Static Strength Research Articles

Influence of Machining Modes and Negative Temperature on the Static Bending Strength of Carbon Fiber Reinforced Plastics

Influence of Machining Modes and Negative Temperature on the Static Bending Strength of Carbon Fiber Reinforced Plastics

Mechanical Properties of Titanium Grade 1 After Laser Shock Wave Treatment

Abstract In the presented work the impact of a laser shock wave on the mechanical properties of a Titanium Grade 1 was investigated. Based on a series of experimental studies related to the impact of the laser shock wave on the tested material, the impact of the given treatment on the structure and mechanical properties was assessed. The influence of the environment on the distribution of plasma temperature and pressure in the material during the implementation of the laser shock wave was analyzed. The effect of the laser treatment on the structure and micromechanical properties was initially estimated on the basis of the analysis of experimental results in the form of static strength test of samples after laser treatment. A slight increase in material strength was detected with a minimal decrease in ductility. In order to comprehensively understand the observed phenomenon, a number of fractographic tests were performed, especially the analysis of the porosity of the fracture surfaces. A decrease in the porosity of the material after impact laser treatment was observed as a result of local plastic deformation.

Static strength and crashworthiness analysis of a train cowcatcher at a running speed of 160 km/h

The cowcatcher is one of the unique devices at the front end of the train, which can remove obstacles on the track by crashing before the vehicle body to ensure the safety of the train. When a collision accident happens, the cowcatcher serves as the first energy-absorbing structure to dissipate and guide the collision energy. The design of the existing cowcatcher of multiple units generally focuses on the good ability to remove obstacles, while the secondary function, the crashworthiness of orderly deformation under collision, still needs further research. In this study, a finite element model of structural static load and collision analysis was established under standard EN 15227, with the cowcatcher for 160 km/h train as the prototype. Then the solution and simulation process was accomplished under the environment of ANSYS and LS-DYNA. The analysis results showed that the structural static strength of the current cowcatcher met the requirements of the standard EN 15227, and the longitudinal stiffness was evenly distributed. When removing the obstacles with low mass, the impact force was small and the structure would not produce obvious deformation; when removing the obstacles with large mass, the impact force was large and the shear fracture might occur at the connection of the cowcatcher.

Effect of double-step pore defects on connection properties of carbon fibre reinforced plastics/Ti laminated components

The composite structure composed of carbon fiber reinforced composite and titanium alloy is widely used in aviation and aerospace fields. Due to the different physical properties of these two materials, in the process of lamination, it is easy to appear the pore in the direction of thickness is inconsistent, which is called double-step pore defects (DSPD). The existence of DSPD will undoubtedly have an impact on the connection performance of components, but there is no clear conclusion on the extent of its impact on the connection performance, which restricts the improvement of the pore quality evaluation system, and may cause a waste of resources or leave a safety hazard for aircraft. To solve this problem, the finite element model was established to analyze the initial damage phenomenon of the component with DSPD during bolt tightening. The influence of DSPD on the static strength and fatigue properties of the component was studied by designing experiments, and the failure mechanism was revealed from the perspectives of failure form and damage evolution. The purpose of this study is to provide guidance for the improvement of the evaluation standard and the high quality and stability of the lamination component.

Study on mechanical property and breakage behavior of tunnel slag containing weak rocks as road construction material

In the construction of roadbeds in mountainous areas, crushed rock slag (CRS) generated by tunnel blasting is usually reused as road construction material to reduce environmental pollution and construction costs. A series of large-scale drained triaxial tests were conducted to investigate the mechanical behavior of CRS subjected to static and traffic loading. The static triaxial tests determined the maximum stress level that can be applied to the cyclic test. The cyclic triaxial test analyses the influence of cyclic stress amplitude and confining pressure on the cumulative strain of CRS material. The particle breakage of the sample under various conditions after cyclic loading was discussed, and the relationship between the relative breakage index and the final accumulated strain was analyzed. Test results indicated that with the increase in confining pressure, the peak strength of the material exhibits a continual enhancement, while the expansion behavior experiences a gradual attenuation. In the range of static failure strength, the increase of cyclic stress level will significantly increase the accumulated axial strain rate. After the cyclic loading, the particle breakage patterns are similar under different confining pressures. A good power function relationship exists between the relative breakage index and final axial strain, and further derivation of the functional expression of the relative breakage index and both cyclic stress ratio and confining pressure.

