Tensile Conditions Research Articles

The theory of critical distances applied to fracture of rocks with circular cavities

This work presents experimental and theoretical analyses of the fracture behavior of different rocks containing circular holes subjected to uniaxial compressive uniform loads. The experimental critical loads are compared with those derived from the Theory of Critical Distances (TCD) and finite element simulations. The rocks being analyzed are Floresta sandstone, Moleanos limestone, Macael marble and Carrara marble. They were previously characterized under compressive and tensile conditions, obtaining their corresponding Poisson's ratios, Young's moduli and ultimate tensile and compressive strengths. Besides, their fracture properties, specifically their fracture toughnesses and critical distances, were also available from a previous experimental campaign on Single Edge Notched Beam specimens with different notch radii and tested under 4-point-bending conditions. In this paper, prismatic specimens (9 per each type of rock) containing a cylindrical cavity at their center were uniaxially compressed until failure. The fracture pattern was revealed and agrees with previously published cases. The TCD, specifically the Point Method, was applied with the aim of comparing the corresponding fracture load predictions with the experimental ones. Three-dimensional finite element analyses were used to calculate the stress fields. The application of the TCD on the Floresta sandstone and the Moleanos limestone provides reasonable predictions of fracture loads, given their linear-elastic behavior. For the two studied marbles, the resulting predictions are overly conservative despite their quasi-brittle behavior. This may be attributed to complex process zones with intense microcracking that are revealed as white patches prior to failure and generate dust and small fragments after failure.

Influence of Post-Processing Conditions on the Microstructure, Static, and Fatigue Resistance of Laser Powder Bed Fused Ti-6Al-4V Components

The microstructure, static, and fatigue mechanical properties of laser powder bed fused (LPBF) Ti-6Al-4V components subjected to three different post-processing treatments (PTs) are compared. The first treatment includes stress relief (SR) and beta-phase annealing (BA) heat treatments, the second one includes SR, beta-solution (BST) and over aging (OA) heat treatments, and the third procedure is a combination of hot isostatic pressing (HIP) and BST + OA. It was demonstrated that the three PTs led to the decomposition of α’ martensite inherited from the LPBF process and the formation of variable α + β structures. The SR + BA treatment forms a basket weave structure having an average α lamellae width of ~3 µm and surrounded by ~1 µm-sized zones of segregated β phase (4.6–5.2% β phase content) and globalized α phase (~10 µm in size) inside prior columnar β grains (~100 µm in width). The SR + BST + OA treatment forms semi-equiaxed α grains (~300 µm) containing colonies (~50 µm) of parallel-oriented α plates (~6 µm), and β phase (5.8–7.5%) in the interplate spacing. The HIP + BST + OA treatment leads to the formation of large grains (~500 µm) with both basket weave and colony (~40 µm) α structures containing α plates (1.1–4.2 µm) and β phase (5–7.1%). To compare the impact of these PTs on the mechanical properties of LPBF components, they were subjected to static and fatigue tensile testing at room temperature. The best combination of mechanical properties (yield strength ~920 MPa, ultimate strength ~1000 MPa, elongation to break ~22.5%, and fatigue strength ~600 MPa, 107 cycles) was obtained in the case of SR + BA specimens. These results demonstrate that an adequate thermal treatment, such as SR + BA, of the LPBF Ti64 components, could be a valuable and less expensive alternative to the established HIP + BST + OA treatment procedure when fatigue life is the main concern.

Mechanical Characteristics Evaluation of a Single Ply and Multi-Ply Carbon Fiber-Reinforced Plastic Subjected to Tensile and Bending Loads.

