Transverse Tensile Tests Research Articles

Laser-assisted automated tape laying: Effects of placement rate and heated tooling on layer bonding and tensile properties

This paper investigates the processing parameters placement rate and tooling temperature of laser-assisted automated tape laying (ATL). Plates with carbon fiber-reinforced polyether ether ketone (CF/PEEK) were produced at 6 m/min, 9 m/min and 18 m/min, and 23°C and 250°C tooling temperature, respectively. Correlations of processing conditions with micrographs, void content, thickness, the degree of crystallinity and the shear strength of the compression shear test, including a fractographic analysis, were derived. Processing conditions that increase the degree of crystallinity were only found to improve the compression shear strength at 6 m/min placement rates, primarily due to a void content below 3.4 % and degree of crystallinity above 26 %. The fractographic analysis derived from the compression shear test revealed a strong correlation between the degree of crystallinity and the size of ductile drawings. In contrast, the transverse tensile test showed no influences on the ATL processing conditions, whereas the tensile strength in fiber direction decreased by 11 % from a placement rate of 6 m/min to 18 m/min. ATL with a 250°C tooling temperature increased the strengths by 14 % compared to those at room temperature. A further tensile strength improvement of 0° and 90° to 1754 MPa and 75 MPa was obtained by a subsequent out-of-autoclave consolidation using vacuum bagging.

Friction stir welding of 2507 super-duplex stainless steel: feasibility of butt joint groove filling at different process parameters

ABSTRACT The present work explores the feasibility of groove-filling welding of 6 mm-thick 2507 super-duplex stainless steel (SDSS) in a similar butt-joint configuration using friction stir welding (FSW). A 60° V-groove with a 3 mm root face was designed and machined. The FSW trials were performed at varying rotation speeds (400–600 rpm), downward forces (15–25 kN), and a constant travel speed of 25 mm/min using two WC tools with two different cobalt (Co) contents of 8 and 10 wt.%. The groove filling achievements of the welded joints were monitored using three non-destructive tests: visual, penetrant, and radiographic. All the welded joints were subjected to transverse tensile testing in addition to hardness measurements across the joint area. Microstructure and fracture surface characterisation were also investigated to gain insights into the impact of heat input on joint performance through a comparison with the as-received SDSS. Among the trial FSW processes, the results indicate that the FSW parameters of 25 mm/min, 15 kN, and 400 rpm using a WC-8 wt.% Co tool were successfully used to completely fill the groove and produce a defect-free SDSS butt-joint. This joint has the highest average stir zone (SZ) hardness (342 ± 5 HV) and tensile strength (1256 ± 21 MPa) compared to partially jointed specimens.

Flux enhancement with titanium or vanadium oxides addition for superior submerged arc welding of HSLA steel plates

A high-strength low-alloy (HSLA) steel plate of 10 mm thickness underwent submerged arc welding with enhanced fluxes containing additional titanium oxide (TiO2) or vanadium oxide (V2O5). The addition of TiO2 led to the development of a finer acicular ferrite structure but coarsening the carbide and martensite/austenite (M/A) constituents, which marginally improved the hardness, tensile strength, and ductility of weld metal. Conversely, incorporating V2O5 facilitated a substantial vanadium absorption (0.7 wt. %) in the weld metal, giving rise to a distinctive acicular microstructure less reliant on ferrite nucleation at non-metallic inclusions than conventional acicular ferrite. The distinctive microstructure, unique to vanadium steels, combined lath bainite with irregularly shaped granular bainite. The resultant dual-mode bainitic structure, coupled with a more uniform distribution of refined microphase constituents, outperformed the conventional acicular ferrite, delivering more than 20% and 13% improvements in yield and tensile strengths respectively, as evidenced by transverse tensile tests on the weld metals.

