Pre-drilled Holes Research Articles

Influence of predrilled holes in the upper sheets on the formability and bearing capacity of self-piercing riveted bonded structural components

Self-piercing riveted bonded (SPRB) joints have been widely used in the automotive manufacturing industry, and it was interesting to find that the joint performance was greatly improved by predrilling holes in the upper sheets. The predrilled hole diameters (1.0 mm, 2.0 mm, 3.0 mm, 4.0 mm, and 5.4 mm) in the upper sheet of joints were prepared, and the corresponding joints were named PSPRB-D1, PSPRB-D2, PSPRB-D3, PSPRB-D4, and PSPRB-D5, respectively. Numerical and experimental results showed that the bonding area of joints increased due to the adhesive flowing into the rivet cavity through the predrilled holes. As the diameter of the predrilled hole increased, the stiffness of the trapped upper sheet gradually decreased. Rivets were easier to pierce the upper sheet and insert longer into the lower sheet, together with the supporting effect of the upper sheet trapped steel, resulting in the mechanical interlock of joints increasing, followed by decreasing. The mechanical properties of PSPRB-D3 joints were better than others under lap shear and pull-out loading conditions. The peak force and energy absorption of PSPRB-D3 joints were improved by 12.79 % and 35.71 % at most as compared with those of the SPRB joints, respectively. This was due to the increased mechanical interlock of the joint and the additional bonding reinforcement. However, the strength of PSPRB-D1 joints improved little due to the insufficient filling of adhesive, while the strength of PSPRB-D4 and D5 joints was significantly decreased due to the inadequate stiffness of the upper sheet trapped steel and the smaller mechanical interlocks. Moreover, two box-beam structural components containing SPRB and PSPRB-D3 joints were prepared. The one with PSPRB-D3 joints showed higher mechanical properties in the experimental test. The peak force and energy absorption increased by 15.21 %−22.42 % and 12.01 %−13.01 %, respectively, compared to those of the SPRB structural components. The proposed predrilling hole process improved the thickness distribution of the adhesive layer of the SPRB joints and provided guidance for the connection of structural components with high requirements for joint bearing capacity.

Active and Passive Filling Stir Repairing of AISI 304 Alloy

This study investigates active filling friction stir repair (AF-FSR) and passive filling friction stir repair (PF-FSR) for repairing AISI 304 stainless steel sheets, focusing on addressing the challenges posed by high melting point metals. The research involved repairing overlapping 2 mm thick sheets with pre-drilled holes of 2, 4, and 6 mm diameters, simulating broken components. Various process parameters, including rotational speed, dwell time, and the use of metal fillers, were tested to evaluate their impact on repair quality. The results demonstrated that PF-FSR provided superior mechanical strength to AF-FSR, particularly for larger pre-hole diameters. PF-FSR achieved higher shear tension strength due to better defect filling and reduced void formation, with shear tension strengths exceeding 25 kN for larger pre-holes and lower variability in strength measurements. AF-FSR was less effective for larger pre-holes, resulting in significant voids and reduced strength. Microstructural analysis revealed that PF-FSR facilitated more efficient material mixing and filling, minimizing unrepaired regions. However, excessive rotational speeds and dwell times in PF-FSR led to deformation and flash formation, highlighting the need for optimal parameter selection. Although further studies are needed, this study confirms the feasibility of FSR techniques for repairing small defects in AISI 304 steels, offering valuable insights for sustainable manufacturing practices in industries such as automotive and aerospace, where efficient and reliable repair methods are critical.

Ultimate strength and design of CFDST columns with intermittent welded plate stiffeners