Carbon fiber-reinforced composites represent a broadly utilized class of materials in aeronautical applications, due to their high-performance capability. The studied CFRP is manufactured from a 3K carbon biaxial fabric 0°/90° with high tensile resistance, reinforced with high-performance thermoset molding epoxy vinyl ester resin. The macroscale experimental characterization has constituted the subject of various studies, with the scope of assessing overall structural performance. This study, on the other hand, aims at evaluating the mesoscopic mechanical behavior of a single-ply CFRP, by utilizing tensile test specimens with an average experimental study area of only 3 cm2. The single-ply tensile testing was accomplished using a small scale custom-made uniaxial testing device, powered by a stepper motor, with measurements recorded by two 5-megapixel cameras of the DIC Q400 system, mounted on a Leica M125 digital stereo microscope. The single-ply testing results illustrated the orthotropic nature of the CFRP and turned out to be in close correlation with the multi-ply CFRP tensile and bending tests, resulting in a comprehensive material characterization. The results obtained for the multi-ply tensile and flexural characteristics are adequate in terms of CFRP expectations, having a satisfactory precision. The results have been evaluated using a broad experimental approach, consisting of the Dantec Q400 standard digital image correlation system, facilitating the determination of Poisson’s ratio, correlated with the measurements obtained from the INSTRON 8801 servo hydraulic testing system’s load cell, for a segment of the tensile and flexural characteristics determination. Finite element analyses were realized to reproduce the tensile and flexural test conditions, based on the experimentally determined stress–strain evolution of the material. The FEA results match very well with the experimental results, and thus will constitute the basis for further FEA analyses of aeronautic structures.

Specifics of diagnostics and investigation of material properties in pipes with planar defects

The paper presents findings of a study on planar defects formed on the inner surface of gas pipeline metal in the operation process. The diagnostic indicators of a defective section were determined and analyzed using the intelligent pigging data. A broad range of research was carried out, including visual and measuring control of the object, step-by-step ultrasonic thickness measurement, chemical analysis, optical and electron microscopy, microhardness measurement of defective and defect-free areas, static tensile and impact bending tests. The structure and morphology of defective and defect-free areas were considered. It was determined that the cause of the defects is contamination of the source material with gas pores and fluorspar residues. The defects of planar nature are formed during rolling and can be characterized as metal delamination. The maximum detected thickness of the inclusions was 1.0 mm, however, the main part was rolled to 10.0 μm. The key feature of defects is their location on various levels throughout the wall cross-sections, ranging from one to four detected layers or groups of rolled discontinuities. It is shown that such defects lead to a change in the strength properties of defective area, uneven distribution of loads and reduction in safety margin of the object.

Self-sensing performance of cement-based sensor with carbon black and polypropylene fibre subjected to different loading conditions

Different dosages of carbon black (CB) were used to manufacture the cost-effective and highly sensitive polypropylene (PP) fibre cement-based sensors in this paper. The distribution of conductive phases and static electrical resistivity were firstly investigated through microscopic characterization and static resistivity, respectively. Then the self-sensing performance of the CB/PP fibre cementitious composites in response to different loading conditions was comprehensively assessed by cyclic compression, notched bending, and splitting tensile conditions. The results indicate that the improvement of PP fibres on conductivity and self-sensing performance is heavily dependent on the coating efficiency of CB nanoparticles on the surfaces of PP fibres. In particular, the cement-based sensors with excellent CB coating efficiency demonstrate the most promising pre-crack flexural sensing capacity. Additionally, the strain hardening characteristics and damage sensing ability for the intrinsic cement-based sensors were explored by splitting tension together with digital image correlation tracking. Apart from a strong linear correlation between fractional change of resistivity and tensile strain during the strain hardening stage, the distinct sensing characteristics between the strain hardening stage and softening stage can give the diagnosis of damage stage (strain hardening stage or softening stage) and crack width (microcracking or macrocracking). Therefore, the intrinsic CB/PP fibre cementitious composites as robust cement-based sensors can provide a great potential to sense strain and deformation as well as detect crack and damage for concrete infrastructure subjected to various loading conditions.

High elastic modulus polyethylene – A two-stage multi-axial rolling and orientation process

In this study, we propose a novel two-stage solid-state processing technique to fabricate thin-oriented high-density polyethylene (HDPE) rods with enhanced mechanical properties. This unique solvent-free technology involves biaxial rolling (Stage 1) followed by a uniaxial orientation procedure (Stage 2). The oriented thin HDPE rods exhibit an impressive modulus of 37 GPa. This is a result of a complex, oriented composite structure containing crazes with a network of interlocking fibers. Surprisingly, the high-modulus thin rods were created under relative low uniaxial tensile orientation conditions having draw ratio of eleven. Gel-spun ultra-high-molecular-weight fiber processing requires orientations greater than thirty. A corresponding scaled hierarchical model was proposed to summarize the process-structure-property relationships. This study demonstrates a strategy for creating high-modulus polymeric materials via controlled solid-state processing.