Influence of CMT welding parameters on microstructural and properties investigation of dissimilar weld joint for aluminum bronze and carbon steel

Cold Metal Transfer (CMT) welding technology has improved the appearance of weld beads and revolutionized the welding of thicker materials and dissimilar metals with precise metal deposition and reduced heat input. Cold Metal Transfer welding is predominantly used in a variety of industry applications, including aerospace, shipbuilding, automotive and marine industries. In this study, aluminum bronzes and carbon steel were joined by using CMT welding, a variant of the Gas Metal Arc Welding process, with ERCuAl-A2 as the filler metal. Optical microscopy was used to examine the microstructure of the CMT weld joint between aluminum bronze and carbon steel. Results have indicated that dissimilar metals such as aluminum bronze, and carbon steel could be successfully joined by CMT under various processing parameters. The tensile and bending strengths of the dissimilar joint were 490 MPa and 822 MPa, respectively. A variety of intermetallic compounds and solid solutions were generated in the weld zone and fusion zone. The micro-hardness in the carbon steel side of the fusion zones increased sharply, which was 164 HV in the welded condition. The dissimilar joint was stronger than the carbon steel, as the ductile fracture occurred on the carbon steel during the transverse tensile test of the welded specimen. The microstructure interpretation of welded dissimilar joints was analyzed by scanning electron microscopy and transmission electron microscopy.

Bio-Inspired Helicoidal Composite Structure Featuring Graded Variable Ply Pitch under Transverse Tensile Loading

Biostructures found in nature exhibit remarkable strength, toughness, and damage resistance, achieved over millions of years. Observing nature closely might help develop laminates that resemble natural structures more closely, potentially improving strength and mimicking natural principles. Bio-inspired Carbon Fiber-Reinforced Polymers (CFRP) investigated thus far exhibit consistent pitch angles between layers, whereas natural structures display gradual variations in pitch angle rather than consistency. Therefore, this study explores helicoidal CFRP laminates, focusing on the Non-Linear Rotation Angle (NLRA) or gradual variation to enhance composite material performance. In addition, it compares the strength and failure mechanisms of the gradual configuration with conventional helicoidal and unidirectional (UD) laminates, serving as references while conducting transverse tensile tests (out-of-plane tensile). The findings highlight the potential of conventional and gradual helicoidal structures in reinforcing CFRP laminates, increasing the failure load compared to unidirectional CFRP laminate by about 5% and 17%, respectively. In addition, utilizing bio-inspired configurations has shown promising improvements in toughness compared to traditional unidirectional laminates, as evidenced by the increased displacement at failure. The numerical and experimental analyses revealed a shift in crack path when utilizing the bio-inspired helicoidal stacking sequence. Validated by experimental data, this alteration demonstrates longer and more intricate crack propagation, ultimately leading to increased transverse strength.

Micromechanical modeling of longitudinal compression behavior and failure mechanism of unidirectional carbon fiber reinforced aluminum composites involving initial fiber misalignment

AbstractA micromechanical model with realistic initial fiber misalignment (IFM) was developed to simulate the longitudinal compression behavior of unidirectional carbon fiber/aluminum composites. The matrix and fiber were modeled using ductile damage law and brittle fracture model, respectively. The interfacial properties were firstly determined by the single‐fiber push‐out and transverse tensile tests, and the cohesive zone model was adopted to capture the interfacial behavior. The calculated compressive response curve is in alignment with the experimental data. Compression failure can be attributed to fiber kinking, possibly triggered by the matrix shear damage. The increase of IFM angle makes the failure mode being transformed from fiber crushing to fiber kinking, along with a significant decrease in compressive strength. With the fiber content increasing, the compressive strength increases first and then decreases, while the compressive modulus increases monotonically. Increasing interfacial strength significantly improves the compressive strength, but this is limited by the matrix properties.

Multiscale analysis of hierarchical flax-epoxy biocomposites with nanostructured interphase by xyloglucan and cellulose nanocrystals

Natural biological systems feature hierarchical nanostructured architectures achieving high strength and toughness. In this work, the spontaneous adsorption of xyloglucan (XG) and cellulose nanocrystals (CNC) onto flax fabrics is considered to develop hierarchical interphases with improved interfacial adhesion in epoxy-based biocomposites. A multi-scale analysis is carried out, from the nano & micrometric scale with the characterization of fibre surface topography, work of adhesion and interfacial shear strength (IFSS) between flax fibres and epoxy resin, to the macroscopic scale with the transverse mechanical properties of biocomposites. At the fibre scale, XG and CNC increase the surface roughness of flax fibres, as well as their adhesion to epoxy resin with IFSS improved by 60 %, up to 22.3 MPa. At the composite scale, the treatments have a major influence on the cohesion of flax cell walls and microstructure of the biocomposites. Transverse tensile tests reveal both cohesive and adhesive interfacial failure.