This study conducts an experimental investigation and formulates a finite element model and design equation to determine the ultimate strength of concrete-filled double-skin tubular (CFDST) short columns. These columns are equipped with intermittent welded plate stiffeners, and the welding is performed on the inner surface of the outer tube through pre-drilled holes at intervals of 10 t, 20 t, 30 t, and 40 t, where “t” represents the thickness of the outer tube. The study investigates the behaviour of the CFDST column influenced by the presence of plate stiffeners, determines the axial strength of eighteen CFDST specimens and discusses the load-displacement curve, deformation and ultimate strength. The findings demonstrated that the ultimate load of the plate-stiffened CFDST columns is between 24% and 42% higher than the unstiffened CFDST columns. The plate-stiffened CFDST columns also exhibited higher ultimate strength at the smallest weld spacing of 10 t. The experimental results showed that the plate stiffeners influenced the distribution of the internal forces, which changed the effective confinement area of the concrete. The investigated force distribution provides a fundamental theoretical basis for computing the confinement area for the finite element model (FEM) and design model. This study developed a verified nonlinear FEM that employed ABAQUS to replicate the behaviour of the plate-stiffened CFDST columns. Finally, this study proposes a new design model that considers the effective cross-sectional area of the concrete confined in CFDST columns with intermittent welded plate stiffeners. The strength predictions of the plate-stiffened CFDST columns were accurate compared to the experimental results.

Dynamic responses and failure behaviors of submerged reefs containing pre-drilled hole subjected to repetitive impacting

The drilling-hammer method is adopted for the breaking over submerged reefs in waterway regulation engineering. However, rocks with pre-drilled holes are highly susceptible to the repetitive impacts from drop hammers or drilling equipment. Exploring the dynamic responses and failure behaviors of drilled-hole rocks under repetitive impacting is important for promoting implementation of this technique. In this study, the repetitive impacting tests were conducted on the drilled rocks by the split Hopkinson pressure bar to investigate the rock bearing capacity, deformation property, failure behavior, and energy evolution. The results indicate that the presence of pre-drilled holes and the decreasing loading rates attenuate the bearing capacity of rocks subjected to repetitive impacting. In contrast, the rock deformation capacity is impacted subtly by the impact loading rate and increases with the number of impacts and borehole size. The drilled rock failure occurred with the prevalence of intergranular fractures; subsequently, the proportion of transgranular fractures increased, contributing to the loading rate-dependent bearing capacity. The inverted S-shaped damage evolution curve was assessed using the inverted logistic growth model. The specimen absorbed few incident energies for fracture generation and propagation, and the rock with a larger drill size displays higher energy utilization and larger fragments.

Exploring Stresses in Mandibular Jawbone during Implant Insertion: A Three-Dimensional Explicit Dynamic Analysis

In dental implant insertion, an artificial foundation is prepared for the prosthetic device, which involves the surgical positioning of the implant in the jaw bone. The success of dental implants relies on the osseointegration process. The biomechanical factors, such as stress and strain, developed during the insertion affect the jawbone and its surroundings. In this current study, the stresses during the implant insertion in the mandibular jawbone bone are analyzed using three-dimensional explicit dynamic analysis, and the Cowper–Symonds model is implemented with the damage model. The implant’s design has a substantial impact on stress distribution within the cancellous bone during the insertion procedure. The stress variation takes place as the implant moves into the pre-drilled hole. This is because of the contact between the bone and the fixture on the implant. The upper edge of the predrilled site shows that the stresses are more at the crestal region of the implant due to surface area. There is a gradual increase in the stress level as the implant reaches the lower edge from the top edge. This is because of the concept of mechanical interlocking. Clinicians can use this information to anticipate and address potential stress-related challenges during implant placement.

An experimental and numerical study on the shear performance of friction-type high-strength bolted connections used for CLT-steel hybrid shear walls

