Block Shear Tests Research Articles

Influence of Laminate Twist and Clamping Pressure on Bonding Performance of Low-Grade Lumber in Cross-Laminated Timber

Abstract The geometric variations of low-grade lumber raise concerns about bond strength of cross-laminated timber (CLT) produced from such lumber. This study seeks to investigate the effect of low clamping pressure and geometric variations of laminates on the bond strength of CLT. CLT panels were manufactured from low-grade grand fir (Abies grandis). Block shear tests and cyclic delamination tests were conducted on specimens randomly taken at specific points that correspond to a wide range of twist magnitude. Twist distribution in the lumber used as laminates in the CLT ranges from 0 to 160 mm. Results showed that twist magnitude and clamping pressure have significant effect on bond performance, with twist magnitude having an overriding effect on pressure.

Fabrication of glass to PLA joints with an intermediate aluminum layer by using low-cost industrial nanosecond IR fiber lasers

We present an adhesive free, low-cost and effective solution for joining of thermoplastic additive manufactured parts to glass using an industrial nanosecond IR pulsed fiber laser. We demonstrate the potential of the method by means of laser joints of glass to Polylactic Acid (PLA). The glass to PLA joints are realized via Laser Transmission Welding (LTW) and Laser Direct Welding (LDW) using an intermediate sacrificial thin layer of aluminum. The laser joints are compared with adhesive glass to PLA joints. The mechanical testing involves a thorough strength evaluation by using block shear test method, demonstrating the superior performance of laser-welded joints over conventional adhesive alternatives. The results of these shear tests reveal a remarkable 565 % improvement in shear strength in comparison to the adhesive joints (maximum shear strength of laser bonds: 9.57 MPa). Furthermore, a Weibull statistical analysis is applied to assess the reliability of the joints, disclosing a very high survival probability of the samples under a loading of 4.5 MPa as well as a σ0 (stress for which the 1/e (37 %) of the samples survive) of 8.15 MPa.

Manufacturing Study on Different Glue Spread and Press Pressure for Glued Laminated Timber Made from Laran

Amidst challenges such as dwindling timber log supply from natural forests, concerns about timber quality, and rising timber costs, the timber industry has increasingly turned to engineered lumber solutions, including glued laminated timber (glulam) crafted from fast-growing species. However, the performance of glulam derived from plantation trees, notably swift-growing varieties like Laran, remains an area warranting exploration. This study addresses critical aspects of glulam production, encompassing adhesive selection, spread rate, and press pressure, which collectively influence material performance. The objectives of this research encompass an assessment of the bonding integrity of glulam originating from Laran plantation species and an evaluation of the optimal adhesive spread rate and press pressure for Laran-derived glulam. Various adhesive spread rates (200 g/m2, 250 g/m2, 350 g/m2 and 400 g/m2) and press pressures (0.7, 1.0 and 1.4 MPa), utilizing Phenol-Resorcinol Formaldehyde (PRF) adhesives, were systematically investigated in alignment with the guidelines stipulated in MS 758: 2020. Bonding integrity was evaluated via block shear and cyclic delamination tests. The study reveals that these parameters indeed exert a tangible influence on the bonding efficacy of PRF adhesive with Laran species. Remarkably, an optimal adhesive spread rate of 399.78 g/m2 and press pressure of 1.18 MPa emerged as pivotal thresholds for superior bonding outcomes. Notably, the significance of adeptly designed glulam beams within wooden structural frameworks is underscored, particularly in light of the multifaceted imperatives of sustainability, economics, and environmental conscientiousness.

Erratum to: Bonding Strength between Cross Layers of CLT Evaluated by Torsion and Compression Block Shear Tests [Mokuzai Gakkaishi Vol.67 (2021) No.2 p.100-108

Erratum to: Bonding Strength between Cross Layers of CLT Evaluated by Torsion and Compression Block Shear Tests [Mokuzai Gakkaishi Vol.67 (2021) No.2 p.100-108

Mechanical Properties of Laminated Veneer Lumber (LVL) Fabricated from Three Malaysian Hardwood Species