Measurement of tensile and shear strength of interfacial bonding in fiber reinforced soft composites combining experiments and simulation

Interfacial bonding strength plays a key role in the mechanical performance of fiber reinforced polymers. However, measurement of interfacial bonding strength in fiber reinforced soft composites (FRSCs) becomes a challenging issue, because the large deformation capability of soft matrix invalidates most of current testing methods. This paper demonstrates an advanced method combining experiments and simulation, which provides a convenient and reliable means to measure both tensile strength and shear strength of interfacial bonding for FRSCs. The specimen is made by embedding a fiber bundle in a soft plate for transverse tensile test. Various stress states along the fiber–matrix interface can be realized by controlling the inclination angle of fiber bundle to the stretching direction. Tensile strength and shear strength of interfacial bonding in FRSCs can be estimated based on the analysis of critical stress states. The comparison with the widely adopted fiber pull-out test indicates that the nominal shear strength obtained in pull-out test is severely underestimated.

Dissimilar friction-stir welding of aluminum alloys 2519, 6061, and 7050 using an additively-manufactured tool

This work was undertaken to evaluate the feasibility of the additively-manufactured tool for dissimilar friction-stir welding (FSW) of 2519, 6061, and 7050 heat-treatable aluminum alloys. The tool design included a flat shoulder with an Archimedean spiral groove and a threaded probe with a Triflute profile. It was found that the application of such a tool provided a nearly twofold decrease in Z-force and essentially enhanced the mechanical mixing of dissimilar materials within the stir zone. Nevertheless, despite the enhancement effect, FSW was inefficient for a homogeneous intermixing of dissimilar materials, and a distinct interface boundary was present within the stir zone. It was also found that the mechanical performance of the welded joints was sensitive to the initial temper condition of the welded alloys. Specifically, FSW of the alloys in the solution-annealed condition provided no significant influence on material strength, while that in the precipitation-hardened state led to significant material softening. During the post-weld T6 treatment, extensive nucleation of silicon-rich particles was found to occur at this interface. It was deduced that those promoted cracking during transverse tensile tests, thus giving rise to the decohesion of the dissimilar welds along the interface boundary. Hence, the post-weld T6 treatment was concluded to be unfeasible for dissimilar aluminum welds.

Effect of welding speed on butt joint quality of laser powder bed fusion AlSi10Mg parts welded using Nd:YAG laser

Abstract The invention of additive manufacturing technology, such as laser powder bed fusion, was initiated by the aerospace industries’ growing need for lightweight alloy components with intricate geometries. However, widespread adoption of lightweight alloy components is limited by size restrictions. Currently, only relatively small and simple-shaped objects can be efficiently produced using lightweight alloys. Thus, this research aims to investigate the effect of welding speed on butt joint quality of laser powder bed fusioned AlSi10Mg parts welded using an Nd:YAG laser. Laser beam welding is a method for welding small parts manufactured by laser powder bed fusion together to build large-scale and complex-shaped objects. Using a 2 kW continuous wave solid-state Nd:YAG laser with three different weld scan speeds (150, 175, and 200 mm min−1), autogenous, single-pass, square butt joints were created from 3 mm thick plates. Crystal orientation mapping and fractography results showed that the laser beam welding scan speed significantly impacts plastic deformation and fracture behavior. A significant amount of grain refinement and an Si-particle morphology change was realized in the weld zone’s microstructure, attributed to the increase in weld scanning speed. The transverse tensile test demonstrates that increasing the weld scan speed from 150 to 200 mm min−1 leads to significant growth in the efficiency of the weld joint, from 70 % to 77 %, arising from grain refinement (13–8 µm). However, a significant decrease in ductility is observed with increasing scan speed. In addition, it was determined that pores have substantial effect on tensile strength and ductility.