One type of friction-type high-strength bolted connections (FHBCs) was developed to connect steel frames to the infilled cross-laminated timber (CLT) shear walls. In the FHBC, an opening was cut in the CLT near the wall-to-beam interface. Two predrilled holes existed within the CLT panel, running vertically from the bottom surface of the opening to the wall-to-beam interface. Two slotted holes were also predrilled on the top flange of the steel beam. Two high-strength bolts were attached to the upper anchor plate installed in the opening and the bottom anchor plate placed below the top flange of the steel beam. By applying the pretension force on the bolts, the CLT panel was pressed against the steel beam, forming the static friction force to resist the shear force along the wall-to-beam interface. In the study, cyclic tests were conducted to evaluate the friction properties of the interface between the infilled CLT wall and the steel beam. The CLT-steel friction coefficient was carefully investigated, which was a critical parameter for determining the maximum static friction force of the FHBCs. Three-dimensional solid finite element models were developed to predict the load-slip behaviors of the FHBCs, and their multi-stage load-slip behaviors were analyzed using the step-by-step method. It is found that the CLT-to-steel interface can perform with considerable shear-resisting capacity and shear stiffness in the pre-sliding friction as well as stable energy-dissipating capacity in its post-sliding behavior. The maximum static friction coefficient and the dynamic friction coefficient of the interface are recommended as 0.55 and 0.50, respectively. When the pretension force is enhanced from 40 kN to 80 kN, for the FHBCs with the three-layer CLT and those with the five-layer CLT, their ultimate shear-resisting capacity increases by 75.85% and 35.67%, respectively. The load-slip curves from the FHBC models exhibit a similar pre-sliding behavior with considerable shear stiffness and shear-resisting capacity. Whereas, the numerical load-slip curves of the post-sliding stage are distinctive between the FHBCs with the three-layer CLT and those with the five-layer CLT.

Modified Split Mandrel Method and Equipment to Improve the Fatigue Performance of Structural Components with Fastener Holes

Fastener holes are among the most common natural stress concentrators in metal structures. The life cycles of various structural elements, such as those in aircraft structures, automobiles, and rail-end bolt joints, are limited by fatigue damage around the holes. An effective approach to delay the formation and growth of fatigue macrocracks is to introduce residual hoop compressive stresses around the holes. Two methods have become established in the prestressing of fastener holes in aircraft components, split sleeve and split mandrel, which implement one-sided processes. The common disadvantage of both methods is the complex procedure due to the need for high accuracy of the initial holes. This article presents a new modified split mandrel method providing the same tightness (interference fit) with a wide tolerance of the pre-drilled hole diameters, reducing the number of technological cycle steps and production costs. To implement the new method, a functionally connected tool and a device with a hydraulic drive were developed. An extensive experimental study of 2024-T3 AA specimens was carried out to evaluate the effectiveness of the method under a high scattering of the pre-drilled holes. The new method provided a deep zone of residual hoop compressive stresses on both faces of the specimens after cold working and after hole final reaming. The removal of a plastically deformed layer around the hole of suitable thickness during the final reaming decreased the axial gradient of residual hoop stress distribution. Fatigue tests on a tensile pulsating cycle verified the effectiveness of the modified split mandrel method to significantly increase the fatigue life by 6.6 times based on 106 cycle fatigue strength compared to the conventional case of machining the holes. The obtained S-N curves for three groups of samples with initial hole diameters of 8.0, 8.1, and 8.2 mm, which were cold worked with the same tightness of 0.32 mm and final reamed, aligned well, indicating that the new method can provide constant fatigue strength for a given stress amplitude.

Influence of various pilot hole profiles on pedicle screw fixation strength in minimally invasive and traditional spinal surgery: a comparative biomechanical study.

Despite advancements in pedicle screw design and surgical techniques, the standard steps for inserting pedicle screws still need to follow a set of fixed procedures. The first step, known as establishing a pilot hole, also referred to as a pre-drilled hole, is crucial for ensuring screw insertion accuracy. In different surgical approaches, such as minimally invasive or traditional surgery, the method of creating pilot holes varies, resulting in different pilot hole profiles, including variations in size and shape. The aim of this study is to evaluate the biomechanical properties of different pilot hole profiles corresponding to various surgical approaches. Commercially available synthetic L4 vertebrae with a density of 0.16g/cc were utilized as substitutes for human bone. Four different pilot hole profiles were created using a 3.0mm cylindrical bone biopsy needle, 3.6mm cylindrical drill, 3.2-5.0mm conical drill, and 3.2-5.0mm conical curette for simulating various minimally invasive and traditional spinal surgeries. Two frequently employed screw shapes, namely, cylindrical and conical, were selected. Following specimen preparation, screw pullout tests were performed using a material test machine, and statistical analysis was applied to compare the mean maximal pullout strength of each configuration. Conical and cylindrical screws in these four pilot hole configurations showed similar trends, with the mean maximal pullout strength ranking from high to low as follows: 3.0mm cylindrical biopsy needle, 3.6mm cylindrical drill bit, 3.2-5.0mm conical curette, and 3.2-5.0mm conical drill bit. Conical screws generally exhibited a greater mean maximal pullout strength than cylindrical screws in three of the four different pilot hole configurations. In the groups with conical pilot holes, created with a 3.2-5.0mm drill bit and 3.2-5.0mm curette, both conical screws exhibited a greater mean maximal pullout strength than did cylindrical screws. The strength of this study lies in its comprehensive comparison of the impact of various pilot hole profiles commonly used in clinical procedures on screw fixation stability, a topic rarely reported in the literature. Our results demonstrated that pilot holes created for minimally invasive surgery using image-guided techniques exhibit superior pullout strength compared to those utilized in traditional surgery. Therefore, we recommend prioritizing minimally invasive surgery when screw implantation is anticipated to be difficult or there is a specific need for stronger screw fixation. When opting for traditional surgery, image-guided methods may help establish smaller pilot holes and increase screw fixation strength.