Geometry effect on the static strength of curved composite bonded joints

In this work, the behavior of composite curved adhesive joints under pressure (p) is analyzed; such joint configuration has applications in aircraft fuselages. The chosen substrates were Carbon-Fiber Reinforced Polymer (CFRP) and three substrate thicknesses (tP) were studied. In addition, three different curvature radii (R), and eight overlap lengths (LO) were evaluated, while only one adhesive type was used. An internal pressure of 1 MPa was considered in all cases. The analyses were performed using the finite element method (FEM) and cohesive zone modelling (CZM). The increase in LO causes a linear increase in the peak peel stresses (σyy), affecting the thinner joints more; these peak stresses were located in the joint's knee region. Pmax was also found influenced by tP and LO, being again the effect more noticeable on the thinnest substrate; however, for LO≥40 mm the effect was negligible. As tP increased, Pmax had no significant improvement for LO≥20 mm. Although increasing R causes a slight reduction in the peak stresses, the stresses along the bond line were more uniform. Although R had no significant effect on Pmax, it increases joint compliance. In conclusion, the chosen adhesive allowed to successfully explore the different geometric parameters where the thinner joints with the largest R showed the best performance.

Suffusion in densely compacted Satozuka pumice sand and its impact on static loading undrained shear strength and dilation behaviour

Pumice sand of volcanic origin contains a high fraction of non-plastic fines (>40 % for Satozuka pumice sand in Sapporo, Japan). Suffusion in such soil can wash away a portion of the fine particles and alter the soil microstructure. The moisture content and degree of compaction can affect the suffusion characteristics of soil deposits, however their effect has not yet been evaluated. Future construction sites in growing Sapporo City, consisting of pumice sand, will require a high degree of compaction (over 90 % and preferably over 95 %) as this sand is prone to suffusion in spite of its dense state. The aim of this study is to assess the impact of suffusion on densely compacted pumice sand with a high proportion of fines, based on its mechanical properties, with an emphasis on shear strength and dilatancy. Firstly, the suffusion characteristics of Satozuka pumice sand were evaluated. Subsequently, undrained triaxial tests (CU¯ tests) under monotonic loading were conducted on high-density specimens, with suffusion and without suffusion, to study the impact of suffusion. It is seen in the results that the hydraulic conductivity, shear strength, stress paths, and dilatancy are all noticeably affected by suffusion. The specimens with suffusion exhibit an increase in residual shear strength and maximum deviator stress under shearing and experience an earlier occurrence of phase transformation from contraction to dilation during shearing. This tendency implies that suffusion has no significant negative impact on the deterioration of earth fill made from pumice sand and non-plastic fines, and that it persists at degrees of compaction between 80 % and 100 %.

Effects of fiber characteristics and specimen sizes on static and dynamic split-tensile failures of BFLAC: 3D mesoscopic simulations

In this study, a three-dimensional mesoscopic numerical model considering concrete heterogeneity and explicit modelling of basalt fibers was established to simulate the static and dynamic split-tensile failures of basalt fiber-reinforced lightweight aggregate concrete (BFLAC), with a special focus on the influences of structure sizes (D = 100, 200, 300 and 400 mm), basalt fiber contents (Vf = 0.1 %, 0.2 % and 0.3 %), fiber lengths (Lf = 6, 12, 18, 24 mm) and loading strain rates (ε̇ = 10-5/s ∼ 100/s) on split-tensile failure patterns, deformation characteristic and failure strengths. Simulation results indicate that as the fiber length increases, split-tensile strength of BFLAC enhances first and then remains unchanged. As the fiber content increases, both static and dynamic split-tensile strengths enhance, showing a fiber reinforcement effect which increases with the rising strain rate rise and reaches a threshold when the strain rate exceeds 1/s. Under static and low strain rates, the size effect on split-tensile strength of BFLAC is reduced by the addition of basalt fiber content; while there is a reverse size effect under high strain rates and it is strengthened with the increasing fiber content. Besides, the strain rate effect of BFLAC is stronger with the increasing basalt fiber content. A unified TDIF formula of BFLAC considering the influence of basalt fiber content was proposed, which can provide a valuable reference for the dynamic performance simulations and calculations.

