloys exhibit relatively good room-temperature compressive ductility and higher yield strength at all temperatures compared to the NiAl – 28Cr – 6Mo eutectic alloy due to the presence of Laves phase. It is found that the NiAl – 28Cr – 6Mo alloy doped with 1 at.% Nb attains the optimum concerning high temperature strength and room temperature ductility.

Mechanical properties of an epoxy-based coating reinforced with silica aerogel and ammonium polyphosphate additives

Flame retardant (FR) additives may degrade polymers’ mechanical performance. In this work, FR epoxy composites fabricated based on two popular FR agents of ammonium polyphosphate (APP) and silica aerogel (SAG) are investigated. Several mechanical properties of these composites, including compressive, micro-hardness, and Izod impact, were investigated for different filler loadings. Although the addition of 10 vol.% APP improved compressive modulus, yield strength, and micro-hardness, it degraded the impact strength. The incorporation of SAG made the composites more ductile, improved the impact strength, but deteriorated their compressive properties. Samples containing both SAG and APP demonstrated synergetic effects evident by their enhanced compressive properties and hardness. The findings of this study can guide the design of epoxies with both exceptional FR and mechanical performance.

Evaluation of flexural resistance of compression yielded concrete beams reinforced with fibre reinforced polymers

Concrete elements reinforced with fibre reinforced polymers (FRPs) have been increasingly applied in civil engineering structures. However, these structural elements are usually suffering from brittle failure caused by either concrete crushing or the sudden rupture of FRP. To solve this common issue, a compression yielding (CY) mechanism was recently developed with the aim of enhancing the ductile behaviour of FRP-reinforced concrete beams. In the present study, the flexural resistance of FRP-reinforced concrete beam with a CY block in the compression zone (CY beam) is analysed, and a closed-form solution is derived for the moment capacity of CY beam. The influence of the uncertainties of the mechanical properties of CY material on the flexural resistance of CY beam are quantified. Engineering reliability analysis is then conducted to obtain the reduction factor for CY beam under different load combinations. A reduction factor of 0.75 for building structural members and 0.70 for bridge structural members are recommended for engineering design. In addition, a reduction factor table is provided considering a wider range of statistical parameters.

In Situ Grafted Composite Nanoparticles-Reinforced Polyurethane Elastomer Composites with Excellent Continuous Anti-Impact Performance.

Polyurethane elastomer (PUE) has attracted much attention in impact energy absorption due to its impressive toughness and easy processability. However, the lack of continuous impact resistance limits its wider application. Here, an amino-siloxane (APTES) grafted WS2-coated MWCNTs (A-WS2@MWCNTs) filler was synthesized, and A-WS2@MWCNTs/PUE was prepared by using the filler. Mechanical tests and impact damage characterization of pure PUE and composite PUE were carried out systematically. Compared with pure PUE, the static compressive strength and dynamic yield stress of A-WS2@MWCNTs/PUE are increased by 144.2% and 331.7%, respectively. A-WS2@MWCNTs/PUE remains intact after 10 consecutive impacts, while the pure PUE appears serious damage after only a one-time impact. The improvement of mechanical properties of A-WS2@MWCNTs/PUE lies in the interfacial interaction and synergy of composite fillers. Microscopic morphology observation and damage analysis show that the composite nanofiller has suitable interfacial compatibility with the PUE matrix and can inhibit crack growth and expansion. Therefore, this experiment provides an experimental and theoretical basis for the preparation of PUE with excellent impact resistance, which will help PUE to be more widely used in the protection field.

An investigation on twist extrusion followed by forward extrusion in production of aluminum–copper bimetallic bar

In this research, the feasibility of making aluminum–copper bimetallic bar by twist extrusion followed by forward extrusion is addressed. In this consecutive process, twist extrusion was used in several passes and its effect was investigated on the bond strength between aluminum and copper as well as the mechanical properties of the produced bimetallic bars. When forward extrusion was the only applied process, the compressive yield and shear bond strength of produced bimetallic bars were 184MPa and 5.4MPa, respectively. Applying four twist extrusion passes followed by one forward extrusion pass increased these values such that the compressive yield and shear bond strength were increased by about 64% and 200%, respectively. The hardness was also significantly increased by the utilization of this procedure. Microstructures of copper and aluminum in the produced bars showed that by applying and repetition of the twist extrusion, the grain size was reduced. The Mechanical locking was the main factor in bond formation. Reducing the gap between the metal plates at the interface and increasing the joint fraction improved the shear bond strength.

Rheological and mechanical properties of fibre-reinforced cemented paste and foam backfill

ABSTRACT The properties of fibre-reinforced cemented paste backfill (CPB) and foam backfill (FB) were investigated through bench-scale vane viscometer, mini-slump and compression tests. Samples of CPB (no air entrained) and FB (10, 20, 30, and 40% air by volume) were made with four concentrations of sisal, basalt, or Nanofibrillated cellulose fibres (0, 0.2, 0.5, and 0.8%). The results show that air entrainment decreased the unconfined compressive strength (UCS) and yield stress of FB, while the addition of the three types of fibre helped to compensate the UCS and built stronger internal bonds and sound structures, which led to different failure characteristics.