Study on the elastic stiffness calculation method of single-bolted steel-bamboo scrimber-steel shear connections

Bolted steel-bamboo scrimber-steel (SBSS) connections are commonly employed in composite bamboo structures, but their equivalent stiffness in the elastic phase is difficult to determine. This study develops a novel theoretical formula for estimating the equivalent stiffness in the elastic phase of single-bolted SBSS shear connections considering various failure modes. Specifically, the method focuses on calculating the contact stiffness between the bolt and the pre-drilled hole wall, as well as the shear load applied to the bolt end by the steel plate. The method uses the double-shear yield mode, which is included by European Yield Modes (EYM), and the beam on elastic foundation theory (BEFT), and considers the bamboo scrimber embedment stiffness, bolt diameter and steel plate strength class. The method is tested by conducting experiments on single-bolted SBSS connections with varying load and fiber direction (LFD) angles, bolt diameters, steel plate thicknesses and strength grades. The results show that the connection stiffness increases with bolt diameter and steel plate strength grade, decreases with LFD angle, and is not affected by steel plate thickness. The parameter μ, which is important in the theoretical equations, is also calibrated based on the experimental data. The proposed method is validated by comparing it with existing test results of single-bolted SBSS connections. This paper provides a simple and reliable model for predicting the equivalent stiffness in the elastic phase of bolted SBSS connections in bamboo scrimber structures and offers useful insights for their design.

Effect of Core Hole Diameter on Tensile and Fatigue Properties of the Helically Formed Internal Thread in AlSi10MnMg Cast Alloys

The manufacturing of internal thread using the helical thread forming process (Punch Tap) as a novel high-performance manufacturing technology provides high productivity by reducing the tool path, which can save manufacturing time up to 75% compared to the conventional thread forming process. For instance, cast gearboxes in the transport sector consisting of numerous internal threads can benefit from this manufacturing method to realize detachable joints. While the required core hole diameter for conventional (cut) tapping depends on the thread dimension, this diameter depends either on the material properties for the thread forming process. The proper core hole diameter according to material flow possibility enables forming of complete thread profiles, which can consequently enhance the mechanical properties of the thread. This study aims to analyze the effect of the core hole diameter on the quality of the formed threads in AlSi10MnMg cast profiles. M6 threads were formed into the pre-drilled core holes with two different diameters. CT-scan analysis indicated that reducing the core hole diameter decreases the inner volume of the formed internal thread, which is justified by better material flow and complete forming of the thread profiles. Adaptation of the manufacturing parameters according to the material properties enhanced the geometry of the formed thread profiles. This enhancement increased the tensile and fatigue strengths of the detachable joints by subjecting the four initially formed threads at the top of manufactured nuts to the static and cyclic loads.

