Ductile Specimens Research Articles

Bond-Based Peridynamic Model for Tensile Deformation and Fracture of Polycarbonate and Polypropylene

Fracture mechanics has been a crucial aspect in the field of engineering science as technologies are rapidly growing nowadays. Various numerical methods have been developed to analyze fracture behaviour in different types of materials used in industries. Meanwhile, the application of polymers garners attention worldwide due to outstanding characteristics such as good strength, lightweight, and high temperature resistance, exemplified by polymers like polycarbonate (PC) and polypropylene (PP). Hence, failure aspects of such materials must be taken into consideration when conditions arise that may lead to failure, such as high-load impact, fatigue, and extreme temperatures. In this study, a bond-based Peridynamic model (PD) for the tensile behaviour, including fracture, of polymers has been developed. The PD model is constructed using the Centos software and encompasses both brittle and ductile fracture behaviours. Numerical results, including crack propagation, damage zone, and force-extension curves of notched specimens, are validated by comparison with experimental results of PC and PP. Through the validation process, PC specimens exhibit a difference percentage range for maximum load and rupture extension of 2.9% to 18.8% and 2.4% to 4.6%, respectively. PP specimens show a difference percentage range for maximum load and rupture extension of 31.2% to 43.5% and 0.9% to 30%, respectively. Consequently, the validation results indicate that the PD model for brittle specimens aligns more closely with experimental data compared to the PD model for ductile specimens.

Dimensional Accuracy and Mechanical Characterization of Inconel 625 Components in Atomic Diffusion Additive Manufacturing

Metal material additive manufacturing (MEAM) has risen in interest in the last five years as an alternative to powder bed processes. MEAM is promising for generating shelled components with defined infill structures, making it very interesting for lightweight engineering. Atomic Diffusion Additive Manufacturing (ADAM) is a filament-based MEAM process patented by Markforged Inc. that provides a closed process chain from preprocessing to the final sintering of printed green parts. This study focuses on Inconel 625, which is of high interest in the aerospace industry, and assesses its dimensional accuracy and tensile properties regarding different print orientations and solid, triangular, and gyroid infill structures. The results showed that neither the dimensional accuracy nor the sintering shrinkage was significantly influenced by the printing orientation or the infill structure. In the context of lightweight engineering, the infill structures proved beneficial, especially within the elastic region. Generally, triangular infill patterns resulted in higher stiffness, while gyroids led to more ductile specimens. A mass-related evaluation of tensile testing elucidates that with the aid of the infill structures, weight savings of 40% resulted in mechanical performance decreasing by only 20% on average, proving its high potential for lightweight design.

A Direct Impact Tension Bar setup for testing low-impedance materials at intermediate rates of strain

This study introduces a Hopkinson bar variation, well-suited for probing low-impedance materials in the intermediate strain-rate regime. Currently, servo-hydraulic machines (SHM) and drop weight towers are considered primary for measuring mechanical properties at strain-rates 101 to 102/s. However, such setups often exhibit detrimental oscillations due to inertial response. These oscillations can be severe, rendering recorded data unreliable for inferring strain-rate effects. Our Direct Impact Tension Bar (DITB) offers accurate force signals devoid of ringing artefacts. The setup has a long 16 ms pulse duration, facilitating intermediate strain-rate tensile tests on extended ductile specimens. We discuss the DITB construction breakdown and demonstrate its applicability through dynamic tensile tests on sheet-type polycarbonate (PC) specimens at 150/s, compared to servo-hydraulic data. DITB results yield high-quality data, free from oscillations.