The effect of Nb on the hydrogen embrittlement susceptibility of Q&P steel under static and dynamic loading

In the present study, the effect of Niobium (Nb) on the hydrogen embrittlement resistance of Quenched and Partitioning (Q&P) steel is investigated. For this purpose, the hydrogen uptake level and its impact on the mechanical properties of a Nb-free and a 0.024 wt% Nb Q&P steel are thoroughly analysed. The hydrogen trapping capacity is evaluated via thermal desorption spectroscopy (TDS). In-depth analysis of the desorption kinetics at different heating rates allows identification and quantification of the available trapping sites. The hydrogen embrittlement sensitivity of both steels is characterized using static and dynamic tensile tests. The addition of Nb results in an increase of the hydrogen concentration by more than 25%. The larger hydrogen content in the Nb steel, as a result of the higher fraction of grain boundaries/interphases, gives rise to a more severe embrittlement of the Nb steel compared to the Nb-free one. In addition to the larger hydrogen fraction in the Nb Q&P steel, the larger retained austenite fraction of low stability is detrimental due to the larger fraction of high carbon martensite formed when straining. This results in higher susceptibility to hydrogen embrittlement of the Nb microalloyed steel due to the brittle character of the high carbon martensite that forms easily during straining. Under dynamic loading conditions, the hydrogen embrittlement of both steels is minimal, which is attributed to a reduced hydrogen diffusion and the suppression of the transformation induced plasticity (TRIP) effect due to adiabatic heating.

Particleboards manufactured from Tectona grandis wood waste with homogeneous and three-layer heterogeneous compositions for commercial purposes

Tectona grandis wood presents decent dimensional stability as well as highly suitable physical and mechanical properties. These characteristics have encouraged the intense usage of this species, which also includes the reuse of wood processing waste for panel production. Using teak wood waste, this study aims to manufacture and evaluate heat-pressed particleboards at 5 MPa and 100 °C, by being glued with castor oil-based polyurethane resin at proportions of 10% for the homogeneous boards and 12% for the heterogeneous solutions. Single-layer (homogeneous) boards were compared with three-layer particleboard specimens (heterogeneous) having the finer particles in the outer layers. The basic density, moisture content, modulus of rupture and modulus of elasticity in the static bending and perpendicular tensile, water absorption, and thickness swelling after 24 h were evaluated to support this comparative study. All the manufactured particleboards met the standardized requirements of performance, thus being very feasible for usage as non-structural boards. When the two different compositions were analyzed, a considerably better performance of the three-layered particleboards was identified when compared to the homogeneous panels.

Numerical study on mechanical erosion behaviour of the burning-free Al2O3–C bottom nozzle during casting

The burning-free bottom nozzle is a novel component for accurately controlling the molten steel flow during the casting steel process. The effect of the thermal mechanical behaviour of burning-free Al2O3–C bottom nozzle materials under extreme temperatures during casting on the thermally induced failure was investigated. First, the high-temperature dynamic Young's modulus and thermal expansion of the bottom nozzle materials were tested in the temperature range of 300–1473 K. A composite material constitutive model, a thermal conductive model and the concrete damage plasticity model (CDP) were adopted to examine the mechanical erosion behaviour of the Al2O3–C bottom nozzle in the casting process based on Finite Element Method (FEM). Results shown that the area near the core of the bottom nozzle was at a high temperature and under tensile stress conditions, whereas the edge area restricted by the external steel shell was mainly under compressive stress conditions. Then, the cracking tendency was evaluated, and an optimised bottom nozzle with a composite structure was proposed. The burning-free Al2O3–C bottom nozzle with a composite structure has an advantage in reducing the risks of cracking and extending the service life compared with the nozzle made of homogeneous materials. This work can make a significant contribution to the design of high performance bottom nozzles.