Experimental study on crushing of concrete slabs by high-voltage pulse discharge

To investigate the effectiveness of high voltage pulse discharge (HVPD) in crushing concrete slabs, HVPD in-liquid tests were conducted in pre-drilled holes in three double-layer bi-directionally reinforced and twelve single-layer bi-directionally reinforced concrete slabs. The parameters that were varied in the tests included the concrete strength, discharge hole diameter and spacing, discharge voltage and number of copper wires discharged. The results showed that the explosion caused by HVPD using copper wires increased the crack width by more than 34.8% compared to that caused by the electrohydraulic effect. After 10 explosions caused by HVPD using copper wires, the single-layer reinforced concrete slab was split into several slabs by cracks to achieve the crushing effect. The single discharge energy, i.e., discharge voltage, had a significant effect on the crushing of concrete slabs, and the width of concrete cracks produced by a 100 kV discharge was more than twice that of a 40 kV discharge. The increase in concrete strength acted as a crack arrestor for the slabs, and the crack width of C20 concrete slabs increased by approximately 10% to 25% compared to C40 concrete slabs. The increase in crack width with increasing number of discharged copper wires decreased with increasing discharge voltage. The width of concrete cracks produced by the explosion of 60 copper wires compared to 30 copper wires increased by approximately 10% at 100 kV and by approximately 20% from 60 to 80 kV. The crack width of concrete slabs with discharge holes of diameter 40 mm increased by approximately 5% to 15% compared to concrete slabs with holes of 50 mm. Expressions for the relationships between the damage degree of the concrete slab (i.e., the width of the concrete cracks around the holes on the outside of the slab) and the key parameters such as the output voltage, the number of discharged copper wires, and the strength grade of the concrete were established based on the experimental results.

Behaviour of bonded-in dowel shear connections in timber lightweight concrete composite beams including effect of an interlayer

With the need of renovation in the current timber structures, use of a cement based layer is a popular solution, which improves the structural integrity and increases the structural mass. In this paper, the use of a lightweight concrete with dowel type connections is investigated since such a combination can serve for both new and existing structures. Two types of dowel connections are experimentally tested, screws and bonded-in rods, to observe their limits and the contribution of an adhesive. To extend the application to an existing structure where a wood-based flooring may be present (such as OSB), which acts as an interlayer in the composite solution, the connections are tested with an interlayer as well. To overcome this challenge, in this paper, the predrilled hole at the wood based material (timber and interlayer) is filled with an adhesive to form a bond to the connection. The experimental results indicate that the addition of an adhesive lead to a positive contribution in mechanical properties. The experimental results are compared with the analytical approaches given in the current codes. The difference in comparisons are justified and further supported with the literature.

Selective electrochemical boring of thin-walled tubes: Methodology, mechanism, and characteristics

Corrugated tubes having internally turbulated surface find intensive application in heat-exchangers. Fabrication of thin-walled tubes with turbulated internal surface using conventional machining processes is difficult due to the inability of tube wall to withstand the cutting force. With non-contact type machining processes, a methodology is yet to be developed for selective boring of thin walled tubes. In this research, we propose a novel approach to bore a thin-walled tube at selective locations using electrochemical route and the operation is termed as selective-electrochemical boring (SECB). Machining centre is fabricated in-lab and experiments are carried out using a partially-insulated single-point tool. Experiments are performed to study the influence of process parameters on different characteristic features of a groove profile. With the developed machining centre and the proposed machining methodology, multiple internal grooves with sub-micron level surface roughness are fabricated and subsequently characterized. Minimum surface roughness (Ra) of 0.064 μm is achieved inside the groove on SS-304 tube. The unique feature of this invention is its ability to machine internal as well as external grooves at the selected location without the need for a specifically-shaped tool. Application of the proposed methodology can be extended to machining of turbulated profile on pre-drilled holes in turbine blades for enhancing heat transfer rate.