Behavior of corrosion damaged non-seismically and seismically detailed reinforced concrete beam-column sub-assemblages under cyclic loading

Corrosion of reinforcement requires immediate redressal as it poses a severe threat to the serviceability and seismic performance of the existing reinforced concrete structure. Taking this into consideration, the current study presents an experimental assessment of the seismic behavior of corroded exterior beam-column joint sub-assemblage under quasi-static reverse-cyclic loading. A total of eight exterior beam-column joint specimens i.e., four having traditional non-ductile transverse reinforcement detailing as per IS 456:2000 and the remaining specimens ductile detailed according to IS 13920:2016 were cast. One specimen from each detailing regime was tested uncorroded and acted as a control specimen while the remaining six specimens were subjected to varying levels of accelerated corrosion. The experimental results illustrated that the sliding phenomenon in the hysteresis curve gradually increases and a drastic fall in energy dissipation, stiffness, and post-yield displacement were seen as the corrosion progresses within reinforcing bars. The failure mode shifted from diagonal joint shear failure observed in control specimens to longitudinal and major flexural cracking failure along the beam reinforcement. First-level corroded specimens showed a slightly increased ductility factor, indicating that low levels of corrosion may improve ductility. However, after 10% corrosion, all corroded specimens showed poor seismic performance and the cumulative energy dissipation curve tends to go flat at approximately half the displacement as compared to control specimens. The cumulative energy dissipation of non-ductile and ductile specimens damaged to the most severe level of corrosion in this study was only 0.3 and 0.4 times that of respective control specimens. In general, the ductile detailed specimens showed better seismic performance than the corresponding non-ductile detailed specimens owing to the closer arrangement of stirrups.

Analysis of the ductility of reinforcement structural steel rods from some local mini mills in Nigeria using theoretical and statistical approach

Analysis of the ductility of reinforcement structural steel rods from some local mini mills in Nigeria using theoretical and statistical approach has been carried out. Ductility is one parameter required of reinforcement structural steels; it prevents sudden failure of reinforced concrete structures. In this work samples were collected from four different mini mills and subjected to tensile test. The initial gauge value of the test specimens was noted. The failed test specimens were then joined together individually to measure the final length at failure and to calculate the % elongation at failure. Stress –strain plots were made to determine the pattern of deformation and failure. The results show that all the specimens have stress-strain curves typical of ductile materials. The % elongation at failure of specimen 3 was the highest at 15.37, the other specimens too all had reasonable % elongation; meaning they are ductile materials. The statistical approach used in the analysis of the work produced results that completely agreed with the theoretical analysis of the work. The statistical analysis used included the use of expected values calculation to select the best ductile specimen, the use of bar chart to show the specimen with the highest % elongation and the one with the lowest value of % elongation, the use of to test if all the specimens have the same % elongation or ductility, and the use of spearman rank correlation coefficient to test if the % elongation is associated with the maximum loading of the specimens. In conclusion the work has highlighted the need for structural reinforcement steel bars to have reasonable ductility in order to avoid sudden failures associated with brittle materials, when used in buildings and other concrete structures.

Machinability of alloy ductile iron and forged 16MnCr5 steel

Abstract The remarkable mechanical properties of austempered ductile iron (ADI) render ADI as an alternative material for forged steels. On the other hand, the high strength and hardness make the machining of ADI to be challenging. In this study, the ADI is presented as an alternative material to fabricate the ring gear of the two-wheel tractors. A series of experiments were designed to evaluate the machinability of the alloyed ductile iron before the austempering process. 16MnCr5 alloy steel and alloyed ductile specimens were subjected to drilling tests. The effect of drilling parameters on thrust force was investigated based on a design of experiments approach. A regression model was established to predict thrust force at various drilling conditions. Then, the machinability rating was defined as the ratio of the predicted thrust forces. The results showed that at lower feed rates, the thrust force is very close for both materials, such that the estimated machinability rating is 86%.

Influence of Shot-Peening on Wear Resistance of Austempered and Quench-Tempered Ductile Irons

In this research, ball-on-plate reciprocating sliding wear tests were conducted on shot-peened specimens of ductile iron heat treated by either austempering or quench-tempering. Hardness and microstructure were evaluated to understand the phase transformation, and X-ray diffraction was used to measure the residual stress. It was found that feather-like ausferrite was formed when using high austempering temperatures. In sliding wear tests, austempered ductile iron specimens had better wear resistance than quench-tempered ductile iron specimens before and after receiving shot-peening. Crack and adhesive wear were the two main wear mechanisms on ductile iron specimens. The shot-peening resulted in the increase of residual compressive stress and surface hardness, which could retard the nucleation and propagation of cracks and reduce the amount and size of smeared areas.