Mechanical properties and constitutive models of butt-welds in Q345GJ thick steel plates

GJ steel is a high-performance steel manufactured in China, and its thick plates are widely used in building structures. The first companion study examined the material properties of the thick GJ steel plates (t ≥ 60 mm). This study focuses on the mechanical properties of butt welds in thick GJ steel plates (t ≥ 60 mm). Monotonic and cyclic tests were conducted on butt-weld specimens made of 60-mm and 100-mm thick Q345GJ steel plates in the longitudinal and transverse directions. In addition, the layered specimens obtained from five different thickness locations were tested. Based on the cyclic test results, the Chaboche constitutive parameters were calibrated and verified via the finite element analysis (FEA). Moreover, the differences in the static and cyclic mechanical properties of the base metal and butt welds were analysed. Compared with the base metal, the static tensile strength and hysteretic energy dissipation under the same cyclic loading protocol were better in the weld specimens; however, their ductility was significantly lower. Furthermore, the distribution of the mechanical properties along the thickness direction was more uniform in the weld specimens. Moreover, the weld specimens had higher yield surface reduction ratios. However, their initial and final yield surface sizes were larger than those of the base metals.

Study on dynamic splitting tensile mechanical properties and microscopic mechanism analysis of steel fiber reinforced concrete

With high compressive strength and high fracture toughness, steel fiber reinforced concrete is widely used in large-span bridges and high-rise buildings. Since concrete structures are subjected to strong dynamic loads such as impact blast during service, it is essential to clarify the dynamic mechanical behavior of steel fiber reinforced concrete and to propose an adapted dynamic constitutive model for structural dynamic response calculation. Therefore, in this paper, a static and dynamic splitting tensile test study was conducted on steel fiber reinforced concrete with four fiber contents (0%, 1%, 2%, and 3%), and a separated Hopkinson compression bar (SHPB) was used to conduct dynamic splitting tensile tests on steel fiber reinforced concrete to obtain the failure pattern, stress–strain curves, and basic mechanical parameters of steel fiber reinforced concrete. The results showed that the static and dynamic splitting tensile strength of steel fiber reinforced concrete increased with increased steel fiber content. The dynamic splitting tensile strength and peak deformation of steel fiber reinforced concrete increased significantly with increasing strain rate, and the dynamic splitting tensile strength of steel fiber reinforced concrete increased in the range of 1.1 to 3.3 compared with static splitting tensile strength. The enhancement of dynamic splitting tensile strength with increasing strain rate at different fiber contents showed a significant and then flattening trend. In addition, the dynamic splitting tensile strength and strain-rate sensitivity of non-steel fibered concrete are higher than that of steel fiber reinforced concrete. Meanwhile, the X-CT scanning technique was applied to reveal the strain rate reinforcement and steel fiber reinforcement mechanism from the microscopic perspective. Finally, the K&C model was modified based on the experimental results and applied to the dynamic splitting tensile simulation of SHPB to verify the accuracy and adaptability of the proposed constitutive model. The research results finally provide a theoretical basis for the mechanical response of steel fiber reinforced concrete structures under impact blast.

