T-shaped Specimens Research Articles

Axial compressive behavior of T-shaped welded multi-partition composite members

T-shaped welded multi-partition composite members, which are made of several rectangular concrete-filled steel tubes, are proposed to speed up the fabrication procedure. Seven half-scale T-shaped specimens were tested by considering the section height-to-width ratio and slenderness ratio. In the test, a slight torsion angle was measured when the instability failure along the asymmetric axis occurred, indicating the specimens had good torsion resistance. When the relative slenderness ratio of the specimen was larger than 0.44, the specimens failed due to the instability along the asymmetric axis. Parametric numerical analysis is conducted by considering the slenderness ratio, cross-section dimension, steel ratio, and material strength. The results show that the strength of concrete negatively impacts the ductility of the specimens, leading to a decrease of 43%, while the strength of the material positively influences the stability of the specimens. The formulas from different traditional codes are verified by the parametric numerical analysis results, indicating most codes can conservatively predict the sectional bearing capacity, but overestimate the stability coefficient of the specimens by neglecting the reduction effect of the excessive height-to-depth ratio. Recommendations are provided for calculating the stability coefficient under axial compression applicable to T-shaped welded multi-partition composite members.

Semi-Analytical Solution Model for Bending Deformation of T-Shaped Aviation Aluminium Alloy Components under Residual Stress

Structures composed of aviation aluminium alloys, characterized by their limited rigidity and thin-walled configurations, frequently exhibit deformation after processing. This paper presents an investigation into T-shaped components fabricated from pre-stretched 7075-T7451 aviation aluminium alloy sheets, examining the effects of residual stress and the geometrical parameters of T-shaped components on their deformational behavior. A semi-analytical model, developed to elucidate the bending deformation of T-shaped components subjected to residual stress, was validated through finite element analysis and empirical cutting experiments. The experimental results revealed that the bending deformation deflection of the T-shaped specimen was 0.920 mm, deviating by a mere 0.011 mm from the prediction provided by the semi-analytical model, resulting in an inconsequential error margin of 1.2%. This concordance underscores the precision and accuracy of the semi-analytical model specifically designed for T-shaped components. Moreover, the model’s simplicity and ease of application make it an effective tool for predicting the bending deformation of thin-walled T-shaped components under a range of residual stresses and dimensional variations, thereby demonstrating its significant utility in engineering applications.

Failure in co-cured composite joints enhanced with J-272 film

Lightweight and high strength CFRP material has been applied to airspace industry to realize lightweight aircraft. Nowadays, composite T-joint is a common adhesive joint type used in aircraft CFRP load-bearing structure. This study employed T300/7901 prepreg and J-272 film as the adhesive in the deltoid of T-joints, and produce T-shaped specimens via co-curing. The start point of failure location is located at deltoid through pull-off test combined with digital image correlation system. In the pull-off test, the failure of the T-joint specimen, the deltoid of which was filled with T300/7901 prepreg and J-272 film, exhibited progressive failure mechanism from rib web to skin. Compared to adherence with T300/7901 prepreg, the initial failure load and toughness of composite T-joints adhered with J-272 film were increased 24.3% and 34.7%, in which J-272 film boosted the interfacial binding between the rib web and the skin.

Seismic behavior along the asymmetrical axis of T-shaped multi-partition steel–concrete shear walls

Five specimens have been tested under cyclic lateral loads to explore the seismic behavior of T-shaped multi-partition steel–concrete shear walls along the asymmetrical axis. The loading has been applied by considering the torsion effect from non-coincidence between the lateral loads and the shear center in this study. The main parameters of the test are the axial compression ratio and section height-to-breadth ratio aiming to study the vertical load and web constraint effect. The test results indicate that the failure mode of all specimens along the asymmetric axis is bending failure with minor shear deformation measured during loading. The yield drift (1/138) and the ultimate drift (1/41) of the T-shaped multi-partition steel–concrete shear walls could meet the requirement of the corresponding code, namely 1/350 and 1/70, respectively. The increase in axial compression ratio increases the out-of-plane displacement but decreases the ductility of the specimens, whilst the increase in section height-to-breadth ratio decreases the out-of-plane displacement of the specimens. The relatively small torsion angle of less than 0.6° indicates that the T-shaped multi-partition steel–concrete shear walls have good torsion resistance. Under the cyclic lateral loads along the asymmetrical axis, the out-of-plane displacement of the T-shaped specimen will occur on the side without the web. The web elastic stress distribution model can predict the lateral resistance more accurately, whilst the full-section plastic stress distribution model overestimates the lateral resistance of T-shaped multi-partition steel–concrete shear walls.