Evaluation of machinability of alloy ductile iron in term of thrust drilling force

The main aim of this work is the assessment of the machinability of alloyed ductile iron before the austempering process. 16MnCr5 alloy steel and alloyed ductile specimens were subjected to drilling tests. The effect of drilling parameters on cutting force was investigated based on the Taguchi approach. Based on the results, a regression model was established to predict thrust force at various drilling conditions. The predicted thrust forces ratio was then used to evaluate the machinability of alloyed ductile respect to the 16MnCr5 alloy steel. The results showed that at lower feed rate, the normal drilling force is very close for both materials, such that the estimated machinability rating is 86%.

A parametric investigation on friction stir welding of Al-Li 2099

ABSTRACT Aluminum-lithium alloys have lower density compared to other traditional aluminum alloys and as such, are being used in lightweighting applications. However, while the microstructure and mechanical behavior of the wrought form of aluminum-lithium alloy 2099 are well characterized, the effect of process variability in friction stir welding (FSW) of this alloy is not well understood. As such, a parametric investigation was performed to examine the effects of tool rotational rates and transverse speeds during FSW on the corresponding microstructure and tensile strength of aluminum-lithium alloy 2099. In general, a strong correlation between tool translation speed and tensile strength and ductility was found. Specifically, the elongation to failure and ultimate tensile strength increased as the transverse speeds increased due to a direct decrease in the heat input. However, elongation to failure and ultimate tensile strength were less dependent on the rotational rate since adequate material mixing was achieved and strain rate sensitivity is negligible at these strain rates. Postmortem analysis revealed a greater presence of micro void and coalescence on the fracture surface for the more ductile specimens as opposed to a higher occurrence cleavage fracture due to the coarsening of intermetallics.

Density functional calculations of elastic and thermal properties of zinc-blende HgSxSe1−x, HgSxTe1−x and HgSexTe1−x ternary alloys

Elastic and thermal properties of zinc-blende HgSxSe1−x, HgSxTe1−x and HgSexTe1−x ternary specimens are calculated with density functional FP-LAPW approach. Elastic constants increases, but elastic compliances decreases nonlinearly with enhancement in dopant chalcogen concentration in each system. Each of the highly ductile specimens shows mechanical and dynamical stability, elastic anisotropy, reasonably compressibility against elastic deformation, plasticity and central nature of interatomic bonding forces. Hardness of compounds in any system enhances with enhancement in dopant chalcogen composition. Mixed kind of bonding with dominancy of ionic bonding and bond bending over stretching are found in each specimen. Covalency of specimens decreases, while Philip ionicity increases with enhancement in dopant chalcogen concentration in each system. The HgS, possessing maximum Debye temperature, is the stiffest among all the compounds. In each system, calculated Debye temperature, Debye frequency, Gruneisen parameter, minimum thermal conductivity and melting temperature of specimens increases nonlinearly with enhancement in dopant chalcogen concentration.

Novel steel bracket and haunch hybrid system for post-earthquake retrofit of damaged exterior beam-column sub-assemblages

