Static Shear Strength Research Articles

Influences of low fines content and fines mixing ratio on the undrained static shear strength of sand–silt–clay mixtures

Clay and silt have complicated effects on the undrained behaviour of sands. To study the influences of low clay and silt contents on the undrained behaviour of sands in the clay–silt–sand mixtures, sands with three different fine contents (0%, 5% and 10%) and three different fines mixing ratios were investigated based on the consolidated-undrained test by a strain-controlled triaxial testing system. The test results show that the static liquefaction takes place in clean sands under static loading; the undrained behaviours of the specimens are found to differ for the same fine content and different fine mixing ratios. The fines can simultaneously influence filling, bonding and soil skeleton characteristics of sand particles, and the extent of the influence on each characteristic varies depending on the clay and silt contents.

Influence of Embedding Fiber Optical Sensors in CFRP Film Adhesive Joints on Bond Strength.

The increasing utilization of carbon fiber reinforced plastic (CFRP) in the aeronautical industry calls for a structural health monitoring (SHM) system for adhesively bonded CFRP joints. Optical glass fiber with inscribed fiber Bragg gratings (FBGs) is a promising technology for a SHM system. This paper investigates the intrusive effect of embedding optical glass fibers carrying FBGs on adhesive bond strength and adhesive layer thickness and quality. Embedding the optical glass fibers directly in the adhesive bond has the advantage of directly monitoring the targeted structure but poses the risk of significantly reducing the bond strength. Optical glass fibers with different cladding diameters (50, 80, 125 µm) and coating types (polyimide, with a thickness of 3−8 µm, and acrylate, with a thickness of ~35 µm) are embedded in structural and repair film adhesives here. Without embedded optical glass fibers, the film adhesives have an adhesive layer thickness of ~90 µm (structural) and ~100 µm (repair) after curing. The intrusive effect of the fiber embedding on the adhesive bond strength is investigated here with quasi static and fatigue single lap joint (SLJ) tensile shear tests. Also, the influence of hydrothermal aging procedures on the quasi static tensile shear strength is investigated. It is found that optical glass fibers with a total diameter (glass fiber cladding + coating) of ~145 µm significantly reduce the quasi static tensile shear strength and increase the adhesive layer thickness and number of air inclusions (or pores) in the structural film adhesive joints. In the repair adhesive joints, no significant reduction of quasi static tensile shear strength is caused by the embedding of any of the tested fiber types and diameters. However, an increase in the adhesive layer thickness is detected. In both adhesive films, no effect on the quasi-static tensile shear strength is detected when embedding optical glass fibers with total diameters <100 µm. The applied aging regime only affects the repair film adhesive joints, and the structural film adhesive joints show no significant reduction. A polyimide-coated 80 µm optical glass fiber is selected for fatigue SLJ tensile shear tests in combination with the more sensitive structural film adhesive. No significant differences between the S-N curves and tensile shear fatigue strength of the reference samples without embedded optical fibers and the samples carrying the polyimide-coated 80 µm optical glass fibers are detected. Thus, it is concluded that the influences of embedding optical glass fibers with total diameters <100 µm on the fatigue limit of the tested film adhesive joints is negligible.

Quasi-static and Dynamic Lap Shear Strength of Aluminium Joints Bonded with Epoxy/Alumina Nanocomposite Adhesive

Quasi-static shear strength of aluminium alloy single lap joints was determined as a function of wt% (0.5, 1.0, 1.5, and 2.0) of spherical and rod shaped nanoalumina in epoxy adhesive under compressive loading. Static shear strength for nanoadhesive containing 1.5 wt% of nanoparticles (for both spherical and rod shaped nanoalumina) was observed to be maximum. Dynamic shear strength for neat adhesive and nanoadhesives containing 1.5 wt% of spherical and rod shaped nanoalumina were analysed at two different loading rates using a split Hopkinson pressure bar system. A significant improvement (3 to 7 times) of dynamic shear strength of joints was perceived over static shear strength of joints. Static and dynamic lap shear strength for nanoadhesive containing nanospheres were significantly more than that for neat adhesive and nanoadhesive containing nanorods.