Enhancing the dynamic splitting tensile performance of ultra-high performance concrete using waste tyre steel fibres

The application of waste fibres in ultra-high performance concrete (UHPC) would reduce the total material cost of UHPC, but it is still unclear whether industrial fibres can be replaced by waste tyre fibres in terms of the impact resistance. In the present work, a series of experiments were performed to figure out the influence of waste tyre steel fibre (WF) content (i.e., 1.0 %, 2.0 %, 3.0 % and 4.0 %) on the workability, compressive strength, elastic modulus, flexural strength and dynamic splitting performance of UHPC, in comparison with plain UHPC containing 2.0 % industrial straight steel fibre (IF). The results reveal that the slump of UHPC is reduced with the increasing WF fibre content, but the flexural and static splitting strengths of UHPC are improved by up to 31.0 % and 24.7 %, respectively, within the measured WF content. Moreover, the dynamic splitting strength and dissipation energy of UHPC are promoted when the WF content is lower than 3.0 %, while an opposite trend takes place as the content of WF reaches 4.0 %. Additionally, the dynamic increase factor of WF reinforced UHPC shows higher sensitivity to strain rate than UHPC containing 2.0 % IF throughout the strain rate range of 2.0 s−1–6.5 s−1. The optimal WF content of UHPC can be regarded as 3.0 % considering the overall static strengths, dynamic splitting behaviour, as well as economic and ecological impact.

Study on the peeling criterion of anti-ice and wear-resistant coating for polar ships and simulation analysis method of the ship-ice collision process

The wear-resistant coating on the hull surface can be peeled off under the collision between the ice during the navigation of polar ships. In this study, the damage and peeling of the anti-icing wear-resistant coating at different impact angles, impact speeds, and temperatures were simulated. The static icing adhesion shear strength and normal peel strength of the anti-ice wear-resistant coating were examined, and the coating peeling criterion with temperature term was proposed. Furthermore, the damage and peeling of the anti-ice wear-resistant coating at different impact angles, impact speeds, and temperatures were simulated numerically.

Static Strength of Tubular K-Joints Reinforced with Outer Plates under Axial Loads at Ambient and Fire Conditions

In this paper, the effect of the outer reinforcing plate on the initial stiffness, ultimate strength, and failure mechanisms of tubular K-joints under axial load at ambient and different fire conditions is evaluated. In the first phase, a finite element (FE) model was generated and verified by 13 experimental tests. In the next step, 1057 numerical models were generated. In these models, the welds joining the chord and braces were modeled. Using the produced FE models, the structural behavior under ambient and different elevated temperatures (20, 150, 300, 450, 600, 750, and 900 °C) was evaluated. The results showed that the outer plate can enhance the ultimate strength by up to 319% under fire conditions. Despite the considerable effect of the outer plate on the stiffness, ultimate strength, failure modes, and the frequent usage of the K-joints in tubular structures, the static response of the reinforced K-joints at ambient and elevated temperatures has not been studied. Hence, according to the extensive parametric studies, a highly precise practical design equation has been proposed based on the yield volume model for determining the ultimate strength.

Characterization of a short fiber-reinforced adhesive designed for wind turbine rotor blades

Wind turbine rotor blades are usually made of two half-shells and shear webs that are joined together by structural adhesives. The adhesive joints suffer from longitudinal strains from blade bending combined with shear strains from torsion and shear forces acting on the blade. It is thus important to provide an accurate and reliable characterization of the adhesive as a bulk material to account for cohesive failure.This work focusses on the characterization of a short fiber-reinforced adhesive used in wind turbine rotor blades under uniaxial tension, compression, and shear as well as biaxial tension-compression/shear for both static and fatigue loading. To obtain small scatter in measurement results, a specimen geometry was designed that ensures a clear maximum stress in the test section while minimizing stress concentrations in the transition between the load introduction regions and the test section. The manufacturing process was then designed in such a way that an optimum mixture of resin and hardener was obtained without the inclusion of voids. The latter was verified after manufacturing by means of micro-CT scanning for all specimens. A very extensive test campaign was then carried out in order to quantify stiffness, static strength, fatigue strength, and fatigue-related stiffness degradation. Excerpts of this test campaign are presented in this paper.