Seismic performance and shear lag effect of T-shaped steel plate reinforced concrete composite shear wall

This research introduces an experimental test and finite element method to study the seismic performance and shear lag effect of T-shaped steel plate reinforced concrete composite shear walls (SPRCWs). Low-cycle cyclic loading tests were conducted on five T-shaped specimens and one conventional rectangular specimen, with axial compression ratio, shear span ratio, and geometric dimensions of web and flange as the primary test parameters. The test results demonstrated that the specimens showed bending, bending-shear, and shear failure modes depending on the shear span ratios, with T-shaped specimens exhibiting more satisfactory seismic behavior than the rectangular specimen. Furthermore, the T-shaped specimens showed better seismic behavior under compression in the flange than under tension. Smaller axial compression ratios and web lengths, as well as greater flange widths, resulted in better deformation capacity and energy dissipation capacity, and the bearing capacity was enhanced by increasing the axial compression ratio and web length. Test results were used to investigate the shear lag effect of T-shaped SPRCW, and a parametric study was performed using ABAQUS to examine the impact of various design parameters on the shear lag effect. The simulation results indicated that increasing the wall height and steel plate ratio in the flange, and reducing the flange width could significantly weaken the shear lag effect. In contrast, the web length and axial compression ratio have little effect on the shear lag effect.

Study on Hydro-Mechanical Coupling Failure and Permeability Enhancement Mechanisms for Sandstone with T-Shaped Fractures.

The rise in the connectivity of the fractures is a key task in oil/gas and geothermal exploitation systems. Natural fractures widely exist in underground reservoir sandstone, while the mechanical behavior of rock with fractures subjected to hydro-mechanical coupling loads is far from clear. This paper employed comprehensive experiments and numerical simulations to investigate the failure mechanism and permeability law for sandstone specimens with T-shaped faces subjected to hydro-mechanical coupling loads. The effects of crack closure stress, crack initiation stress, strength, and axial strain stiffness of the specimens under different fracture inclination angles are discussed, and the evolution processes of permeability are obtained. The results show that secondary fractures are created around the pre-existing T-shaped fractures through tensile, shear, or mixed modes. The fracture network causes an increase in the permeability of the specimen. T-shaped fractures have a more significant effect on the strength of the specimens than water. The peak strengths of T-shaped specimens decreased by 34.89%, 33.79%, 46.09%, 39.32%, 47.23%, 42.76%, and 36.02%, respectively, compared with intact specimen without water pressure. With the increase in deviatoric stress, the permeability of T-shaped sandstone specimens decreases first, then increases, reaching its maximum value when macroscopic fractures are formed, after which the stress suddenly decreases. When the prefabricated T-shaped fracture angle is 75°, the corresponding permeability of the sample at failure is maximum, with a value of 15.84 × 10-16 m2. The failure process of the rock is reproduced through numerical simulations, in which the influence of damage and macroscopic fractures on permeability is discussed.