Influence of Kaolin content on the cyclic loading response of railway subgrade

Abstract Rail tracks passing through saturated subgrade soil often face a serious deterioration of bearing capacity and excessive deformation. One major reason is the excessive cyclic pore pressure that accumulates under the track that leads to soil softening and infiltration over the surface, i.e., subgrade mud pumping (fluidization). Although this issue has received considerable attention in recent decades, how the cyclic stress ratio and soil properties such as plasticity and void ratio influence the cyclic loading response of soft subgrade soil is still not properly understood. In this study, Kaolin – an artificial cohesive fines soil is used to modify a low plasticity subgrade soil to examine how the Kaolin content (cK) can affect its cyclic response. Soil specimens including the original soil and its mixture with 10 and 30% of Kaolin have been subjected to undrained cyclic testing. A cyclic stress ratio (CSR) varying from 0.2 to 1.2 is used and a low initial confining pressure of 20 kPa is applied. The results show 3 different responses of soil, i.e., (i) stable, (ii) cyclic undrained failure, and (iii) fluidization, depending on the magnitude of CSR. Where fluidization becomes imminent, the shear stress rapidly decreases at early stages. Adding cohesive fines, i.e., Kaolin reduces the static undrained shear strength and increases the plasticity index. This enables the test specimen to undergo a larger number of cycles (N) before failure, thus enhancing its resistance to fluidization. Specimens with a smaller initial void ratio, i.e., greater level of compaction, are less susceptible to fluidization because they can withstand larger CSR and N. Moreover, this study shows where there is potential fluidization upon cyclic loading, a significant redistribution of the water content seems to occur over the height of the test specimens.

Static bending of glulam beams manufactured with rubber wood and epoxy adhesive

The aim of this study was to evaluate the properties of Hevea brasiliensis wood wastes for production structural pieces of glued laminated (glulam) timber. Three trees with age close to 25 years and diameter at breast height (DBH) higher than 500 mm were obtained. The basic density of the wood were quantified, as well as the stiffness and the strength in static bending, shear strength and parallel compression to grain and hygroscopic equilibrium moisture. The beams of glulam were evaluated according to the modulus of elasticity (MOE), modulus of rupture (MOR) and delamination. Due to the bending properties MOR (75.14 MPa) and MOE (8166.79 MPa), as well as the shear strength (12.29 MPa) obtained, was concluded by the suitability of the rubber wood for the production of glulam beams. The composite beams presented values of MOR (75.14 MPa) and MOE (8166.79 MPa) compatible with species traditionally used in the production of glulam beams. The adhesive bond quality was verified by the delamination test, presenting delamination of 4.95 %, indicating its use for internal and external environments. Keywords: Composite; Wood; Bond resistance; Static bending.

Influential Factors of the Static Shear Properties of Coral Mud in the South China Sea

Coral mud, a kind of special material used for constructing islets in reclamation projects, is widely spread in the South China Sea. Combined with microstructure research, a series of triaxial tests were performed in this paper to study the static shear strength characteristics and potential factors that can influence them. The effective stress path was similar to the total stress path because of the unique microstructure resulting in a high strength and a high dissipation rate of the pore pressure in the coral mud. The initial void ratio and the initial confining pressure affected the strength and deformation characteristics of the coral mud. When the soil came to failure, the pore pressure coefficient Af varied linearly with the initial void ratio. The critical friction angle was greatly influenced by the confining pressure, and its magnitude first developed to a peak value and then decreased as the void ratio increased. This change showed that there was a linear relationship between the initial elastic modulus E0i and lgp0 as well as between the secant modulus E50 and p0. The estimation ability of Cam‐Clay was verified in this research. The value of parameter λ was determined incrementally by a larger initial void ratio, while the value of parameter M decreased smoothly first and then rose slightly; the selection of parameter κ was approximately 0.0035. The results supported that the Cam‐Clay model is able to simulate the stress‐strain relationship of coral mud, and a referenced estimation can be reliably and efficiently obtained for the reclamation projects of constructing islets.