Analyzing the impact of veneer layup direction and heat treatment on plywood strain distribution during bending load by digital image correlation (DIC) technique

In this study, radiata pine veneers and phenol-formaldehyde resin were used to prepare specimens of 5-ply plywood with different layup directions and heat treatments of veneers. The physical and flexural properties of the plywood specimens were assessed, and digital image correlation (DIC) analysis was employed to determine the strain distribution of the plywood under bending loads. The results of the static mechanical strength and DIC tests showed that the plywood with a small-angle veneer layup ([0]5 and [0,22.5,0,22.5,0]) exhibited a better longitudinal modulus of rupture (MOR//), while [0,45,0,45,0] plywood showed the least bending strength and most strain. Moreover, the results revealed that for plywood composed of veneers that were fully heat treated at 200 °C (5T200), the moisture content was efficiently decreased, and the modulus of elasticity parallel to grain (MOE//) was the highest. The DIC images indicated that the largest strain along the x-direction (εxx) was concentrated on the tensile side of untreated plywood (5N) and on the opposite side of plywood composed of heat-treated veneers, except for the plywood composed of veneers treated at 220 °C (5T220). Of these, 5T200 plywood showed the least strain. In addition, the plywood with 200 °C heat-treated veneers instead of face and core layers (NTNTN200) or crossband layers of untreated veneers (TNTNT200) had larger strain values than 5N and 5T200 plywood specimens, with NTNTN200 plywood having the greatest strain. According to the above results, appropriate layering and heat treatment of veneers can effectively improve the dimensional stability and flexural properties of plywood.

Quantification of process-induced effects on fatigue life of short-glass-fiber-filled adhesive used in wind turbine rotor blades

Cracks in the adhesive joints of wind turbine blades can often cause severe structural blade damage. Effects induced by the manufacturing process can have a significant impact on the cycle number toward crack initiation in the bonding material. This research compared two experimental series of neat adhesive, dog-bone-shaped specimens with different degrees of cure, fiber orientation, and porosity content, which were subjected to static and cyclic tension-tension loading. To enhance the comparability of the two coupon series, the experimental data was normalized. Normalization factors were introduced to compensate for the different properties of the two series. These factors were derived from correction models. After normalization, the S-N values of the two data series were in good agreement in the high-cycle fatigue regime. In the very-low-cycle fatigue regime, however, there was still a lack of agreement in some cases, including the static strength. Moreover, the failure mechanisms were investigated by analyzing images from the fracture surfaces and dedicated samples using X-ray microscopy. The correction models presented can be applied to estimate the design strength of adhesives. This knowledge can then be used to make rotor blade structures more resistant to crack initiation.

Static compression behavior and strength weakening mechanism of dynamically damaged granite after water soaking

In backfill mining, the surrounding rock is dynamically damaged by intermittent mining and blasting. After backfilling, bleed water from the backfill seeps into the surrounding rock, leaving the surrounding rock in a water-rock coupling environment. To study the mechanical properties of surrounding rock in such a scenario, two types of granite specimens were prepared, namely, impact-damaged (ID), impact-damaged and water-soaked (IDWS) specimens. A modified split Hopkinson pressure bar (SHPB) system was first applied to execute the dynamic tests with different impact numbers and confining stresses to prepare the ID specimens. Subsequently, the IDWS specimens were prepared by water soaking tests on half numbers of the ID specimens. Finally, static uniaxial compression tests were performed on ID and IDWS specimens. The test results indicate that the peak strength of ID and IDWS specimens increases with the increase of confining stress, and first increases and then decreases with the increase of number of impacts. The total strength weakening factor of the IDWS specimens is composed of the impact strength weakening factor and the water-induced strength weakening factor, as well as the coupling effect of the two factors. Impact loading increases the number of microcracks and pores inside the IDWS specimens, resulting in a larger contact area between water and microcracks and pores. Compared with ID specimens, water induces more tensile cracks in the IDWS specimens according to the results of electron microscope scanning. This is manifested as the transfer from macro shear failure mode to macro tensile failure, and further reduces the peak strength of the IDWS specimens.