Theapplication of laminated veneer lumber (LVL) has long been limited to non-structural elements in Malaysia.LVL is commonly fabricated with veneer from low to medium density (290 to 630 kg/m3)softwood or temperate hardwood. The data on the properties of LVL made from medium to high density (567 to 687 kg/m3)tropical hardwood species is very limited. Therefore, this study investigated the mechanical properties of LVL fabricated from Malaysian hardwood species namely Kasai (Pometiaspp.), Mengkulang (Heritieraspp.) and Kedondong (Canariumspp.). Different variables were studied: i) wood species; ii) loading direction (flatwise or edgewise), iii) grain direction (parallel and perpendicular), iv) treatment condition. The bending and compression test was carried out in accordance with EN 408:2012, while the block shear test was conducted based on EN14374:2004 and EN 314-1:2004.The results show that the grain direction has the most significant effect (P≤ 0.01)on bending, compressive and bonding properties of the samples tested. The treatment conditions for block shear test also displayed significant effect on its shear strength. The samples loaded parallelly displayed 320-450% higher bending valuesthan the samples loaded perpendicularly. The compressive strength and compressive modulus were 323-365% and 523-2530% higher respectively when loaded parallelly.LVL performed the best mechanically when loaded parallelly and when subjected to Treatment A which was the least extreme treatment condition.

Pressure mapping and susceptibility to bonding failure for low-quality lamstock in cross laminated timber

Cross Laminated Timber (CLT) is thriving as a wood engineered material across the globe. As demand increases, lamstock solutions become necessary to supply the demand, and low-quality lumber has been pointed as an option to solve this problem. Nevertheless, low-quality lumber has significant warping that spreads skepticism towards bonding failure due to out-of-plane defects. This article aims to investigate bonding failure using a pressure mapping, built with a Pressure Prediction Model, comparing theoretical results with block shear and cyclic delamination tests observations. Block shear test indicates no significant difference of wood failure results among different pressures zones using 2-ply lamination samples with a manufacturing press of 414 kPa. Cyclic delamination occurred in an insignificant frequency for samples in all pressure zones analyzed. In summary, for this study, the bonding strength could resist the residual stresses caused by warping experimentally. The findings of this investigation can encourage CLT manufacturers to utilize undervalued and low-grade materials such as small diameter timber (SDT) as a feedstock and contribute to the sustainability of CLT market growth.

Bonding performance of cross-laminated timber-bamboo composites

Bamboo is one of the most important renewable resources in China, leading to the development of bamboo products as well. Alternative applications of bamboo need to be developed in the field of construction, especially in cross-laminated timber (CLT) construction, due to better mechanical performance of bamboo and the increasing popularity of CLT construction in recent years. The bonding performance of cross-laminated timber-bamboo (CLTB) composites fabricated with Spruce-pine-fir (SPF) dimension lumber and bamboo scrimber boards was investigated here. L9 (34) orthogonal experiments with four factors (adhesive type, adhesive spreading rate, clamping pressure, and clamping time) and three levels were applied to evaluate their impacts on the bonding indicators of CLTB through block shear and delamination tests. Results showed that adhesive type had the most critical influence on the bonding performance. The optimal manufacturing parameters were adhesive of phenol resorcinol formaldehyde (PRF), adhesive spreading rate of 250 g/m2, clamping pressure of 1.0 MPa, and clamping time of 420 min, respectively. PRF adhesive yielded higher block shear strength, wood failure percentage, and lower rate of delamination than one-component polyurethane (PUR) and emulsion polymer isocyanate (EPI), especially under wet or boiling condition.

Effect of bio-inspired surface texture on the resistance of 3D-printed polycarbonate bonded joints

Surface preparation before adhesive bonding is crucial to improve the resistance and durability of the joint by altering the surface properties of the adherend. The purpose of surface treatment is to clean the surface from contaminants, activate the adherend surface and create an optimal surface structure to promote adhesion mechanisms. In that context, this work aims to investigate the influence of substrate surface texturing on the resistance of adhesive joints. Two bio-inspired surface textures were investigated, Fish scale (FS) and Tree frog (TF). Polycarbonate (PC) specimens with different surface patterns were manufactured using the fused deposition modelling process. Surface morphology, such as pattern dimension (shape and depth), surface roughness (Ra), and wettability, were used to characterise the substrates. The influence of these texture patterns on the shear strength of adhesively bonded joints was evaluated through the standardised block shear test method ASTM D4501-01. Moreover, the shear strength of the structured joints was compared to the results from bonding with polished surfaces (surfaces abraded with 80, 600 and 1000 grit paper), and with as-printed surfaces. The results revealed that the FS and TF surface textures enhanced the shear strength by 242% and 283% compared to the adhesive joints with polished surfaces. It was also shown that the variation in depth of the bio-inspired surface texture has no significant impact on the joint strength. Failure analysis demonstrated that the fracture mode of bonded joints with polished surfaces was the adhesive failure while mixed failure (cohesive and adhesive) characterises the as-printed, TF and FS surfaces. Worthy results are obtained rising the effectiveness of surface texture for the PC's bonded joints. Graphical Abstract [Formula: see text] This is a graphical representation of the abstract.

