Experimental investigation on the effect of accelerated ageing conditions on the pull-out capacity of compressed wood and hardwood dowel type fasteners

Holzforschung ◽  
2021 ◽  
Vol 0 (0) ◽  
Author(s):  
Sameer Mehra ◽  
Annette M. Harte ◽  
Adeayo Sotayo ◽  
Zhongwei Guan ◽  
Conan O’Ceallaigh
Keyword(s):  
Shape Recovery ◽  
Mechanical Performance ◽  
Accelerated Ageing ◽  
Recovery Effect ◽  
Climate Conditions ◽  
Robotic Fabrication ◽  
Pull Out ◽  
Timber Construction ◽  
Timber Connections ◽  
Compressed Wood

Abstract The widespread use of adhesives in timber construction has negative implications for the end-of-life disposal or re-use of the structural timber components. To promote the circular bioeconomy, it is preferable to substitute adhesives with more sustainable alternatives such as wood-based connectors. Today, robotic fabrication technologies facilitate the development of dowel-laminated timber (DLT) products whereby hardwood dowels are used to connect timber laminates as a substitute to adhesives. In recent years, thermo-mechanical densification of wood has resulted in significant improvements in the mechanical performance of the wood. This modified product often termed compressed wood (CW) has a shape-recovery effect which may be beneficial for the development of DLT products and timber-timber connections with improved friction fit with time. To test the hypothesis, accelerated ageing tests were carried out on CW-timber and hardwood-timber dowel type connections subjected to variable climate conditions. Finally, the capacity of the connections or friction fit was assessed using pull-out tests. Results show that the shape-recovery effect leads to the continuous expansion of the CW dowels and facilitates a friction fit with the timber substrate yielding higher pull-out loads when compared to hardwood dowels.

scholarly journals Microstructure and Mechanical Performance of Resistance Spot Welded Martensitic Advanced High Strength Steel

Processes ◽  
2021 ◽  
Vol 9 (6) ◽  
pp. 1021
Author(s):  
Yunzhao Li ◽  
Huaping Tang ◽  
Ruilin Lai
Keyword(s):  
Mechanical Properties ◽  
Failure Modes ◽  
Mechanical Performance ◽  
Strong Dependence ◽  
High Strength ◽  
Weld Nugget ◽  
Resistance Spot ◽  
Pull Out ◽  
Cross Tension ◽  
Spot Welded

Resistance spot welded 1.2 mm (t)-thick 1400 MPa martensitic steel (MS1400) samples are fabricated and their microstructure, mechanical properties are investigated thoroughly. The mechanical performance and failure modes exhibit a strong dependence on weld-nugget size. The pull-out failure mode for MS1400 steel resistance spot welds does not follow the conventional weld-nugget size recommendation criteria of 4t0.5. Significant softening was observed due to dual phase microstructure of ferrite and martensite in the inter-critical heat affected zone (HAZ) and tempered martensite (TM) structure in sub-critical HAZ. However, the upper-critical HAZ exhibits obvious higher hardness than the nugget zone (NZ). In addition, the mechanical properties show that the cross-tension strength (CTS) is about one quarter of the tension-shear strength (TSS) of MS1400 weld joints, whilst the absorbed energy of cross-tension and tension-shear are almost identical.

scholarly journals Impact of Prolonged Exposure of Eleven Years to Hot Seawater on the Degradation of a Thermoset Composite

Polymers ◽  
2021 ◽  
Vol 13 (13) ◽  
pp. 2154
Author(s):  
Amir Hussain Idrisi ◽  
Abdel-Hamid I. Mourad ◽  
Muhammad M. Sherif
Keyword(s):  
Exposure Time ◽  
Prolonged Exposure ◽  
Mechanical Performance ◽  
Matrix Cracking ◽  
Pull Out ◽  
Strength Based ◽  
Different Temperatures ◽  
River Line ◽  
Composite Samples

This paper presents a long-term experimental investigation of E-glass/epoxy composites’ durability exposed to seawater at different temperatures. The thermoset composite samples were exposed to 23 °C, 45 °C and 65 °C seawater for a prolonged exposure time of 11 years. The mechanical performance as a function of exposure time was evaluated and a strength-based technique was used to assess the durability of the composites. The experimental results revealed that the tensile strength of E-glass/epoxy composite was reduced by 8.2%, 29.7%, and 54.4% after immersion in seawater for 11 years at 23 °C, 45 °C, and 65 °C, respectively. The prolonged immersion in seawater resulted in the plasticization and swelling in the composite. This accelerated the rate of debonding between the fibers and matrix. The failure analysis was conducted to investigate the failure mode of the samples. SEM micrographs illustrated a correlation between the fiber/matrix debonding, potholing, fiber pull-out, river line marks and matrix cracking with deterioration in the tensile characteristics of the thermoset composite.