Measuring the static shear strength of anaerobic adhesives in finite thickness under high pressure

ABSTRACT Although anaerobic adhesives are extensively used in addition to mechanical tightening in flanged couplings, interference fits, and threaded connections, their constitutive behaviour still needs to be investigated. According to the micromechanical model proposed by Dragoni and Mauri [Proc. of the IMECHE Part L J. of Mat.: Des. and Appl. 2002; 216: 9–15], the shear strength of the anaerobic adhesives significantly improves with the contact pressure applied to the thin adhesive layer. In order to assess this hypothesis, this work investigates the shear strength of an anaerobic adhesive layer with finite thickness and surface area, subject to a nearly-uniform contact pressure, up to 1000 MPa. The tests involved a head to head bonded specimen, made of high strength steel adherends (39NiCrMo3), with a controlled roughness on the bonding surfaces. Both a weak and a strong anaerobic adhesive (Loctite 243 and Loctite 638) are investigated. A full-field technique, such as the Digital Image Correlation, was used in order to detect the 3D displacement and strain fields, and to evaluate the twist angle of the entire external surface, with particular attention to the interface area. The preliminary results prove the reliability of the test bench and confirms the piezo-resistive response of the anaerobic adhesive.

Fatigue properties of self‐piercing riveted multi‐rivet joints in steel and aluminum sheets

AbstractSelf‐piercing riveting (SPR) is an important joining technology for connecting steel and aluminum sheets. In this paper, AA6111 aluminum alloy and DP780 high‐strength steel were adopted to study the influence of fatigue on remaining static strength and energy absorption properties on self‐piercing riveting multi‐rivet joints. The results showed that energy absorption capacity of the specimens decreased significantly after high cycle fatigue. Fatigue reduced the remaining static lap shear strength of riveted specimens. Scanning electron microscopy (SEM) was used to analyze the cross section of fatigue specimens fractured by static tension. The results showed that fretting wear was found at the contact area between rivet and aluminum sheets. Fatigue bands and fatigue cracks appeared in fatigue specimens after high cycle fatigue, while those with low cycle fatigue specimens did not appear. Small cracks weaken the strength of the aluminum sheet, resulting in the static tensile strength of the riveted specimen with high cycle fatigue is lower than that of other fatigue specimens.

A new model for evaluating the dynamic shear strength of rocks based on laboratory test data for earthquake-resistant design

The dynamic shear strength of rocks is required for the earthquake-resistant design of nuclear power plants in Japan. This research aims to propose a mathematical model for estimating the dynamic strength and to validate the model. Two different types of specimens were prepared for the model validation, and the monotonic and cyclic loading tests were conducted to obtain the mathematical model parameters. Subsequently, multistep cyclic loading tests were performed, followed by simulations using the mathematical model. The test results demonstrated that the dynamic shear strength exceeded the static shear strength, which agreed with previous researches. Furthermore, the dynamic shear strength calculated using the mathematical model was generally consistent with that obtained from the experimental data.