Experimental and numerical investigation of stringer’s 90° plies optimization of composite material stiffened panels

In this paper, the optimal design of I- and T-shaped stringer’s 90° plies is investigated to improve the performance of composite stiffened panel’s strength and curing deformation. A theoretical method is deduced to build the constitutive equations of curing and buckling, which indicates that the stringer’s 90° plies play an important role in the curing deformation of the structure. The finite element method (FEM) is adopted to simulate the curing and instability path of the structure, and the simulation model’s accuracy is verified by strain assurance criterion. In addition, the experimental analysis is performed by a series of I- and T-shaped specimens with different stringer’s 90° plies. The good agreement between the results of theoretical method, FEM, and experiment confirms the reliability and feasibility of the analytical methods proposed in this paper. Furthermore, the optimal stringer’s 90° plies ratio is explored. The curves fitted in this investigation reveal that in the stages of (I) and (II), the percentage of stringer’s 90° plies θ has significant effect on curing deformation, while bearing capacity has little change. The reasonable range of θ is 5%∼20%, in which the bearing capacity and curing deformation reach the optimal solution. Therefore, the structures that are not sensitive to curing deformation are recommend to remove the stringer’s 90° plies, which is benefit to reduce weight, optimize structural design and improve process quality. The results provide a reference to design I-, T-, L- and C- shaped composite panel.

Experimental and theoretical study on seismic behavior of slab-wall joints in a new large-span slab-shear wall structural system

This paper proposes a new structural system named large-span slab-shear wall structure, which has prominent advantages in the architectural function and structural construction compared to the traditional shear wall structure. Due to the larger span and greater thickness of slabs, as well as the elimination of many beams and internal walls, the thick slab-shear wall joint becomes a key component in the new structure. This paper focuses on three typical types of thick slab-shear wall joints and conducts cyclic loading tests to reveal their seismic performance, including the exterior joints on the top floor (three l-shaped specimens), exterior joints on the intermedia floors (two T-shaped specimens), and interior joints on the top floor (two T-shaped specimens). Variables including the anchorage method of the slab bars and the reinforcement ratio of the walls are studied. Thereafter, based on the test results, a new calculation method for the joint strength of the slab-wall joints is proposed based on the strut-and-tie model from ACI318-19. The test results demonstrate that the proposed three types of slab-wall joints exhibit adequate strength and ductility under seismic loading despite the joint shear failure. The proposed simplified anchorage method can greatly reduce the congestion in the joint zone without weakening the seismic performance. The strut-and-tie model can provide an accurate prediction for the shear strength of the slab-wall joint zone.

Behavior of concrete-filled T-shaped steel tubular beam-columns under biaxial compressive loads

Concrete-filled T-shaped steel tubular (CFTST) columns have a wide prospect of being used in high-rise buildings to avoid having protruding portions in walls. This paper presents an experimental and theoretical study on CFTST beam-columns under biaxial compressive loads. Five full-scale CFTSTs, including an axially loaded column and four biaxially loaded beam-columns, were tested and the failure modes, lateral deflections and strains were discussed. Current design methods originally for rectangular CFSTs offered a much conservative prediction for the tested T-shaped specimens as the cross-section is single-symmetric. Based on fiber element analysis, parametric study was conducted to investigate the effects of key parameters on the interaction curves that were normalized by the moment capacity of the specimen under uniaxial eccentric compression. Concrete strength, steel yield stress and steel tube thickness have insignificant effects on the normalized interaction curves but the influences of axial force ratio, cross-section dimensions and slenderness ratio are obvious. Finally, empirical interaction formulas in both complex and simplified forms were proposed for CFTSTs under biaxial eccentric loads. Accuracy of the proposed method was then verified by the experimental results and fiber element analysis results.

Development of a novel method for measuring the interfacial bonding strength of laser cladding coatings

Interface bonding strength is a crucial factor that determines the final mechanical properties and performance of laser cladding coatings. Due to the metallurgical bonding caused by laser cladding, the traditional method of measuring normal interface bonding strength is difficult to use. The present paper proposes a self-designed T-shaped sample and related fixtures to characterize the interface bonding strength. Tensile tests are performed on T-shaped specimens with different cross-sectional areas, and one of the shapes is used for subsequent testing. The fracture morphology of the T-shape samples presented obvious dimples and cleavage steps at the fracture, indicating that the fracture mechanism is hybrid fracture. When the laser power is 2200 W, the T-shaped sample has a higher interface bonding strength of 637 MPa. The effectiveness and repeatability of the method are proved by comparative experiments. This study provides new insights into the better evaluation of laser cladding interface bonding strength in engineering applications.