Effect of pressing parameters on dimensional stability and bonding performance of thermally compressed coconut wood

Previous research on thermally compressed (TC) coconut wood has shown potential for structural applications. However, its dimensional stability needed to be improved. This study aimed to improve the dimensional stability of TC coconut wood for further use in laminated products by using relatively high pressing temperatures to make it more hydrophobic. TC specimens with a target compression ratio of 55 % were manufactured from low-density (LD, 332 ± 25 kg/m3) wood, and TC specimens with a target compression ratio of 25 % were manufactured from medium-density (MD, 514 ± 28 kg/m3) wood. Two pressing temperatures (170 °C and 200 °C) and three pressing times (1 h, 2 h and 3 h) were applied. Chemical changes, dimensional stability, physical and mechanical properties, and bonding performance of the specimens were examined. Thermal degradation of the LD specimens was higher than that of the MD specimens. Differences in chemistry between the surface and the interior could explain bonding behavior. Pressing temperature had a greater impact on wood degradation than the pressing time. Dimensional stability could be achieved at 200 °C pressing temperature. Most physical and mechanical properties of the TC specimens had decreased due to thermal degradation. However, compressive strength parallel to the grain and modulus of elasticity were not affected at the chosen pressing parameters. Bonding performance determined by block shear tests was dependent on the original material, panel assembly, and the sanding process. Longitudinally laminated panels made from MD specimens with sanded surfaces provided the highest block shear strength.

The Dimensional Stability and Bonding Performance of Hybrid CLT Fabricated with Lumber and COSB

The differences of physical and mechanical properties of different laminations, such as softwood, hardwood or other structural composite lumber, in hybrid cross-laminated timber (HCLT), lead to their dimensional stability and bonding performance more complex than generic cross-laminated timber (CLT). In this paper, the spruce-pine-fir (SPF) dimension lumber and construction oriented strand board (COSB) were employed to fabricate HCLT. The effects of four configurations and three adhesives on the dimensional stability and bonding performance of CLT and HCLT were evaluated in term of the water absorption (WA), thickness swelling (TS), block shear strength (BSS), wood failure percentage (WFP) and rate of delamination (RD). The results showed that with the increase of the COSB laminations, the WA of HCLT specimens decreased, and the values of TS, BBS and WFP increased. The configuration had a significant influence on the dimensional stability, BBS and WFP of the specimen. The adhesive had a significant influence on the dimensional stability and some bonding performances of the specimen. The phenol resorcinol formaldehyde (PRF) specimens had the lowest average RD value compared with the one-component polyurethane (PUR) and emulsion polymer isocyanate (EPI) specimens. Failures were prone to occur in the middle of the thickness of COSB lamination during block shear and delamination tests. The outcome of this paper could help the engineering application of HLCT.

Cross-Laminated Timber and Glulam from Low-Density Paraserianthes falcataria: A Look into Densification and Shear Strength

The aim of this study was to investigate the shear performance of cross-laminated timber (CLT) and glulam made from densified Paraserianthes falcataria laminas. The densification process involved pre-treatment, compression with heat (105 °C, 6 MPa), and a cooling phase. CLT was manufactured from densified laminas of different thicknesses (24–60 mm), while glulam was produced from densified laminas that underwent pre-treatments of (1) pre-steaming (0–30 min) and (2) alkaline pre-treatment (sodium hydroxide (NaOH) concentrations: 0%–9%). Both CLT and glulam were cut into a pre-determined size before being subjected to a block shear test. The findings showed that the presence of pre-steaming (20 min) exhibited the highest shearing strength value. In contrast, alkaline pre-treatment reduced the shear performance of glulam. Here, 24 mm and 30 mm CLT were found to have the highest shearing strength among the parameters. Pre-steamed laminas showed better wettability, but no statistically significant correlation between the contact angle and shear strength of glulam. The densification process reduced the fiber pore areas of the laminas. The fiber pore areas with a shear strength of glulam, with or without alkaline pre-treatment, revealed a weak correlation. The correlation between fiber pore areas and the shear strength of CLT show no statistical significance. Here, 30 mm CLT with lowest moisture content and highest wood failure percentage exhibited a better bonding performance.