Effect of Repetitive Collar Replacement on the Residual Strength and Fatigue Life of Retained Hi-Lok Fastener Pins

Hi-Lok fasteners were subjected to multiple collar replacements, and were tested under static loading and constant-amplitude fatigue loading, to determine the effect of repetitive collar replacement on the residual strength and fatigue life of a retained Hi-Lok-type fastener pin. Hi-Lok-type fasteners are typically used in aircraft structural joints, and are loaded mainly in shear. Tests were conducted for clamping force, static shear strength, static tensile strength, and shear fatigue life for collars subjected to five collar replacements. The static shear results showed no decrease in the ultimate shear strength of the fastener pin as a function of collar replacement. Static tensile results showed no decrease in the ultimate tensile strength of the fastener as a function of collar replacement, with failure of the aluminum collar remaining the critical failure mode. Similarly, shear fatigue results showed no decrease in the shear fatigue life of the fastened joint as a result of collar replacement, with fracture of the aluminum substrate remaining the critical failure mode. For static shear, static tension, and shear fatigue tests, estimated clamping force was highly consistent between specimens and no decrease in clamping force was observed as a function of collar replacement.

Experimental simple shear study of composite soil with cemented soil core

Cement soil mixing piles are an effective treatment method for marine soft clay. To investigate the static and dynamic characteristics of the composite soil with cemented soil core, a series of experiments are carried out by using the cyclic simple shear test. The result shows that, the static shear strain showed strain hardening, cemented soil core can improve static shear strength of composite soil, vertical stress can enlarge reinforcement of cemented soil core. The tendency of strain development of composite soil with different area replacement ratios under cyclic loading is the same as that of pure clay, existing critical cyclic stress ratios corresponding to different area replacement ratios. In addition, improving area replacement ratio can increase cyclic strength. At same time, adding of cemented soil core does not change shape of hysteresis curve compared with it for clay either. Moreover, cemented soil core can also obstruct stiffness softening. Through regression analysis of the experimental data, relationship between cyclic number and soil softening index is proved to be linear. The results can give a reference for the dynamic characters of the marine soft clay foundation with cement soil mixing piles.

Fracture Toughness and Strength of the Interface of an Intrinsic Hybrid Laminate

Unidirectional glass fiber reinforced plastic (U-GFRP) represents itself as an excellent lightweight structural material due to its high tensile strength Rm and its low density ρ. A major drawback, however, is the relative weakness of the matrix under more complex, multi-axial loading conditions. Therefore, a local hybridization of U-GFRP seems to be an adequate measure to enhance the robustness of the material. First, the material testing program sets the focus on the investigation of the strength of the interface between U-GFRP and the additional constituent steel. Hence, the energy release rate GI, the static shear strength ts as well as the cyclic shear strength τs,cyclic of the considered interface have been determined at room temperature RT and at an elevated temperature of T = 80° Additionally, aged specimens have been statically tested as well. The results show up that primers, such as silane, are leading to a good adhesion between the constituents. Furthermore, a fiber bridging effect is apparent which leads to an increase of the energy release rate GI with the growth of the length a of the crack. A power law is well suited to describe this strengthening and its exponent n serves as a further measure to describe the strength of the interface. Generally, ageing of the material and straining at an elevated temperature harm the performance of the intrinsic hybrid material.

Post-cyclic shear behavior of reconstituted marine silty clay with different degrees of reconsolidation

In this paper, a series of dynamic triaxial tests have been carried out to study the post-cyclic shear behavior of the reconstituted marine silty clay. Most previous studies on the post-cyclic shear characteristics of clay considered no reconsolidation after cyclic loading, and a few studies investigated the influence of full reconsolidation. The actual marine clay after cyclic loading tends to be in a state between no reconsolidation and full reconsolidation after cycling. Therefore, different reconsolidation processes including no reconsolidation, full reconsolidation and different degrees of reconsolidation were conducted to investigate their effects on the post-cyclic shear characteristics. Various factors including confining pressure, initial consolidated deviator stress ratio, cyclic stress ratio and degree of reconsolidation were taken into account. Results show that the post-cyclic shear strength will be enhanced and weakened with the full and no reconsolidation, respectively. And a specific degree of reconsolidation is existed for the specimens, with which the post-cyclic shear strength equals to the corresponding static shear strength. During the post-cyclic monotonic shear process, the silty clay always have a positive pore pressure and show dilative tendency. Moreover, no significant effects of cyclic loading and reconsolidation history on the change of critical stress ratio in p′-q plane was observed for the reconstituted silty clay. The critical stress line for specimens in e-log p′ plane tends to be affected by the previous cyclic loading amplitude, irrespective of the reconsolidation process. Besides, a post-cyclic shear strength model which can consider different degrees of reconsolidation was obtained based on the Yasuhara equivalent overconsolidation model. The predicted results demonstrate a good agreement with the measured one.