Flexural Behavior of UHPC Beams Prestressed with External CFRP Tendons

This paper presents an experimental investigation on the flexural behavior of ultra-high-performance concrete (UHPC) beams prestressed with external carbon fiber-reinforced polymer (CFRP) tendons. A total of eight T-shaped beam specimens were fabricated and tested, and the effects of the effective prestressing stress, partial prestressing ratio, deviated angle, and loading condition on the flexural behavior were analyzed. The experimental results indicate that the fully prestressed beams experienced a brittle failure, and the shear capacity of these beams was mainly controlled by the effective prestressing stress in CFRP tendons and the ultimate tensile strength of UHPC, whereas the partially prestressed beams failed in a ductile manner. The presence of internal steel reinforcement could significantly improve the flexural capacity and deformation ability. Thus, internal reinforcements should not be omitted from UHPC beams with CFRP tendons. A higher effective prestressing stress resulted in enhanced cracking load and flexural capacity. The deviated angle enhanced the utilization efficiency of high strength CFRP tendons. The loading condition exerted a slight influence on the flexural behavior of the specimens. Moreover, a method considering the effect of steel fibers was proposed and verified to predict the flexural capacity of UHPC beams prestressed with external CFRP tendons.

Revealing ductile/quasi-cleavage fracture and DRX-affected grain size evolution of AA7075 alloy during hot stamping process

The microstructural evolution, including ductile fracture modes and grain size at elevated temperature, exhibited significant effects on the macroscopic rheological behaviour and restricted the formability of the high-strength AA7075 alloy employed in the hot stamping process. In this study, AA7075 alloy was subjected to uniaxial hot tensile tests at deformation temperatures of 350–450 ℃ and strain rates of 0.01–1 s−1 to analyse the thermal rheological behaviour, damage and grain size evolution, in tandem with the preferred grain orientations affected by intergranular and intracrystalline evolution. A set of improved viscoplastic damage constitutive models was established, which consider the combined interactions of dislocation density and grain size as well as the ductile and quasi-cleavage fracture modes, to elaborate and reveal the fracture modes and grain size evolution of AA7075 alloy during the hot stamping process. Particularly, the evolution of dislocations accumulation was established incorporated with DRX-affected grain refinement. Subsequently, the material parameters were determined and calibrated based on a genetic algorithm, and the feasibility of the constitutive model was verified by simulations of uniaxial tension experiments. Finally, a finite element (FE) simulation of a hot formed T-shaped specimen was carried out. The mesoscopic and macroscopic deformation behaviours, including the evolution of grain size, damage and thickness distribution, were predicted, and the influences of grain size and damage on the formability were explained. Especially it was found that the grain size of the T-shaped components at the punch fillet was the largest, while the grain size at the bottom of the T-parts was the smallest. In addition, severe thinning region of T-shaped parts possess the largest normalized grain size. This study provides theoretical guidance and a scientific basis for the application and forming control of AA7075 alloy in hot stamping processes.

Effect of laser power on microstructure and interfacial bonding strength of laser cladding 17-4PH stainless steel coatings

17-4PH stainless steel coatings is widely used in the field of laser repair due to its excellent performance. In the service process, the coatings not only have excellent mechanical properties but also ensure the formation of an excellent metallurgical bond between the coatings and the substrate. In this paper, the formability, microstructure evolution, texture characterization, microhardness and interface bonding strength of laser cladding 17-4PH stainless steel coatings under different laser powers are studied. A novel test method and related fixture are designed to analyze the interface fracture behavior of T-shaped specimens and evaluate the bonding strength. The relationship between microstructure and interfacial bonding strength of T-shaped specimens is investigated by electron backscattering diffraction (EBSD) and a universal testing machine. The higher stress concentration at the interface and heat-affected zone has been found by comparing the coatings. When the laser power is 2200 W, the microhardness and interfacial bonding strength are higher than other specimens, which are 450 HV and 908 MPa, respectively. This phenomenon is due to the appropriate laser power refines grains and reduces micro defects at the interface, which all contribute to improving the interfacial bonding strength. Fracture analysis shows that the combination of microvoids and unmelted powder contributed to accelerating the propagation of cracks.