Heat management and tensile strength of 3 mm mixed and matched connections of butt joints of S355J2+N, S460MC and S700MC

AbstractHigh‐strength structural steels are beneficial in terms of the sustainability of constructions due to the possible reduction of weight and overall material needs. Nevertheless, high‐strength steels have a smaller processing parameter range in regarding the specific heat input and resulting cooling rate. Especially the cooling time t8/5 characterizing the time span to cool down from 800 to 500 °C is an important indicator. Single layer butt‐welded gas metal arc welding (GMAW) connections of 3 mm plates between normal strength (S355J2+N, S460MC) and high‐strength steels (S700MC) as well as matched connections (S460MC, S700MC) are carried out. Hereby, the influence of the energy input, melting rate, joint preparation, filler metal (matching and undermatching) and backing methods are observed. Spatially resolved IR‐thermal observation shows variations within the welds of up to 50 % in the cooling time t8/5 depending on those parameters. These fluctuations lead to significant changes of the microstructure within the melting and heat‐affected zone. UCI hardness mappings show the softening and microstructural change within these zones. Those soft zones can be the region of failure for butt welded connections as shown by transverse tensile tests with spatially resolved optical strain measurements. The results obtained can be used to define more precise welding procedures of these types of connections and also are used to develop design rules for mixed connections made of normal strength and high‐strength steel.

First Conclusions on Damage Behaviour of Recycled Carbon Staple Fibre Yarn Using X-ray and Acoustic Emission Techniques.

This paper presents the first results on the characterisation of the damage behaviour of recycled carbon fibre (rCF) rovings manufactured into unidirectionally (UD) reinforced plates. In the first step, the mechanical properties of several material combinations were determined by mechanical tests (tensile, flexural, compression). This proves the usability of the material for load-bearing structures. For example, a tensile modulus of up to 80 GPa and a tensile strength of 800 MPa were measured. Subsequently, the fracture surface was analysed by scanning electron microscopy (SEM) to characterise the fibre-matrix adhesion and to obtain first indications of possible failure mechanisms. Despite the high mechanical properties, poor fibre-matrix adhesion was found for all matrix systems. In situ X-ray microscopy tests were then performed on smaller specimens under predefined load levels as transverse tensile and bending tests. The results provide further predictions of the failure behaviour and can be compared to the previous test results. The three-dimensional scan reconstruction results were used to visualise the failure behaviour of the staple fibres in order to detect fibre pull-out and fibre or inter-fibre failure and to draw initial conclusions about the damage behaviour in comparison to conventional fibre composites. In particular, a benign failure behaviour in the transverse tensile test was demonstrated with this procedure. In addition, first concepts and tests for the integration of AE analysis into the in situ setup of the X-ray microscope are presented.

Microstructural features and mechanical behavior of duplex stainless steel/low carbon steel friction stir dissimilar weld

This paper aims to understand the effect of friction stir butt welding on the microstructure and mechanical performance, measured in terms of hardness characteristics, transverse tensile test, and shear punch, of dissimilar weld of duplex stainless steel (DSS) and low carbon steel (LCS). The dynamic recrystallization, material intermixing, and atomic interdiffusion between DSS and LCS governed the microstructure of the stirred zone. The stirred zone was free from harmful intermetallic phases like the sigma phase. It was identified that three distinct metallurgical regions feature the stirred zone, including (i) dual-phase zone (DPZ) with an unbalanced fine duplex microstructure of austenite and ferrite, (ii) ferrite phase zone (FPZ) with fine-grained ferrite strengthened by an enhanced Ni and Cr content, (iii) martensite zone (MRZ), which was formed due to the formation of thermally unstable austenite at high temperatures due to Cr, Ni, and C interdiffusion between DPZ and FPZ. Furthermore, when LCS was positioned on the advancing side, a higher fraction of martensite was formed in the stirred zone due to the more efficient material mixing. The shear punch test indicated that the shear strength of the stirred zone in the dissimilar welds was ∼130% and ∼16% higher than that in the LCS and DSS base metals, respectively. The contributions of solid solution hardening and grain boundary hardening to the hardness/strength of the stirred zone were elucidated.