Cyclic robustness of heavy wire bonds: Al, AlMg, Cu and CucorAl

Development of advanced electronic packages can be drastically affected by implementation of new materials. The ever increasing demands for high performance and reliable power electronics, raise the need for rapid robustness evaluation of interconnects. In this study the lifetime of heavy wire bonded interconnects, fabricated with different wire material types Al, AlMg, Cu and Al coated Cu (CucorAl) bonded onto direct copper bonded ceramic substrates was investigated. The tests were performed using an accelerated mechanical fatigue testing system, which allows to determine the lifetime of the interconnects with regard to wire bond lift-off failure in a short period of time. Thus, the influence of ultrasonic power variation and the impact of aging on the performance of wire bonds with different material combinations was studied. Cu wire bonds showed clearly the best fatigue performance as well as static shear strength followed by AlMg and Al bonds. Increasing the ultrasonic power results in a higher fatigue resistance of CucorAl in comparison to pure Al wires. In certain cases, the results of the fatigue experiments and static shear tests were found to be contradictory. The presented results suggest that accelerated mechanical fatigue testing can be used as an additional fast method for qualification of interconnects and assessment of the influence of wire material, bond parameter and aging.

Mechanical performance of laser spot-welded joints in Al-Al/Cu solar thermal absorbers

The mechanical performance of laser spot welded joints used in Al-Cu and Al-Al thermal absorber systems has been evaluated under different laser welding and mechanical loading conditions. In the experimental investigation, the effect of laser pulse shape and laser heat input on the spot weld strength has been examined under static and cyclic shear loading. The residual strength of spot welds after initial cyclic loading has also been evaluated. The experimental results are supported by metallographic analysis of welds and fractography of failed spot welds. It is concluded that the static and cyclic shear strength is primarily influenced by the laser heat input, which regulates the size of the generated laser spot weld section and to a lesser extent by the laser pulse shape. The influence of laser heat input parameter on the mechanical performance seems not to be as severe in the case of residual strength. This may be associated with the presence of brittle intermetallic compounds in the bimetallic Al-Cu welds which induce small scale defects during the welding process, thus further affecting mechanical performance leading to a reduction of the load bearing capacity of the spot weld.

Seismic Stability of a Tunnel Considering the Dynamic Geologic Parameters of Loess

In this study, Taiyuan loess is used in the analysis of the seismic stability of a loess tunnel. This analysis considers the dynamic parameters of the loess as determined via triaxial compression tests in the literature. In this analysis, the consolidation pressure is converted into the thickness of the overlying loess layer. The spring stiffness and damping coefficients of the viscoelastic boundary are obtained using the maximum dynamic elastic modulus in conjunction with different loess moisture contents and Poisson’s ratios. Additionally, the loess cohesion and internal friction angle are also obtained for different moisture contents. By (1) utilizing the dynamic finite element static shear strength reduction method and the non-convergence rule, (2) taking the safety factor as the assessment standard for loess tunnel stability, and (3) reducing the dynamic parameters of the loess mass until the model calculation is non-convergent, the effects of the moisture content, seismic intensity and loess thickness on the safety factor are obtained. A theoretical basis for the seismic response analysis of this type of loess tunnel is provided by considering the dynamic parameters of loess.