Experimental study on bond performance at UHPC-UHPC cold joints

There has been a rapid increase in the use of ultra-high-performance concrete (UHPC) as a construction or repair material worldwide due to its superior mechanical and durability characteristics. However, the bond strength of UHPC cast at different times is inadequately understood. This study examined the bond performance at UHPC-UHPC interfaces using five different surface preparations with mean texture depths (MTDs) ranging from 0.43 mm to 6.38 mm. The effect of fiber exposure techniques such as pressure washing, sandblasting, and needle scaler treatment on the bond performance at UHPC-UHPC cold joints was considered. The study also included the effect of grooved and smooth surface preparations on bond strength. The bond strength was investigated under tensile, shear and compression-shear stress conditions. The influence of inclination angle of the interface with different shear to compression ratios was studied. The results indicate that the presence of steel fibers at the interface plays a significant role in bond capacity by enhancing the bond strength and providing more interlock that results in ductility. The majority of the failure modes were at the bond interface due to the superior mechanical properties of UHPC. The cohesion and friction coefficients were determined from the experimental data and compared with values from design codes. It was discovered that pressure washed and grooved surface preparations exhibited superior bond performance compared to the other surface preparations under the stress conditions considered in this study.

Ultrasonic-based tensile force estimation for cylindrical rod at various temperature conditions

This study presents the development of a tensile force estimation technique based on the ultrasonic bulk wave for cylindrical rod in a suspension bridge anchor system. Three piezoelectric macro fiber composites (MFC) transducers are installed on the surface of a cylindrical rod specimen for the generation and sensing of ultrasonic bulk waves. Ultrasonic responses are obtained at various tensile force levels and temperature conditions, and the relationship between the time lag of the ultrasonic response and the tensile force is established. In particular, the temperature effect on the tensile force estimation is theoretically derived and compensated for field applications. The originality of this study includes (1) theoretical derivation and investigation of the relationship between an applied tensile force level and the time lag of an ultrasonic response considering the variations of temperature, density, and elastic modulus, (2) development of a tensile force estimation and temperature compensation technique without temperature measurement, and (3) application to the tensile force estimation of the rod structure commonly used in a suspension bridge anchor system. The performance of the developed tensile force estimation technique was examined based on mock-up experiments of the rod structure of a real suspension bridge anchor system.

Self‐Powered Smart Shoes with Functional Ribbon Units for Monitoring Human Gait

AbstractThis study presents novel, self‐powered smart shoes that can detect various gait patterns and harvest electrical energy. A functional ribbon unit made of polyvinylidene fluoride (PVDF) ribbon and conductive fabric tape is used for the energy harvester, and a dynamic sensor is used for monitoring the gait patterns. To determine the optimal number of ribbon units and effective elongation levels for energy harvesting, static tensile and repetitive electromechanical tests are performed. In addition, the generated output voltage and energy storage capacity according to the ribbon configuration are experimentally investigated. To enhance the energy‐harvesting efficiency of the functional ribbon unit, a high‐stiffness lightweight carbon composite frame is installed at the heel part inside the smart shoes, and three ribbon units are fastened to it. From the performance test, it is concluded that the harvester generates sufficient electric power, which is stored in successive capacitors; subsequently, the generated electric power is stored in a lithium‐ion battery. Moreover, various gait patterns are successfully identified, and gait speed is estimated using the proposed smart shoes.

Influence of alternative rice husk ash filler on bitumen emulsion-based recycled asphalt

The influence of rice husk ash (RHA) as an alternative active filler on the mechanical properties of bitumen emulsion-based recycled asphalt specimens in high- and low-temperature domains was investigated. The experimental methodology was comprised of static indirect tensile and wheel-tracking testing, as well as scanning electron microscopy using secondary electrons and energy dispersive X-ray spectroscopy. The results showed that the increase in the mass fraction of RHA gradually improved the water sensitivity and the high-temperature performance of specimens, but also negatively affected their low-temperature performance. The mass fraction of RHA above 1.5%, resulted in a tensile strength ratio after freeze–thaw and immersion of more than 80%, and in the dynamic stability in rutting test above 4500 mm−1, but also the low-temperature indirect tensile strength below 2.0 MPa. Considering the relevant regulations, the mass fraction of RHA should be in the range of 1–1.5%.