In the present study, an innovative steel bracket and haunch hybrid scheme is devised, for retrofitting of earthquake damaged deficient beam-column sub-assemblages. Formulations are presented for evaluating haunch force factor under combined load case of lateral and gravity loads for the design of double haunch retrofit. The strength hierarchies of control and retrofitted beam-column sub-assemblages are established to showcase the efficacy of the retrofit in reversing the undesirable strength hierarchy. Further, the efficacy of the proposed retrofit scheme is demonstrated through experimental investigations carried out on gravity load designed (GLD), non-ductile and ductile detailed beam-column sub-assemblages which were damaged under reverse cyclic loading. The maximum load carried by repaired and retrofitted GLD specimen in positive and negative cycle is 12% and 28% respectively higher than that of the control GLD specimen. Further, the retrofitted GLD specimen sustained load up to drift ratio of 5.88% compared with 2.94% drift sustained by control GLD specimen. Repaired and retrofitted non-ductile specimen, could attain the displacement ductility of three during positive cycle of loading and showed improved ductility well above the expected displacement ductility of three during negative cycle. The hybrid haunch retrofit restored the load carrying capacity of damaged ductile specimen to the original level of control specimen and improved the ductility closer to the expected displacement ductility of five. The total cumulative energy dissipated by repaired and retrofitted GLD, non-ductile and ductile specimens are respectively 6.5 times, 2.31 times, 1.21 times that of the corresponding undamaged control specimens. Further, the damage indices of the repaired and retrofitted specimens are found to be lower than that of the corresponding control specimens. The novel and innovative steel bracket and haunch hybrid retrofit scheme proposed in the present study demonstrated its effectiveness by attaining the required displacement ductility and load carrying capacity and would be an excellent candidate for post-earthquake retrofit of damaged existing RC structures designed according to different design evolutions.

Yield Stress and Reversible Strain in Titanium Nickelide Alloys after Warm Abc Pressing.

The results of the position analysis of the yield stress τ0.3 on the "stress–strain" (τ–γ) dependences, received at the torsion of specimens of Ti49.8Ni50.2 (at%) alloy are presented. The critical stress τ0.3 (IV), corresponding to the end of linear stage III and the beginning of the intensive development of plastic strain at stage IV, preceding the fracture of the specimens, were obtained as well. The structure of the specimens was transformed from coarse-grained to microcrystalline as a result of warm (723 K) abc pressing with a true deformation e of 8.4. The regularities of the development of reversible inelastic strain (superelasticity, SE, and shape memory effect, SME) and plastic strain γpl after isothermal (295 K) loading of specimens up to τ ≤ τ0.3(IV), unloading, and their subsequent heating up to 500 K are studied. From the joint analysis of the “τ–γ” dependences obtained at 295 K and "plastic strain–total strain" dependences the yield stress τ0.3 corresponding to the development of 0.3% of the plastic strain under loading of the specimens was determined. Critical stress τ0.3(IV) was determined as equal to the stress corresponding to a deviation of 0.3% from the linear “τ–γ”dependence at stage III. It is shown that the yield stress τ0.3 for all specimens is localized at the beginning of stage III for all specimens. The ratio τ0.3(IV)/τ0.3 is from 2.3 to 3.8. The accumulation of plastic strain at stage III (after loading with τ from τ0.3 to τ0.3(IV)) is from 2.4% to 4.7% (depending on the true deformation of the specimens during warm abc pressing). Thus, stage III is the stage of deformation hardening of specimens under torsion. On the basis of the results of this and previous works it is shown that, in alloys with thermoelastic martensitic transformations and with thermomechanical memory, the ratio τ0.3(IV)/τ0.3 can vary in a wide range: in reinforced specimens τ0.3 can be close to τ0.3(IV), and in more ductile specimens τ0.3 can be significantly less than τ0.3(IV). However, in order to correctly determine the yield stress of τ0.3 and the corresponding strain γt(0.3), it is necessary to carry out a joint analysis of “τ–γ” and "plastic strain–total strain" dependencies.

Nonseismic and seismic designed beam-column joints with rebar end anchors – Behaviour under reverse cyclic loading

ABSTRACT In the present study, performance of the reinforced concrete beam column joints with two design criteria, i.e., gravity load design and ductile design is evaluated. Effect of detailing with bent reinforcement and with end anchors in joint region is studied using full scale experiments under reverse cyclic loading. The crack formation, load–displacement hysteresis behavior, energy dissipation, strength and stiffness degradation, etc. are studied. The plastic zone formation in beam region of the end anchor specimen is much wider and prominent than the bent reinforcement specimens. Both the ductile specimens provide almost same shear deformation and energy dissipation.