Mechanical joining of sheets to tubes by a sheet bending-unbending cycle

The utilization of an axial sheet bending-unbending cycle was previously utilized to produce mechanical joints of sheets to rods at ambient temperature by two subsequent operations. In this research, that joining process is now extended to produce a hidden mechanical joint between a sheet and tube that may not have protrusions both at the sheet surface and at the inner tube wall (if a mandrel is inserted there during the joining operation). The process is performed at ambient temperature and starts with the axial bending of a sheet with a pre-drilled hole of smaller diameter than that of the external diameter of the tube. That hole will be enlarged until a point where its diameter matches the external diameter of the tube to allow for its insertion. In a following operation, the sheet is unbent back to its original form, which will force the sheet material near the adjacent region of the hole to flow into a circular slot previously machined in the tube.Although the joining process is successful, the feasibility of the first axial sheet bending operation can be compromised, since it relies on a predetermined vertical displacement to ensure that its pre-drilled centre hole has the same diameter as the external diameter of the tube or rod that is to be inserted inside that hole, so that the mechanical joint is produced after the unbending of the sheet. To address those limitations, a modification is also proposed to the joining process where a redesigned punch tool allows to calibrate the hole diameter and guarantee that the tube or rod can be inserted correctly inside that hole for every joint to be produced while keeping tight tolerances.The combination of numerical modelling and experimentation allowed to determine the working parameters and their respective influence in the overall mechanics of the process. Unit test cells were utilized to prove the feasibility of the new concept and evaluate its pull-out destructive performance, although the joining process can easily be extended to larger tube and sheet dimensions since the plastic deformation is localized.

Application status of open-wedge high tibial osteotomy assisted by three-dimensional printing patient-specific cutting guides

To review the application of three-dimensional (3D) printing patient-specific cutting guides (PSCG) in open-wedge high tibial osteotomy (OWHTO). The domestic and foreign literature about the use of 3D printing PSCG to assist the OWHTO in recent years was reviewed, and the effectiveness of different types of 3D printing PSCG to assist OWHTO was summarized. Many scholars design and use different 3D printing PSCGs to confirm the precise positioning of the osteotomy site (the bone surface around the cutting line, the "H" point of the proximal tibia, the internal and external malleolus fixators, etc.) and the correction angle (the pre-drilled holes, the wedge-shaped filling blocks, the angle-guided connecting rod, etc.) during operation, and all of them achieve good effectiveness. Compared with conventional OWHTO, 3D printing PSCG assisted OWHTO has many obvious advantages, such as shortening the operation time, and the frequency of fluoroscopy, and being closer to the expected preoperative correction, etc. However, the effectiveness between different 3D printing PSCGs still need to be discussed in the follow-up studies.

Effects of Velocity Profile and Plate Usage on Identified Bone Strength during Instrumented Screw Insertion

Bone screws are important in orthopaedic surgery to treat fractures and secure implants. Over- or under-tightening these screws may lead to premature failure of the screw fixation, necessitating risky and costly revision surgery. Previously, a model-based method for automatically optimising bone screw insertion torque was developed. This paper expands on the prior testing of this method, to investigate how non-ideal conditions may affect the model accuracy/precision.A bone screw was inserted into pre-drilled holes in artificial bone made from PU foam. Three cases were tested: first the screw was inserted directly with a constant velocity, then it was inserted with a trapezoidal velocity profile, and lastly it was inserted with a constant velocity profile, but through a hole in a metal plate. Each case was repeated 20 times for 60 total insertions. Torque and angular displacement measurements were used with a previously-developed model to identify the foam material strength for each insertion. Summary statistics were calculated for each case and statistical tests were used to compare the means and variances for the identified values between each case.Comparing to base base case with constant velocity and no plate: we found a statistically significant (p < 0.05) difference in the mean identified strength for the trapezoidal velocity and the case with the plate. We found a statistically significant difference in the variance for the trapezoidal velocity profile (p < 0.05), but not for case with the plate present (p = 0.16).Future work should investigate these effects over a wider range of materials and screws.

Hidden mechanical joints of sheets to rods by axial sheet bending and unbending

Mechanical joints of sheets to rods by plastic deformation produced at room temperature away from the rod ends have been investigated in recent years but new developments are still needed. The process hereby presented relies in the axial bending of a sheet with a pre-drilled hole of smaller diameter than that of the rod, until the diameter of the sheet becomes equal to the initial diameter of the rod. Then, a rod is placed inside this larger hole diameter of the sheet and the sheet is unbent to its original shape, with its material being radially injected to a rectangular cross-section slot previously machined in the rod, thus producing a mechanical interlocking between the two geometries. The major process parameters are identified and their influence in the deformation mechanics is analysed by means of finite element modelling and experimentation. The experiments were carried out in unit cells while the numerical modelling analysed sheets of different lengths and thicknesses, so that to allow a proper understanding of the influence of different specifications on the new joining by forming process. Destructive performance tests were performed in the sheet-rod connections and comparisons with previous joining techniques were made to confirm the success of the new mechanical joint.