Experimental and numerical investigations on monotonic tensile behavior of grouted sleeve couplers with different splicing configurations

This study presents experimental and numerical investigations on the tensile behavior of grouted sleeve (GS) couplers splicing steel bars with transition splicing and different strength grades intended for use in shifted plastic hinge applications. Sixteen GS specimens, with testing parameters that included GS coupler size, steel bar diameter, and transition splicing index, were assembled and tested under static monotonic tensile tests. Also, one-dimensional finite element (FE) modeling was conducted to establish the bond–slip constitutive models, which govern the bar–grout interfaces at different regions of the GS coupler, by inverse analysis.Experimental results showed consistent failure mode, which was bar rupture away from the coupler region, for all splicing configurations of GS couplers, which demonstrated the ability of GS couplers to fully develop the ultimate stress in the spliced bars. Results also revealed an approximately piecewise linear relationship that governs the ratio between the strain within the coupler region and strain in the spliced normal strength steel bar, in which the strain ratio decreases with larger sleeve sizes and higher transition indices. Furthermore, results showed that GS couplers exhibited considerable slip that increased with bar size and can be of benefit to GS precast members that are subjected to significant rotation demands. The proposed bond–slip models for GS couplers were simple but accurate in slip prediction and they can be very helpful in the analytical modeling of precast members containing GS couplers.

Effect of Diluents on Mechanical Characteristics of Epoxy Compounds.

The aim of this work is to assess the influence of different commercial diluents on some mechanical properties of two bisphenolic epoxy compounds, cold-cured by a polyamide curing agent, to be employed as epoxy structural adhesives for building and industrial applications. The diluents under analysis were epoxy, bituminous, nitro, acrylic and extraction. The choice of these products was made on the basis of their wide commercial availability as diluents for epoxies used as adhesives and in different industrial and construction applications. The diluents were all added in small proportions, i.e., from 1 to 10 g per 100 g of epoxy resin. The cold-cured epoxy compounds were subjected to compressive (according to ISO 604) and static tensile (according to ISO 527-1) tests. The same mechanical tests were performed on both unmodified epoxy resins, for comparison purposes. On the basis of the obtained results, it was concluded that the influence of the presence of a diluent, and of its amount, on the mechanical properties of epoxy compounds depends on the type of resin and of diluent, as well as on the mechanical characteristics analyzed.

Carbon Fiber/PLA Recycled Composite.

Due exceptional properties such as its high-temperature resistance, mechanical characteristics, and relatively lower price, the demand for carbon fiber has been increasing over the past years. The widespread use of carbon-fiber-reinforced polymers or plastics (CFRP) has attracted many industries. However, on the other hand, the increasing demand for carbon fibers has created a waste recycling problem that must be overcome. In this context, increasing plastic waste from the new 3D printing technology has been increased, contributing to a greater need for recycling efforts. This research aims to produce a recycled composite made from different carbon fiber leftover resources to reinforce the increasing waste of Polylactic acid (PLA) as a promising solution to the growing demand for both materials. Two types of leftover carbon fiber waste from domestic industries are handled: carbon fiber waste (CF) and carbon fiber-reinforced composite (CFRP). Two strategies are adopted to produce the recycled composite material, mixing PLA waste with CF one time and with CFRP the second time. The recycled composites are tested under tensile test conditions to investigate the impact of the waste carbon reinforcement on PLA properties. Additionally, thermogravimetric analysis (TGA), X-ray diffraction (XRD), and Fourier-transformed infrared spectroscopy (FTIR) is carried out on composites to study their thermal properties.