Mixed mode I/II failure prediction of thin U-notched ductile steel plates with significant strain-hardening and large strain-to-failure: The Fictitious Material Concept

In wide range of ductile materials, the strain-to-failure and the strain-hardening are simultaneously significant, for which, there is no valid K-based fracture toughness (KIc or Kc) based on the standard test methods. So, prediction of the load-carrying capacity (LCC) of notched specimens made of these materials by means of the Equivalent Material Concept (EMC) is impossible. On the other hand, because of large value of the predicted failure load resulted from the large strain-to-failure, the modified EMC (MEMC) seems inefficient in LCC prediction of notched members. Consequently, for such ductile materials, both EMC and MEMC are null. The Fictitious Material Concept (FMC) is proposed in the present study to overcome this major limitation, by which fictitious values of Young's modulus and fracture toughness are defined and calculated for the real ductile material to predict LCC of notched ductile specimens. For this aim, first, U-notched specimens made of SUS 316 stainless steel with good ductility, large strain-to-failure, high elastic modulus, and significant strain-hardening, are evaluated for fracture under pure mode I and mixed mode I/II loadings both experimentally and theoretically. The U-notched specimens with different notch tip radii and notch inclination angles are produced and tested, and their failure loads are experimentally recorded. Then, the test results are theoretically predicted by linking FMC to the maximum tangential stress (MTS) and mean stress (MS) brittle fracture criteria with no need for time-consuming and complex elastic-plastic analyses. A good agreement is observed between the predictions of both FMC-MTS and FMC-MS combined criteria and the experimental results. Meanwhile, the experimental observations as well as the results of elastic-plastic finite element analysis confirm that all of the specimens tested fail by the gross-yielding (GY) regime.

Failure of P-surfaced Shellular subjected to internal pressure

This work measured the internal pressure strengths of a periodic shell architecture, named Shellular, made of Ni-P, Cu, and silica. For this purpose, a simple and effective test method was applied. The results were analyzed using elementary mechanics and finite element analyses. The critical pressures of the most ductile Shellular specimens, made of Cu, were the highest among them, despite the low strength of Cu. Although the specimens had substantial geometrical imperfections and were made of thin shells of a micrometer, the strengths of Cu Shellulars under internal pressure were comparable to that of a conventional cylindrical pressure vessel.

Finite Element Analysis of an Aluminum Alloy Using Progressive Failure Algorithm

This study aims to develop a reliable finite element analysis procedure to model the complete fracture of ductile specimens using the progressive degradation of the material stiffness algorithm under tensile load. The ductile specimen in this study is an aluminum alloy. The progressive failure algorithm used here is based on the assumption that the material behaves like a stable progressively fracturing solid. The stiffness reduction is carried out at the reduced integration gauss points of the finite element mesh depending on the mode of failure. A number of material properties are necessary for such simulation to carry out and experimentation of the metal are needed to evaluate these properties. The actual tensile tests data are applied to the finite element simulation. The verified simulation method has a great importance in practical design of structures and metals. A renowned finite element analysis software ABAQUS is used in this study.

Effect of corrosion damage on seismic behaviour of existing reinforced concrete beam-column sub-assemblages

Environmental degradation of reinforced concrete (RC) in the form of reinforcement corrosion poses greater threat to both strength and serviceability of existing RC structures. If this corrosion damaged structures are situated in the zones of higher seismicity, there would be a great threat to their safety under earthquakes and hence it is extremely important to understand their seismic performance in order to formulate suitable remedial measures. In view of this, in present study, an exterior beam-column sub-assemblage of a residential building is taken up and is designed for two levels, namely (i) designed for seismic load without ductility detailing (non-ductile specimen), and (ii) designed for lower seismic load and with ductility detailing (ductile specimen) to represent the existing RC structures of different design evolutions. Two specimens are cast for each level of design and one specimen from each of these two categories is subjected to accelerated corrosion. The experimental investigations are carried out on the uncorroded and corroded beam-column sub-assemblages under reverse cyclic loading. Corrosion of reinforcement changed the damage progression from joint shear failure to longitudinal and splitting cracking along the reinforcement bars followed by fracturing of corroded reinforcement bars. The corroded specimens showed poor hysteretic performance in the form of huge in-cyclic strength degradation. Furthermore, the cumulative energy dissipated by corroded non-ductile and corroded ductile specimens are respectively only 0.4 times and one-seventh of that of the corresponding uncorroded specimens. Thus, the seismic performance of corrosion affected existing structure is an alarming issue and warrants immediate retrofit intervention.