Assessing the efficacy of non-destructive testing methods to detect pitting corrosion

ABSTRACT Calibration of the non-destructive testing (NDT) methods for pipeline inspections is commonly done via machined defects with simple shapes and known sizes. However, such defects do not represent, e.g. an actual pit morphology observed in the field, which could lead to the unreliable interpretation of the inspection results. This work proposed a systematic approach to create and characterise real pits in stainless steel pipe specimens to assess the sensitivity of selected NDT methods. Pipe samples with three different diameters and thicknesses were used. Pits of different geometries and dimensions were generated by electrochemical methods, and immersion in an acidic ferric chloride solution filled in pre-drilled holes on the external surface of the specimens. NDT methods including radiography, Eddy current and dye penetrant testing were used for detecting and sizing the pits. The results were then compared with true pit depths obtained from cross-section analysis. Radiography and Eddy current methods failed to detect small pits with depths less than 70 µm. The porous metal cover on the pit mouth affected the detectability of radiography, while it had little impact on Eddy current testing. The findings of this investigation could be used to design training and calibration blocks for NDT methods.

Mechanical behavior of rotary friction welding joints composed of laminated veneer bamboo substrate and bamboo dowel

Rotary friction welding is a new connecting technique to produce joints by melting and re-solidification processes of substances, which has been pioneered in wooden furniture and structures due to the high interface strength. Bamboo has similar chemical components to wood and is a practical supplement to timber for applications. In this regard, the bamboo dowel was explored in this work to connect laminated veneer bamboo substrates using the rotary friction welding technique. The bond strength and shear strength of the proposed joints were experimentally evaluated by pull-out tests and single-shear tests based on the orthogonal array testing methodology. The effects of pre-drilled hole diameter, rotation rate, welding angle and substrate thickness on the mechanical behavior were investigated. The failure modes and load-carrying capacity were analyzed and discussed. Two failure modes including the pull-out failure and dowel fractured failure in pull-out tests and three failure modes including the pull-out failure, shear failure and hybrid failure of dowels in single-shear tests, were observed. It was found that the bond strength and shear strength of joints were primarily influenced by the pre-drilled hole diameter and the welding angle, respectively. The maximum bond strength of 4.40 MPa and maximum shear strength of 4.24 kN were achieved with the pre-drilled hole diameter of 8 mm and the welding angle of 45°, respectively. Furthermore, the results of scanning electron microscope observation and Fourier transform infrared spectroscopy analysis indicated that the bamboo fibers wound on the dowel surface and the relative contents of lignin increased. The research would provide the theoretical and technical basis for the application of bamboo rotary friction welding.

Influence of pre-drilling hole and feed rate on welded surface strength of pine-itauba joints

Rotary friction welding technique is a promising alternative of joining dowel-laminated timber (DLT) and dowelled cross-laminated timber (DCLT), without any adhesive. Studies on the welding of Brazilian woods are few and recent, mainly when determining the optimal welding parameters. Therefore, an exploratory study was carried out to evaluate the influence of pre-drilling hole and dowel feed rate on the welded surface strength of pine (Pinus taeda) and itauba (Mezilaurus itauba) joints, determining optimal welding parameters for these woods. The study was complemented with a macrostructural analysis of welded specimens and the determination of the taper rate of itauba dowels, to comprehend the mechanical performance of these welded joints. The specimens comprised itauba dowels, 10 mm in diameter, welded at a rotation of 1000 rpm and feed rates of 100, 300, 400 and 500 mm/min, into single-stage (8 mm in diameter) and two-stage (8 and 7 mm in diameter) pre-drilled holes, made in pine substrates. They were subjected to tensile tests and to macrostructure analysis. The results revealed that two-stage pre-drilled holes contributed to improving the mechanical strength of these welded joints. Feed rates higher than 100 mm/min avoid excessive wear and charring of the dowels, while feed rates lower than 500 mm/min prevent dowel splintering. The optimal welding parameters for pine joints welded with itauba dowels are two-stage pre-drilled holes and a feed rate of 400 mm/min.