A multiscale viscoelastic constitutive model of unidirectional carbon fiber reinforced PEEK over a wide temperature range

Due to super toughness and good repairability, the fiber reinforced polyether ether ketone (PEEK) composites are promising to replace metals in the primary-load bearing structures for the next generation aircraft. However, at the high service temperature close to or even above the glass transition temperature of PEEK, composite properties strongly depend on the loading temperature and time, bringing great challenges to their applications. How to evaluate their temperature/time dependent properties over a wide temperature range is the key issue in both the structure design and the process design. This study proposes a multiscale viscoelastic constitutive model for the composites to separately consider the individual contribution of the intrinsic matrix properties and the fiber induced strain concentration. The generalized Maxwell model for the PEEK viscoelastic properties was extended to a three-dimensional case by the genetic integration method. Based on the bottom-up approach, the isotropic viscoelastic matrix and the anisotropic linear elastic reinforcement were considered to construct a multiscale model of the fiber reinforced PEEK composites. To verify the developed model, the unidirectional carbon fiber reinforced PEEK composite samples were fabricated and tested. By the PEEK matrix relaxation tests, the composite transverse tensile tests and the representative volume element (RVE) simulations, the model parameters were calibrated step by step. Good agreements among the experimental results, the RVE simulations, and the model predictions under different tensile states over a wide temperature range (25–200 °C), proved that this model could be used to predict and to design the relaxation behaviors of the fiber reinforced PEEK composites.

Influence of Sizing Aging on the Strength and Fatigue Life of Composites Using a New Test Method and Tailored Fiber Pre-Treatment: A Comprehensive Analysis

Given the time-consuming and complex nature associated with the aging of composites, a novel fabric pre-aging method was developed and evaluated for static and fatigue testing. It allows for investigating sizing and interphase-related aging effects. This fast method is independent of the diffusion processes and the composites’ thickness. Moreover, the new methodology offers enhanced analysis of the sizing, interphase, and fiber-related degradation of composites without aging them by conventional accelerated procedures or under severe maritime environments. For validation purposes, fiber bundle, longitudinal, and transverse tensile tests were performed with five different glass fiber inputs. Significant differences in the durability of composites were found for pre-aging and classical aging, respectively. The impacts of degradation of the single constituents on the fatigue life are identified by cyclic testing of untreated, pre-aged, and wet-aged composites. Here, it is evident that the interphase strength is likewise essential for the tension-tension fatigue performance of unidirectional composites, as is the fiber strength itself. In summary, the presented method provides industry and academia with an additional opportunity to examine the durability of different fibers, sizings, and composites for design purposes following a reasonable methodology.

Effect of thickness on mechanical properties of modified 9Cr 1Mo steel welds made by narrow gap hot wire gas tungsten arc welding process

Hot wire Gas Tungsten Arc Welding (GTAW) process is selected for fabrication of thick section modified 9Cr 1Mo steel components of Steam Generators (SGs) for 500MWe Prototype Fast Breeder Reactor (PFBR) at Kalpakkam, India. During the welding procedure qualification for fabrication of SGs, the 30 mm and 62 mm thick modified 9Cr 1Mo steel welds were subjected to chemical analysis, visual examination, liquid penetrant examination, radiography examination, micro-hardness tests, longitudinal and transverse tensile tests (at ambient temperature and 525 °C), bend tests, drop weight tests and impact tests (at 0 °C and +18 °C). Literature reveals both positive and negative view on the welding of thick section steel components. Limited information is available in open literature on the effect of thickness on material properties of modified 9Cr 1Mo steel welds made by hot wire GTAW method. In view of the above, authors attempted to systematically investigate the influence of thickness on mechanical properties of modified 9Cr 1Mo steel welds made by hot wire GTAW process. In this paper, the chemical compositions, hardness, tensile strength, bending strength and impact properties of 30 mm and 62 mm thick welds produced by narrow gap hot wire GTAW process are characterized and compared. It is found that the mechanical properties of 30 mm and 62 mm thick welds are comparable except the impact properties at 0 °C. The impact strength at 0 °C for 62 mm thick weld was found inferior in comparison with 30 mm thick weld.