Bond Quality and Durability of Cross-Laminated Flattened Bamboo and Timber (CLBT)

To achieve value-added utilization of domestic bamboo and plantation wood resources, this study investigated the feasibility of using flattened bamboo and Chinese fir for manufacturing cross-laminated bamboo and timber (CLBT). Two types of adhesives, one-component polyurethane (PUR), and phenol resorcinol formaldehyde (PRF), and three applied pressure parameters (0.6, 0.8, and 1.0 MPa) were used to fabricate small CLBT panels (375 mm × 500 mm). In this study, block shear and delamination tests were conducted to examine the bond quality and durability of CLBT panels. The results showed that a significant difference in the bonding shear strength (BSS) in both directions. The bonding shear strength in the minor strength direction (BSSminor) was 1.81–3.45 times higher than the bonding shear strength in the major strength direction (BSSmajor). The adhesive type was the major factor affecting the bond quality and delamination, while the bonding pressure had no significant effect on the bond quality and delamination. Compared with PRF adhesives, CLBT specimens prepared from PUR had higher bonding shear strength (BSS) and wood failure percentage (WFP). However, the durability of delamination specimens prepared by PUR was not as good as layered specimens prepared by PRF.

Durability of epoxy and polyurethane bonded timber-hybrid FRP joints under hygrothermal and weathering conditions

This paper investigates the bond between laminated veneer lumber (LVL) and flax-glass hybrid fibre reinforced polymer (HFRP) with different fabric stacking sequences in the LVL-HFRP joints exposed to (1) room condition at the temperature of 20 °C and relative humidity (RH) of 57% (as reference condition), (2) hygrothermal condition (50 °C and 95% RH), and (3) weathering environment (a dry-wet-ultraviolet radiation cyclic condition). Epoxy (EP) and polyurethane (PUR) adhesives were used to manufacture the HFRP composites and bond them to the LVL as LVL-HFRP joints. The joints were tested under block shear tests to evaluate the bond behaviour. The LVL block shear specimens were also tested as the reference for the shear strength change of the LVL in the joints. Fourier transform infrared spectroscopy (FTIR) and differential scanning calorimetry (DSC) tests were conducted to study the influence of the hygrothermal and weathering conditions on the functional groups and the glass transition temperature (Tg) of the LVL-HFRP joints. After the hygrothermal and weathering exposures, the results showed that the Tg of the EP-based and PUR-based HFRP in the LVL-HFRP joints increased due to the post-curing and the arrangement of the disordered urea groups. The average shear strength values of the LVL-HFRP joints bonded with the EP adhesive decreased by 4.6–35.2% and the reduction of the shear strength of the LVL part in the joints accounted for the decreased shear strength at the joint level. The average shear strength values of the LVL-HFRP joints bonded with the PUR adhesive decreased by 27.9–57.0% and the reduction of the shear strength at the joint level was controlled by the glass fibre layer of the PUR-based HFRP, regardless of the fabric stacking sequence in the PUR-based HFRP.

Shear strength and hardness of two tropical wood species as function of heat treatment

The aim of this study was to evaluate the effect of heat treatment on surface roughness, shear strength and hardness of two tropical wood species, namely batai (Paraserainthes falcataria) and sesendok (Endospermum malaccensis). Samples were exposed to temperature levels of 120 ºC and 180 ºC for 3 h and 6 h. The surface quality of the control and heat-treated samples were determined using a stylus technique. Hardness and shear strength of the samples were evaluated using Janka hardness and block-shear test, respectively. The results reveal that the surface roughness of batai improved 3 % for 80-grit and 5 % for 180-grit samples while surface roughness of sesendok improved 7 % and 10 % for 80-grit and 180-grit, respectively by the increase of the heat temperature and prolonged durations. Analysis of variance (ANOVA) also revealed that most of the tested properties on the treated wood were significantly affected by the species, girt number and also temperature. In contrast to the untreated wood species, the heat-treated wood species exhibited lower values of shear strength and hardness. Overall, the hardness and shear of both species were adversely influenced by heat exposure.

Bonding Strength between Cross Layers of CLT Evaluated by Torsion and Compression Block Shear Tests

Bonding Strength between Cross Layers of CLT Evaluated by Torsion and Compression Block Shear Tests

Integrated experimental and numerical study on flexural properties of cross laminated timber made of low-value sugar maple lumber

The objective of this study is to examine the mechanical performance of cross laminated timber (CLT) panels made of low-value sugar maple under out of plane loads through mechanical tests and numerical simulation. The laminations were sorted into High and Low classes based on the measured modulus of elasticity (MOE). Two 3-layer sugar maple CLT layups as High-Low-High and Low-High-Low glued with resorcinol-based adhesive and one CLT layup of High-Low-High glued with melamine-based adhesive were prepared. Block shear, long-span bending (span-to-depth ratio of 33:1) and short-span bending (5.5:1) tests were conducted to evaluate the bonding, flexural and shear behavior of these low-value sugar maple CLTs. With a limited sample size, the lab-manufactured low-value sugar maple CLT provided a 50% to 80% higher MOE and at least two times higher MOR than CLT type E1 from APA/PRG 320. Similar MOE and MOR improvements were found by comparing CLT made with other species from literatures. The finite element simulation of bending tests was conducted with the orthogonal constitutive law and the progressive damage model based on the calibrated material properties parameters from lumber rating and references. The simulation results on each CLT panel type have a reasonable comparison with experimental test data. Therefore, these integrated experiment and simulation methods can provide detailed mechanical behaviors of the low-value sugar maple CLT, which can also be applied to other CLT species and layup.