Rehabilitation of Beam Column joint using Steel Fibrous Concrete

An experimental study was conducted to compare the structural behavior of beam column joint before and after rehabilitation by using fibrous concrete with steel fibers as a strength enhancer material. Two specimens were examined in this study out of which one was designed according to IS 456: 2000 (control specimen) codal provision and another one was designed according to IS 13920:2016(ductile specimen). Both the supports at top and bottom faces of the column were hinged, and the load was applied on the edge of the beam. The parameter observed during the experiment was Load- deflection response for both control and rehabilitation specimens. The ultimate load carrying capacity for rehabilitated controlled specimen increased by 36.6% in comparison with controlled specimen, and the ultimate load carrying capacity for rehabilitated ductile specimen increased by 62.3% in comparison with ductile specimen. It has been observed that steel fiber reinforced concrete can enhance flexural strength, ductility and crack arrest.

A numerical investigation on the effects of rock brittleness on the hydraulic fractures in the shale reservoir

Hydraulic fracturing is an extensively used technique for development of oil and gas resources. In the shale reservoir, rock brittleness plays an important role during hydraulic fracturing. In this paper, a numerical code known as RFPA (Rock Failure Process Analysis) is introduced and the embedded digital-image-based (DIB) technique is illustrated in detail. Based on this integration, the effects of rock brittleness on the failure mode and stress-strain characteristic of the shale specimens are numerically investigated. It is found that the brittle shale specimen is more likely to rupture with multi crossed failure planes while the ductile specimen is more likely to rupture with a penetrating failure plane, from which we deduce the brittle shale is easier to develop more natural fractures than the ductile shale. The influence of natural fractures on complex hydraulic fracture network is further investigated through numerical simulation and the positive effect of rock brittleness is indirectly verified. It is found that hydraulic fractures are preferable to propagate in brittle minerals, i.e. the hydraulic fractures always choose the brittle minerals as the favorite path to propagate or choose a thin or weak part of ductile minerals to penetrate and is blocked by the ductile minerals. Moreover, the hydraulic fractures generated in the brittle shale are tortuous and appear with multi branches, which is much beneficial to form hydraulic fracture network in contrast to the smooth hydraulic fracture generated in the ductile shale. This is probably one of the causes of that the required treatment pressure in ductile shale layer is higher than that in brittle shale layer.

Mechanical Characterization of Austempered Ductile Iron Obtained by Two Step Austempering Process

Austempered ductile iron (ADI) is known to have a good combination of mechanical properties due its unique ausferrite microstructure. The strength of ADI is mainly a function of the austempering temperature and the stability of ausferrite matrix. To increase the stability of the ausferritic matrix, two stage austempering processes was developed. During this investigation, in the Ist step, ductile iron specimens were austenitized at 900 °C for 60 min followed by quenching to 250 °C in salt bath. In the IInd step, after quenching at 250 °C, the salt bath was gradually heated to 350 °C, 400 °C and 450 °C respectively where specimen were soaked for 120 min. The tensile strength and impact strength were evaluated according to ASTM standards. The results were compared with that obtained by conventional austempering process by quenching directly into salt bath at 400 °C for 120 min. Both tensile and impact strength were found to have improved by two step austempering process. During Ist stage of austempering, martensite was observed while during IInd stage of austempering microstructures revealed acicular ferrite and carbon stabilized austenite. The fractographic examination revealed mixed type of fracture mode and intergranular fracture was seen under SEM. It was further observed that the tensile strength decreased whereas the impact strength increased with IInd stage of austempering temperature.