The mechanical response of additively manufactured IN625 thin-walled structures

Additive manufacturing offers enhanced design and topological complexity over traditional manufacturing and is well suited to fabricate complex structures. Here, we present a new milli-scale test method to assess the location-specific mechanical response of laser powder-bed printed Inconel 625 thin-walled structures. High-resolution digital image correlation was coupled with ambient temperature milli-scale tests to understand the progression of plastic deformation in T-shaped specimens. Plastic strains were concentrated around the intersection of the horizontal and vertical ligaments, emphasizing their importance in the design process. EBSD scans elucidated the role of geometry in the development of in-plane texture. Isotropic finite element models were unable to fully predict the response of printed specimens, but anisotropic models, motivated by the texture measurements, resulted in much better agreement. This work illustrates the importance of local processing and microstructure on the mechanical response of additively manufactured components.

Experimental seismic behavior of T-shaped double skin composite wall with steel truss

The double skin composite wall (DSCW) with steel truss is an innovative lateral load resisting member which composed of two steel plates, core concrete, concrete-filled steel tubes (CFSTs) as boundary members, and steel truss connectors. The effects of the aspect ratio and the flange wall width on the seismic performance are investigated based on the quasi-static test of full-scale T-shaped DSCWs with steel truss. The failure mode, load-displacement response, shear strength, ductility, energy dissipation, shear deformation, and stress distribution of the specimens were analyzed. The test results showed that the failure mode of the T-shaped DSCW with steel truss specimens with aspect ratios of 2.0 and 2.5 was flexure-shear failure, which was characterized by shear buckling of the steel plate, local buckling, and fracture of the boundary members, and of crushing of core concrete. The T-shaped specimens with a small aspect ratio have a higher shear strength, ductility, energy dissipation capacity, and shear deformation proportion. The T-shaped specimen with a long flange wall also has a higher shear strength, but the ductility, energy dissipation capacity, and shear deformation proportion are small. The stress distribution indicates that the T-shaped specimen is more likely to failure due to the insufficient flexural strength of the boundary member. The theoretical formula for the flexural strength of T-shaped DSCW with steel truss is established, and the validation results show that the formula is accurate and safe.

The use of effective full penetration of T-butt welds in welded moment connections

Full-penetration butt welds are often specified to connect the beam flanges to the column flange in welded moment resisting connections. Partial-penetration butt welds are cheaper than full-penetration butt welds and also more cost effective when compared to large fillet welds. EN 1993-1-8 standard includes a definition of an “effective full penetration of T-butt welds” implying that it can be used to replace butt welds leading to cost savings. This study evaluates the seismic performance of welded beam-to-column connections using effective full penetration of T-butt welds. Three full-scale T-shaped specimens were tested under cyclic loading. The results demonstrate that the effective full-penetration butt welds work very well under seismic loading, forcing the failure mode into the beam and enabling considerable energy to be dissipated within the beam plastic hinge, with no failure in the beam to column welds. Mock-up specimens were fabricated under real workshop conditions to examine the feasibility of reliably fabricating the weld penetration profiles required by EN 1993-1-8. This paper makes recommendations to the use of “equivalent strength” partial-penetration butt welds that can be used by the designer and/or fabricator to replace full-penetration butt welds.

Experimental and Numerical Study on Methods of Testing Withdrawal Resistance of Mortise-and-Tenon Joint for Wood Products