Predictions of the Mechanical Performance of Leaf Fiber Thermoplastic Composites by FEA

2021 ◽  
Author(s):  
Faris M. AL-Oqla
Keyword(s):  
Composite Materials ◽  
Cantilever Beam ◽  
Mechanical Performance ◽  
Natural Fiber ◽  
Fiber Composite ◽  
Fiber Composites ◽  
Fiber Types ◽  
Natural Fiber Composites ◽  
Pull Out ◽  
Structural Applications

The available potential plant waste could be worthy material to strengthen polymers to make sustainable products and structural components. Therefore, modeling the natural fiber polymeric-based composites is currently required to reveal the mechanical performance of such polymeric green composites for various green products. This work numerically investigates the effect of various fiber types, fiber loading, and reinforcement conditions with different polymer matrices towards predicting the mechanical performance of such natural fiber composites. Cantilever beam and compression schemes were considered as two different mechanical loading conditions for structural applications of such composite materials. Finite element analysis was conducted to modeling the natural fiber composite materials. The interaction between the fibers and the matrices was considered as an interfacial friction force and was determined from experimental work by the pull out technique for each polymer and fiber type. Both polypropylene and polyethylene were considered as composite matrices. Olive and lemon leaf fibers were considered as reinforcements. Results have revealed that the deflection resistance of the natural fiber composites in cantilever beam was enhanced for several reinforcement conditions. The fiber reinforcement was capable of enhancing the mechanical performance of the polymers and was the best in case of 20 wt.% polypropylene/lemon composites due to better stress transfer within the composite. However, the 40 wt.% case was the worst in enhancing the mechanical performance in both cantilever beam and compression cases. The 30 wt.% of polyethylene/olive fiber was the best in reducing the deflection of the cantilever beam case. The prediction of mechanical performance of natural fiber composites via proper numerical analysis would enhance the process of selecting the appropriate polymer and fiber types. It can contribute finding the proper reinforcement conditions to enhance the mechanical performance of the natural fiber composites to expand their reliable implementations in more industrial applications.

scholarly journals Finding the Key: Designing Timber Connections for CLT Panels

2021 ◽  
Author(s):  
◽  
Gabriella Joyce
Keyword(s):  
Large Scale ◽  
Computational Design ◽  
Digital Fabrication ◽  
Timber Construction ◽  
Structural Capacity ◽  
Connection System ◽  
Digital Modelling ◽  
Thermal Bridging ◽  
Timber Connections ◽  
Mass Timber

<p>In a climate where standard methods of construction are being challenged, developments in engineered timbers are allowing mass timber construction to be explored as a sustainable alternative to traditional building methods. Cross- laminated timber (CLT) is at the forefront of this evolution and, with the advancement in computational design and digital fabrication tools, there lies an opportunity to redefine standard construction. This project explores how digital modelling and advance digital fabrication can be combined to generate a connection system for CLT panels.  The advantages of CLT and mass timber construction are numerous and range from environmental and aesthetic benefits to site safety and cost reduction benefits. There are, however, issues that remain surrounding the connections between CLT panels. Steurer (2006, p.136) stated that, “Progress in engineered timber construction is directly related to developments in connector technology.” This thesis creates connections inspired by traditional Japanese joinery that have been adapted to be used for the panel construction of CLT structures. Using CLT offcuts as a primary connection material, the system not only reduces waste but also mitigates thermal bridging and lowers the number of connection points whilst increasing the ease of building and fabrication.  The connections are first considered at a detail scale. They use the literature review and case studies as a base for design before being tested using digitally fabricated prototypes. These prototypes are evaluated against a framework created in line with the aforementioned criteria. Within this framework, the connections are analysed against existing connection systems as well as previous designs to establish a successful system. The connections are then evaluated within the context of a building scale and considers large-scale fabrication and on- site assembly whilst continuing to focus on the reduction of waste. This research found that the simplicity of the connections is key to a successful system as this allows for faster and cheaper fabrication and installation. However, there is still further research needed surrounding large-scale fabrication and the structural capacity of timber connection systems.</p>

Improvement of glued-in-rod joint system using compressed wooden dowel

Holzforschung ◽  
2010 ◽  
Vol 64 (6) ◽  
Author(s):  
Kiho Jung ◽  
Satoru Murakami ◽  
Akihisa Kitamori ◽  
Wen-Shao Chang ◽  
Kohei Komatsu
Keyword(s):  
High Performance ◽  
Base Material ◽  
Shear Tests ◽  
Joint System ◽  
Bonding Performance ◽  
Pull Out ◽  
Wooden Dowel ◽  
Application Potential ◽  
Compressed Wood ◽  
Insertion Length