Effect of steel fiber type and content on the dynamic tensile properties of ultra-high performance cementitious composites (UHPCC)

As one of the most promising construction and building materials in the past 30 years, ultra-high performance concrete (UHPC) has attracted a great deal of attention and the studies on its improvement and dynamic tensile behaviors become more important for its wider use in the related fields. In this contribution, a novel ultra-high performance cementitious composites (UHPCC) was developed with lower cement content, 20% of cement is replaced with fly ash and blast furnace slag, to reduce the raw material cost and carbon emission in production. Uniaxial compression, quasi-static and dynamic splitting tests were carried out to investigate the influences of steel fiber type (straight fiber and waved fiber) and content (volume fraction (0%, 1%, 2%)) on the uniaxial compressive strength, static tensile strength and dynamic tensile behaviors for current UHPCC material. The dynamic splitting tests were conducted on 100 disc specimens (75 mm in diameter and 37.5 mm in thickness) under five different impact pressure at a strain-rate range of 20–110 s−1 to study the strain rate effect by using a Split Hopkinson pressure bar (SHPB) system and the samples’ failure processes were captured by a high-speed camera. Based on the test results, the variations of energy absorption with the fiber type and content under static and dynamic tensile conditions are also analyzed, and combined with the experimental data from previous studies, an improved empirical tensile strength rate sensitivity (DIFft) model is proposed, which agrees well with the experiment results and can be used in the numerical simulation. At last, the failure process and pattern of different types of UHPCCs in the dynamic splitting test are also studied.

The effect of crystal region on the shape memory in polylactic acid matrix

The paper analyzed the effect of tensile conditions on the shape memory effect of PLA plates. The experimental results showed that the PLA plates presented excellent recovery ratio and recovery stress at lower stretch temperatures. In shape memory system of PLA, the crystal regions acted as network points significantly influenced the shape memory effect. The change of crystal structure of PLA plates at different strecthing conditions was investigated. The structural evolution model of lamallae during the stretching process were established.

The Influence of Fly Ash on the Mechanical Properties of Water Immersed All Waste Composites.

The paper presents new value-added composite materials prepared by recycling tire rubber, polyethene terephthalate (PET), high-density polyethene (HDPE), wood sawdust, and fly ash. The composites were manufactured through the compression molding technique for three temperatures (150 °C, 160 °C, and 190 °C) previously optimized. The addition of fly ash as reinforcement in polymer blends is a viable route to improve the composite” properties. The paper aims to assess the effect of fly ash on the mechanical properties and water stability of the new all waste composites considering their applications as outdoor products. The static tensile (stress-strain behavior) and compression properties of the composites were tested. The fly ash composites were characterized in terms of wetting behavior and surface energies (contact angle measurements); chemical structure of the new interface developed between composite” components (FTIR analysis), crystalline structure (XRD analysis), surface morphology and topography (SEM, AFM). The addition of fly ash promoted the development of the hybrid interfaces in the new composites, as FTIR analysis has shown, which, in turn, greatly improved the mechanical and water resistance. The novel all waste composites exhibited lower surface energies, larger contact angles, and smoother morphologies when compared to those with no fly ash. Overall, the study results have revealed that fly ash has improved the mechanical strength and water stability of the composites through the formation of strong hybrid interfaces. The study results show optimal water stability and tensile strength for 0.5% fly ash composites cured at 190 °C and optimal compressive strength with good water stability for 1% fly ash composite cured at 150 °C.

Assessing the Effect of Fe3O4 Nanoparticles on the Thermomechanical Performance of Different Forms of Carbon Allotropes/Epoxy Hybrid Nanocomposites

The incorporation of ceramic nanoinclusions in carbon nanocomposites can induce additional functionality in the field of magnetic properties, piezoelectricity, etc. In this study, series of nanocomposites, consisting of different carbon nanoinclusions (carbon black, MWCNTs, graphene nanoplatelets, nanodiamonds) and magnetite nanoparticles incorporated into a commercially available epoxy resin were developed varying the filler type and concentration. Experimental data from the static tensile tests and dynamic mechanical analysis (DMA) demonstrated that the elastic tensile modulus and storage modulus of hybrid nanocomposites increase with an increase in filler content up to almost 100% due to the inherent filler properties and the strong interactions at the interface between the epoxy matrix and the nanoinclusions. Strong interactions are implied by the increasing values of the glass transition temperature recorded by differential scanning calorimetry (DSC). On the contrary, tensile strength and fracture strain of the nanocomposites were found to decrease with filler content. The results highlight the potentials and capabilities of developing hybrid multifunctional nanocomposites with enriched properties while holding their structural integrity.