Devising procedures for design and verification calculations of the beam-wall with edge breaks under static and cyclic loads

This paper considers a thin-walled steel beam-wall with broken edges, which is part of many structures. The wall of this beam consists of two prismatic parts with a straight transition from a lower wall height to a higher one, forming a broken upper edge together with the edges of the prismatic parts. The bottom straight edge of the wall is attached to the cladding. The beam-wall is affected by static and cyclic nominal loads, which can cause the appearance of elastic-plastic deformations in the stress concentrator. This causes non-fulfillment of static strength and the appearance and growth of fatigue cracks. In the current work, procedures of design and verification calculation of a steel beam-wall with fractured edges at elastic static and cyclic elastic-plastic deformation in the stress concentrator are proposed. The material of the beam is ideal elastic-plastic. Features of the procedures are the possibility of optimal design under conditions of elastic and elastic-plastic deformation, using dependences only for optimal elastic design. A distinctive signature of the procedures is that, through Neiber's formula, elastic-plastic characteristics are not determined by known elastic ones, as usual, but vice versa. According to the established dependences for cyclic elastic-plastic deformations in the concentrator, the theoretical concentration coefficient is determined, which, in turn, is involved in determining the optimal geometric parameters. The procedures give reliable results with nominal symmetrical cyclic loads up to 0.6 of the yield strength. This is because Naber's formula always yields conservative results, causing excess strength. The procedures can be applied separately for stretching-compression and bending, and with their combined action

Static strength design of local thickened plate joints between multi-cell concrete-filled steel tubular column and steel beam

A new-type local thickened plate joint (LTPJ) between multi-cell concrete-filled steel tubular columns (CSTC) and steel beams is adopted in residential building structures. However, no available strength design method for such beam-column joints is reported. This paper presents the mechanical behavior and static strength design of such joints. The local thickened plates are adopted to replace the normal thickness plates of the CSTCs within the LTPJ region. The rectangular section and L-shaped section of the multi-cell CSTC are involved in the joint study, respectively. Firstly, a finite element model (FEM) of the LTPJ between CSTCs and steel beams is established, which is then adopted to investigate the mechanical behaviour and static load-bearing capacity of the LTPJ. Codirectional and inverse bending moments are applied on the beams on two opposite sides of the LTPJ to simulate lateral loads (arise from wind or earthquake) and dead gravity loads, respectively. It is revealed that the LTPJ experiences shear failure when subjected to lateral loads, whereas it succumbs to bending failure when under dead gravity loads. The shear-bearing capacity of the LTPJ results from the three-part contribution of the steel tube web, the steel tube flange, and the core concrete. The bending-bearing capacity of the LTPJ is determined by the plate normal tension-bearing capacity of the steel tubes, which is predicted by adopting the theory of yielding line and numerical fitting. Finally, the load-bearing capacities of LTPJ under bidirectional bending moment are investigated numerically, and accordingly, some strength design recommendations are proposed in practical application. To conclude, these results provide a method for accurately predicting the load-bearing capacity of the LTPJ subjected to lateral loads and gravity loads, which holds the potential to expand and enhance the application of LTPJs and CSTCs in the design of high-rise residential buildings.

The effect of recycled date palm tree fibers on the impact fatigue and residual static strength of adhesively bonded joints

The role of natural fibers on the impact fatigue strength of bonded single lap joints (SLJs) has been experimentally investigated. The use of natural fiber offers several advantages, including the potential to recycle natural resources and the utilization of sustainable materials. Four types of natural date palm tree fibers (DPTFs) including Rachis, Petiole, Bunch, and Mesh were used to improve the impact fatigue life and the residual static strength of joints after enduring repetitive low energy impacts. The fibers were treated by 6 wt% of NaOH solution and cut manually to short size (0.5–2 mm) and were used by weight ratios of 2 and 5 %. The results show that the addition of DPTFs to the adhesive layer significantly improves the impact fatigue strength of the reinforced joints compared to neat adhesive SLJs. The joints reinforced by 5 wt% and 2 wt% of Mesh improved the impact fatigue life of the joints by 197 % and 87 %, respectively. The impact fatigue life of the joints modified by 5 wt% of fibers was more than the joints reinforced by 2 wt%. Fractography analysis also showed that DPTFs make the crack propagation more stable and increase the strength of the tested joints on different conditions.