Influence of Corrosion of Self-Piercing Riveted High Strength Aluminium Alloy Joints with Button Cracks on the Mechanical Strength

For high strength aluminium alloys, such as AA6008T61 and AA6111 PFHT, when they are joined as the bottom material by self-piercing riveting (SPR), they tend to crack at the joint buttons. These cracks, especially those penetrated to the rivets, may cause galvanic corrosion problem with the steel rivet. In this paper, the mechanical strength of four stack/die combinations with different joint button cracking severity was studied before and after salt-spray corrosion test. The results showed that corrosion on the severely cracked joints was worse than that on the joints with small cracks and the corrosion on the stack with the same top and bottom material was less than that on the stack with different top and bottom materials. For all joints the static lap shear strength after corrosion was improved, but the static T peel strength after corrosion was slightly reduced or did not have obvious change. The results also showed that after corrosion the lap shear fatigue strength of the specimens with severe cracks did not have obvious change, but the lap shear fatigue strength of the specimens with small cracks slightly reduced.

Effect of sample disturbance on cyclic shear strength of normally to lightly OC clays

Tests on Onsøy clay (Ip = 24–27%) were performed to study the effect of sample disturbance on undrained static and cyclic shear strength. Samples with different degree of disturbance from sampling were used and parallel sets of monotonic and cyclic undrained laboratory tests were performed on block and 54 mm composite piston samples. A silty Drammen clay (Ip = 19%) which was studied earlier was included in the study. Test results indicated that there are significant effects of sample disturbance on both static and cyclic undrained shear strengths for both Onsøy and silty Drammen clays.

Fatigue of adhesively bonded epoxy-AA6061T651 joints

Purpose Adhesively bonded joints are gaining importance in the structural joining processes competing against welding and bolting processes. However, long-term behaviour of adhesively bonded joints is still an open question. Due to the increasing interest in adhesively bonded joints, mainly in the transports industry, there is a need to deep the knowledge about the fatigue behaviour of adhesive joints with metallic substrates allowing the development of reliable joints to resist cyclic loadings. The paper aims to discuss these issues. Design/methodology/approach An experimental research aiming at characterizing the fatigue behaviour of adhesively bonded aluminium substrates is presented in this paper, covering both fatigue crack propagation and global S-N behaviours. Double cantilever beam (DCB), end notch flexure (ENF) and double lap joints (DLJ) specimens built using the AA6061T651 substrate and epoxy adhesive were used to evaluate the pure modes I and II fatigue crack propagation rates and the S-N fatigue behaviours. Findings DCB and ENF specimens allowed the formulation of pure modes I and II fatigue crack propagation laws including the propagation thresholds. DLJs showed higher static shear strength than recommended by the manufacturer for aluminium substrates, but fatigue resistance of the DLJs was lower than suggested by the manufacturer. The fatigue damage process in the DLJs was dominated by a fatigue crack initiation process. Originality/value A consistent fatigue research on adhesively bonded aluminium substrates is presented covering in the same study aspects of fatigue crack propagation and fatigue crack initiation. Data reduction schemes involving both numerical and analytical procedures were followed. Proposed work constitutes a rigorous basis for future fatigue prediction models developments.

Breakout shear strength of cast-in-place anchors using shaking table tests

The concrete breakout shear strength of stirrup-reinforced cast-in-place anchors during earthquakes was experimentally evaluated. Uncracked and cracked concrete specimens were manufactured using M36 anchors reinforced with D10 stirrups (spacing, 100 mm; edge distance, 180 mm). Shaking table tests were performed to assess the dynamic strength of the reinforced anchors using the Northridge seismic wave. The experimental results showed that the dynamic shear resistance was slightly higher than the static shear resistance due to the strain rate effect of the material. In addition, Etag 001, which is based on the resistance of concrete, and ACI 318, which accounts for the resistance of concrete or steel reinforcement to evaluate the strength of the reinforced anchors, yielded conservative values for the static and dynamic shear strengths of the stirrup-reinforced anchors. An appropriate method that can account for both concrete and stirrup resistance to evaluate the design shear strength of stirrup-reinforced anchors under earthquakes is proposed.