Withdrawal resistance of the mortise-and-tenon (M&T) joint is an important indicator to evaluate the strength of the M&T joint. Generally, the T-shaped specimen is usually used to measure withdrawal resistance using tensile methods, but there has not been testing standard until now. In this study, the methods of measuring withdrawal resistance of the M&T joint were investigated systematically. A new method used to determine the withdrawal resistance of M&T joint was proposed to be named as the compressive method. In addition, withdrawal resistances of M&T joint determined using tensile and compressive methods were compared based on experiments and the finite element method (FEM). The experimental results showed that the effects of the testing method and glue on withdrawal resistance of M&T joint were statistically significant, specifically, the withdrawal resistance measured using tensile method was higher than the one determined by the compressive method. Meanwhile, the results of FEM also confirmed the experimental results in a visible way. The results of FEM indicated that the withdrawal resistance of the M&T joint was influenced by tenon member length; specifically, the withdrawal resistance of the M&T determined by tensile method increased with the increasing of tenon member length. In summary, the results of the study make sense in the measurement of withdrawal resistance of the M&T joint in practice, and in f theory, the study will contribute to instructing the design of furniture structures.

Active Monitoring of Fatigue Crack in the Weld Zone of Bogie Frames Using Ultrasonic Guided Waves.

The bogie frame is an important structure of railway vehicles, transmitting the traction, braking force, lateral force, and vertical force during the traction operation. With the development of high speeds and heavy loads, the appearance of fatigue cracks in the bogie frames is increasing, which reduces the driving life of railway vehicles and even causes serious traffic accidents. Real-time monitoring on the integrity of the bogie is an inevitable requirement for ensuring the safe operation of railway vehicles. In this paper, ultrasonic guided wave-based active structural health monitoring (SHM) was developed to identify the fatigue crack of the bogie frame. Experiments were conducted on a welded T-shape specimen with a thickness of 12 mm. A total of 10 piezoelectric lead zirconate titanate (PZT) disks were mounted around the weld zone of the specimen, five of which were used as actuators, and the other five were used as sensors. Five-peak modulation narrow-band sine waves were input into the actuators to excite the specimen. From the sensor signals, the advanced damage index (DI) was calculated to identify the propagation of the crack. The experimental results demonstrate that crack damage as small as 2 mm in the weld zone of the bogie frame can be successfully detected. Some practical issues for implementing the SHM in real applications, such as crack quantification and environmental compensation, were also discussed.

A finite element model of semi-rigid mortise-and-tenon joint considering glue line and friction coefficient

The aim of this study is to build a new numerical model of a mortise-and-tenon joint based on the finite element method (FEM) considering glue line and friction coefficient to analyze the semi-rigid wood joint. Firstly, the friction coefficient, glue distributions and strengths of the mortise-and-tenon joint were determined by experimental methods. Secondly, these parameters were specified to a T-shaped mortise-and-tenon joint model to build a finite element model of joint by FEM. Finally, both withdrawal and bending load capacity of T-shaped specimens were investigated by experimental and numerical methods. The results showed that the testing methods used to determine the coefficient, distributions and strengths of the glued mortise-and-tenon joint were all effective enough to determine the mechanical properties of the wood mortise-and-tenon joint, and the finite element model of joint can be applied to analyze the semi-rigid mortise-and-tenon joint with consistency beyond 85%. These methods and finite element models will contribute to the analysis of wood products and wood constructions.

Normal Stiffness model of bolted joint based on the modified three-dimensional elastic-plastic contact fractal model

Bolted joints have a significant effect on the dynamical behaviour of assembled structures. Accurate contact stiffness model of bolted joint is crucial in predicting the dynamic performance of bolted structures. In this research, a modified three-dimensional fractal model of normal contact stiffness is presented to more accurately predict the dynamic characteristic of a bolted assembly. In the present model, while the contact deformation exceed the critical value the elastic-plastic contact is used to take the place of Hertz elastic contact in the traditional M-B model, and revise the drawback that elastic-plastic contact occurs before elastic contact in existing elastic-plastic fractal models. As the increase of contact force, the plastic deformation of single asperity is considered again, which is omitted in the two type fractal models. An experimental set-up with two T-shaped specimen is designed conducted to verify the efficiency of the proposed model. Comparing with the ZX elastic-plastic fractal model, the present model can predict contact stiffness and dynamic performance more accurately, particularly, while for higher contact loads. The results show that the modified elastic-plastic fractal contact model can be used to more accurately predict the stiffness and dynamic characteristic of bolted structures in the machine tools.