Mechanical Properties and Bonding Mechanism of the Mg/Al Clad Sheet Manufactured by the Corrugated Roll

In this research, corrugated Mg/Al clad sheet with good interface bonding was prepared with a rolling mill of upper corrugated roll and a lower flat roll under the conditions of 35% reduction and 400 °C. The mechanical properties of the corrugated Mg/Al clad sheet were studied using the transverse tensile test, Vickers microhardness and as well as its bending properties. Moreover, the interface bonding mechanism of the corrugated clad sheet was researched through three-dimensional contour analysis. The results showed that the UTS at the trough position was the highest (~296 MPa), and that the peak position was the lowest (~257 MPa). The maximum fracture EL at the peak position was ~13.4%, while the minimum fracture EL at the trough position was ~10.6%. In the transverse tensile process, the interface cracked first due to the uneven stress distribution in the matrixes. Then, the Mg sheet broke, and finally the Mg/Al clad sheet failed with final fracturing of the Al sheet. The microhardness of interface metal Al at the four positions was higher than that of the interface metal Mg, which was closely related to the dislocation strengthening of the Al sheet. The interface bonding mechanism of the corrugated Mg/Al clad sheet could be divided into four stages: extrusion deformation, rubbing fracture, compound extension and compound completion.

Deep drawability of electron beam welded tailored blanks of commercially pure titanium thin sheets

In this work, commercially pure titanium tailor-welded blanks (TWBs) were fabricated from sheets of thicknesses 1.0 mm (Ti1.0) and 1.2 mm (Ti1.2) using electron beam welding (EBW). It was observed that the titanium base materials had an equiaxed microstructure, whereas the FZ of the weld consisted of coarsened prior β grains with internal α substructures. Transverse and longitudinal tensile tests were conducted to evaluate weld integrity and weld properties, respectively. The deep drawing behaviour of both the base materials and TWB had been investigated by conducting laboratory-scale deep drawing tests. The limiting drawing ratios (LDR) of the Ti1.0 and Ti1.2 base materials were 2.14 and 2.21, respectively. The LDR of TWB was 2.14, which was same as that of the Ti1.0 base material. The CPB06 yield criterion and weld properties were incorporated in the FE modelling to study the deep drawing behaviour of the TWB for the first time. The FE model successfully predicted the non-uniform material flow and thickness distribution in the deep drawn TWB. Moreover, the weld line movement was found to be towards the Ti1.0 side at the cup top region and towards the Ti1.2 side at the cup bottom of the TWB deep-drawn cup.

Grey model prediction for the interfacial properties of carbon fiber-reinforced bismaleimide resin under thermo-oxidative aging

The overall performance of composites will be seriously affected when their interfacial properties degrade after thermo-oxidative aging (TOA). In this paper, the interfacial properties of carbon fiber (CF)/bismaleimide (BMI) resin aged for 10, 30, 90, 120 and 180 days at 200°C and 250°C were quantitatively studied by transverse fiber bundle tensile (TFBT) testing. In addition, a prediction model of interfacial strength based on the grey model theory was established. The results show that the interfacial strength for CF/BMI resin decreases exponentially with the extension of aging time, and the strength of the TFBT specimens aged at 200°C for 180 days and 250°C for 90 days decreases by 82.01% and 84.65%, respectively. This is caused by the oxidation decomposition of BMI resin and the mismatch of the thermal expansion coefficient between the CF and BMI resin. In addition, the grey model is used to predict the interfacial properties of CF-reinforced BMI resin under TOA. The prediction accuracy is higher than that of the traditional exponential model, and the prediction error is less than 10%. To sum up, this work can provide a reference for studying the evolution of interfacial properties of other kinds of fiber-reinforced polymer composites under extreme environments.

Direct measurement and verification of cohesive zone model parameters for basalt/PProds using the transverse tensile test and virtual double cantilever beam test

AbstractTo further our understanding of failure in thermoplastic‐based composite rods, the mode I‐governed cohesive zone model parameter of a basalt fiber reinforced polypropylene composite rod is evaluated. The relations between stress and strain, the maximum normal traction and final separation displacement are examined using a transverse tensile test method. The measured traction is verified by three‐dimensional finite element analysis of rod‐shaped double cantilever beam specimens. The numerical results show the close relation between the crack length and cube root of compliance, and yields a representative value of the mode I‐governed critical fracture energy.