Abstract The purpose of this study was to develop eco-friendly and high-performance glued-in-rod (GIR) joints using compressed wood (CW), which has higher tensile strength than normal hardwood, instead of conventional wooden dowels. To explore the bonding performance of the dowel and base material, punching shear tests were performed and relationships were established between the density of CW dowel and punching characteristics. Pull-out tests of GIR joints were performed and results were compared with those derived from a mechanical model to evaluate the influence of insertion length of dowel and to define its optimized length. The results indicate that CW dowel has almost the same bonding performance in the density range 330–1000 kg m-3. Hence, CW as a dowel material in GIR joints has a high application potential. Pull-out tests of GIR joints showed that the insertion length of dowel in GIR joints with the CW-67 dowel is the best if the length is 10 times larger than its diameter. In addition to its satisfactory bonding performance, CW dowels have excellent tensile characteristics.

Augmented drawn construction symbols: A method for ad hoc robotic fabrication

2020 ◽  
Vol 18 (3) ◽  
pp. 254-269
Author(s):  
Jens Pedersen ◽  
Narendrakrishnan Neythalath ◽  
Jay Hesslink ◽  
Asbjørn Søndergaard ◽  
Dagmar Reinhardt
Keyword(s):  
Construction Industry ◽  
Ad Hoc ◽  
Digital Fabrication ◽  
Manual Labor ◽  
Robotic Fabrication ◽  
Timber Construction ◽  
Digital Production ◽  
Global Construction ◽  
Human Interpretation ◽  
High Level

The global construction industry is one the least productive sectors over a 30-year period, which arguably could be related to virtually no implementation of digital and automation technologies within the construction industry. Construction processes arguably consist of expensive manual labor or manual operation of mechanized processes, where hand-drawn markings on work-objects or partly build structures are used to inform and steer the construction process or allows for ad hoc adjustments of elements. As such, the use of on-object, hand-drawn information is considered integral to the modus operandi of a plurality of construction trades, where timber construction and carpentry are of special interest. In contrast, emerging methods of digital production in timber construction implicitly or explicitly seek to eliminate the interpretive component to the construction work, imposing a top-down paradigm of file-to-factory execution. While such systems offer a performance increase compared to manual labor, it is notoriously sensitive to construction tolerances and requires a high level of specialism to be operated, which could alienate craft-educated workers. This research argues that developing methods for digital production compatible with on-site human interpretation and adaptation can help overcome these challenges. In addition, these methods offer the opportunity to increase the robustness and versatility of digital fabrication in the context of the construction site. The article reports on a new method titled “augmented drawn construction symbols” that through a visual communication system converts on-object hand-drawn markings to CAD drawings and sends them to a robotic system. The process is demonstrated on a full-scale prototypical robot setup.

Preliminary Results of Stress Recovery of Constrained NiTi SMA Wire for Aerospace Applications

2010 ◽  
Vol 643 ◽  
pp. 15-18
Author(s):  
Júlio Cesar Santos ◽  
Antunes Andre Da Silva ◽  
Afonso Paulo Monteiro Pinheiro ◽  
Leonardo Kyo Kabayama ◽  
Odair Doná Rigo ◽  
...  
Keyword(s):  
Shape Recovery ◽  
Electrical Current ◽  
Recovery Stress ◽  
Wire Electrode ◽  
Recovery Effect ◽  
Ignition System ◽  
Gas Leakage ◽  
Aerospace Applications ◽  
Niti Sma ◽  
The Wire

The rocket propellant ignition system uses electro-explosive device actuated by wire electrode. Those wires are usually made by Fe-Ni based alloy with controlled thermal expansion inserted into a ceramic feed-through and are connected to thin resistive wire which is heated through the passage of an electrical current for propellant ignition. The contact between ceramic feed-through and wires should be reliable since sometimes it could fail. A novel alternative process is to use SMA wires taking into account the shape recovery effect constraining the wire inside the feed-through. The recovery stress of 326 MPa for 4% pre-strain should be enough to constrain the wire inside the feed-trough avoiding the gas leakage.