Evaluation of Single-Lap and Block Shear Test Methods in Adhesively Bonded Composite Joints

Adhesive bonding is increasingly being used for composite structures, especially in aerospace and automotive industries. One common joint configuration used to test adhesive strength is the single-lap shear joint, which has been widely studied and shown to produce significant normal (peeling) stresses. When bonding composite structures, the normal stresses are capable of causing delamination before the adhesive bond fails, providing inconclusive engineering data regarding the bonding strength. An alternative test is the block shear joint, which uses a shorter sample geometry and a compressive-shear loading to reduce normal stresses. Analytical models proposed by Goland and Reissner and Hart-Smith are used to compare the edge-bending moment for the two joint configurations. The stress distributions along the bondline are also compared using finite element analysis. Experimental tests are conducted to evaluate these analyses and the failure modes of each configuration are recorded. Block shear samples demonstrate a joint strength over 100% higher than single-lap shear specimen bonded with the same adhesive material. The lower joint strength measured in single-lap shear is found to be potentially misleading due to delamination of the composite adherend.

Effect of ACQ treatment on surface quality and bonding performance of four Malaysian hardwoods and cross laminated timber (CLT)

The objective of this study is to determine the effects of alkaline copper quaternary (ACQ) treatment on the surface quality and bonding performance of four Malaysian hardwood species, namely batai, sesenduk, rubberwood and kedondong. The samples were impregnated with 2% ACQ preservatives and bonded with phenol-resorcinol–formaldehyde resin for cross laminated timber (CLT) fabrication. The changes in density and the retention of both ACQ and copper after the treatment were recorded. Surface roughness and wettability of both treated and untreated samples were measured. Block shear and delamination tests were performed to evaluate the bond-line strength of CLT. The study revealed that the average surface roughness (Ra) of each species increased significantly. Wettability of batai, sesenduk, rubberwood and kedondong was significantly higher than that of the untreated samples suggesting an improvement in surface wettability. For single-species CLT, treated rubberwood has the highest shear strength followed by kedondong, sesenduk and batai with values of 9.53 N/mm2, 6.00 N/mm2, 5.68 N/mm2 and 4.19 N/mm2, respectively. While for mixed-species CLT, the combination of ACQ-treated rubberwood-sesenduk-rubberwood has the highest block shear strength with a value of 8.05 N/mm2. No delamination was observed from all samples. ACQ treatment was found to not affect the block shear strength significantly. Therefore, ACQ preservatives can be used to produce CLT with good bonding performance.

Modified pendulum hammer in impact tests of adhesive, riveted and hybrid lap joints

This paper presents a modified pendulum hammer adapted to test the impact strength of lap joints. The impact tests of lap specimens exhibited greater repeatability in terms of the results, compared with the tests of block specimens (specimens used in Block Shear Test (ISO 9653)). The modified testing device also allowed for testing of rivet and hybrid rivet–adhesive joints. The comparative tests showed that the impact strength of the hybrid connections was greater than the sum of the impact strengths of the adhesive and rivet joints. Our research demonstrated the significant effect of the impact speed on the measured impact strength; this effect appeared to be related to the deformation energies of the test device and connected elements, which were more deformed at a lower load speed. We also showed a serious influence of adhesive forces on the impact strength of glued joints.

Examination of the block shear fracture test method to measure the Mode-II critical stress intensity factor

Block shear fracture tests were conducted using specimens of western hemlock to determine the properties of the fracture mechanics under the Mode-II condition. In the test, a fixture standardised as the block shear test of solid wood in the Japanese Industrial Association (JIS Z2101-2009) was used. The specimen configuration, location of the crack, and initial crack length were varied, and the effects of these conditions were examined. The Mode-II critical stress intensity factor was effectively obtained when the initial crack was introduced at the opposite location to that where the shear load was applied using a specimen with a cubic configuration. Additionally, the introduction of the additional crack length due to the fracture process zone ahead of the crack tip was also effective in the block shear fracture test and other Mode-II fracture tests.