FBG Sensor Application for GFRP Soil Nailing Pull-Out Test

2013 ◽  
Vol 477-478 ◽  
pp. 539-542 ◽  
Author(s):  
Qing Ping Jin ◽  
Zu Jia Zheng ◽  
Bin Qiang Dou ◽  
Xue Wen Lei
Keyword(s):  
Precise Measurement ◽  
Mechanical Performance ◽  
Difficult Problem ◽  
Soil Nailing ◽  
Pull Out ◽  
Sensing Technology ◽  
Pulling Force ◽  
Two Stages ◽  
Bragg Grating Sensor ◽  
Force Data

The mechanical performance of GFRP soil nailing in the supporting structure is an important and difficult problem. By implanting the fiber bragg grating sensor (FBG) into GFRP soil nailing, pull-out tests were done on filed,and stress rules of soil nailing bar were determined.The more reasonable and effective force data of soil nailings were also gathered through FBG senor.Test results show that the tension of soil nailing gradually adds with external pulling force, the variation of tension is divided into two stages, the total pulling force is within 50kN, growing linearly with about 2.5% rate ,after that, its growth rate is approximately 50% to 60%. After the force exceed a certain value, the load is transmitted backward.FBG sensing technology overcomes the failure problem of traditional strain sensor,is a precise measurement method.

Seismic performance of connections in heavy timber construction

2002 ◽  
Vol 29 (3) ◽  
pp. 389-399 ◽  
Author(s):  
Marjan Popovski ◽  
Helmut G.L Prion ◽  
Erol Karacabeyli
Keyword(s):  
Seismic Performance ◽  
Slenderness Ratio ◽  
Braced Frames ◽  
Cyclic Tests ◽  
Bolted Connections ◽  
Seismic Behaviour ◽  
Design Load ◽  
Timber Construction ◽  
Timber Connections ◽  
Steel Bolts

Results from monotonic and quasi-static cyclic tests on connections used in heavy timber construction are presented for two types of fasteners: steel bolts and glulam rivets. Bolted connections with three different diameter bolts, arranged in several configurations, as well as two different configurations of glulam rivet connections were tested. All configurations included a main glulam member and two steel side plates. For bolted connections, the seismic behaviour was found to be primarily dependent on the bolt slenderness ratio. Bolted connections with higher slenderness ratios (smaller diameter bolts) exhibited more ductile behaviour with considerable steel yielding and wood crushing before failure. Glulam riveted connections, which were designed in rivet failure mode, showed superior seismic performance when compared to bolted connections for similar design load levels. Riveted connections were also able to dissipate the highest amount of input energy before the failure was reached.Key words: timber connections, glulam rivets, bolts, ductility, timber, wood, braced frames, seismic performance, heavy timber construction.

Bond Behavior of FRCM Carbon Yarns Embedded in a Cementitious Matrix: Experimental and Numerical Results

2017 ◽  
Vol 747 ◽  
pp. 305-312 ◽  
Author(s):  
Jacopo Donnini ◽  
Giovanni Lancioni ◽  
Tiziano Bellezze ◽  
Valeria Corinaldesi
Keyword(s):  
Mechanical Performance ◽  
Stress Transfer ◽  
Polymer Coatings ◽  
Energy Functional ◽  
Numerical Results ◽  
Variational Model ◽  
Experimental Session ◽  
Cementitious Matrix ◽  
Pull Out ◽  
Multifilament Yarns

The use of inorganic cement based composite systems, known as Fiber Reinforced Cementitious Matrix (FRCM), is a very promising technique for retrofitting and strengthening the existing masonry or concrete structures. The effectiveness of FRCM systems is strongly related to the interface bond between inorganic matrix and fabric reinforcement, and, since the major weakness is often located on this interface, the study of stress-transfer mechanisms between fibers and matrix becomes of fundamental importance.FRCM are usually reinforced with uni-directional or bi-directional fabrics consisting of multifilament yarns made of carbon, glass, basalt or PBO fibers, disposed along two orthogonal directions. The difficulty of the mortar to penetrate within the filaments that constitute the fabric yarns and the consequent non-homogeneous stress distribution through the yarn cross section makes difficult to access the characterization of the composite material. The use of polymer coatings on the fibers surface showed to enhance the bond strength of the interface between fibers and mortar and, as a consequence, to improve the mechanical performance of the composite. The coating does not allow the mortar to penetrate within the filaments while is able to improve the bond between the two materials and to increase the shear stress transfer capacity at the interface.An experimental session of several pull out tests on carbon yarns embedded in a cementitious matrix was carried out. Different embedded lengths have been analyzed, equal to 20, 30 and 50 mm. The carbon yarns object of this study were pre-impregnated with a flexible epoxy resin enhanced with a thin layer of quartz sand applied on the surface.A variational model was proposed to evaluate the pull-out behaviour and failure mechanisms of the system and to compare numerical results to the experimental outcomes. Evolution of fracture in the yarn-matrix system is determined by solving an incremental energy minimization problem, acting on an energy functional which account for brittle failure of matrix and yarn, and for debonding at the yarn-matrix interface. The model was able to accurately describe the three phases of the pull-out mechanism, depending on the embedded length.

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