Tensile Impact Loading Research Articles

An improvement of shape memory effect in Fe-Mn-Si shape memory alloy by training process under impact tensile loading

The effect of impact-load training on shape recovery has been investigated in an Fe-based shape-memory alloy. The Fe-28Mn-6Si-5Cr alloy samples underwent repeated training involving 7 % tensile straining followed by subsequent heat treatment. The results indicated that shape recovery after heating improved with an increasing number of training cycles under both quasi-static and impact loading conditions. However, beyond seven training cycles, only marginal improvements were observed for both loading conditions. The ratio of shape recovery under impact loading condition was higher than that under quasi-static condition after the fifth training cycle. The recovery strain achieved after six cycles of impact-loading training was 93 %. Volume resistivity measurements revealed that the threshold stress required for forward martensitic transformation decreased with an increasing number of training cycles. In addition, the effect of impact-loading training was examined using electron backscatter diffraction (EBSD) measurements. From the EBSD analyses after loading, the martensite generated under the impact loading condition was predominantly a single variant in a grain, whereas multiple variants were frequently detected after quasi-static loading.

Dynamic spall properties of an additively manufactured, high-entropy alloy (CoCrFeMnNi)

The dynamic spall properties of an additively manufactured (AM), CoCrFeMnNi high-entropy alloy (HEA) were investigated as a function of processing defects. Laser Powder Bed Fusion (LPBF) was used to additively manufacture HEA samples that were subsequently subjected to shock loading through plate impact experiments. Seven different combinations of laser power and scan speeds were explored, ranging from 180 to 280 W and 925–1350 mm/s, respectively. All samples were considered within the bounds of lack-of-fusion and keyholing defects based on initial experiments, but exhibited varying degrees of solidification cracking and microstructural changes. Grain size and grain aspect ratio were found to modestly decrease with faster scan speeds and lower laser powers, while cracking associated with the AM process increased with faster scan speeds and higher laser powers. Spall strength and spall damage did not systematically trend with microstructural characteristics such as grain size, but did exhibit a relationship with pre-existing crack density. Spall properties were found to generally degrade with increasing crack density. Evidence of defect compaction was not observed in soft recovered spall samples, thus pre-existing cracks were proposed to degrade spall properties by acting as stress concentrators and preferred damage nucleation sites during tensile impact loading. Here, the presence of manufacturing-related defects, such as cracks, dominated the dynamic response; however, in the absence of these defects, microstructural changes like grain size and texture would be expected to control dynamic behavior.

Brittle fracture development through sets of preexisting small-scale cracks under quasi-static and dynamic impact loading

Fracture development and its possible relation with wave motion in a brittle rectangular solid material with sets of preexisting small-scale parallel cracks are investigated. Experimental observations using high-speed cameras under external quasi-static tensile or dynamic impact loading conditions indicate that depending on the inclination angle, length and distribution pattern of cracks, fractures evolve considerably differently. Quasi-static load generally produces dynamic or quasi-static primary fracture with ensuing dynamic secondary retrograde fractures that are initiated at distant positions. Fractures can be arrested and jump easily, often resulting in clusters. Impact-related waves can induce primary fracture moving in both prograde and retrograde directions.

Fabrication of benzoyl chloride treated tiger-nut fiber reinforced insect repellent hybrid composite

An insect repellent composite containing tiger nut particulate fibre, waste low density polyethene (LDPE) and castor oil alkyd resin was fabricated. Canarium schweinfurthii gum was used as insect repellent compound and maleic anhydride as compatibilizer. The tiger nut chaff was subjected to benzoylation using benzoyl chloride to increase the fibre-matrix interaction. The compound and composition was then moulded with LDPE as dual matrices for excellent physico-mechanical properties (pressed for 5 min, 130 °C and 25 bar and cured). The 10 wt.% treated composite exhibited a minimum water absorption of ~ 0.085%, optimal chemical resistance for both acids (HCl and H2SO4) and bases (NaOH and KOH) and no effect on thickness. Density measurement showed the lowest value of ~ 0.0096 g/cm3 for the treated fibre composite. However, the tensile strength, flexural stress, hardness and impact load were improved up to 35.08 Mpa, 456.3 Mpa, 95 and 730 J/m respectively with treated composites. Insect repellent tests against termites and cockroaches show repellent activity with time intervals. FTIR and SEM analysis showed fibre modification achieved.

Investigation of Mechanical Properties of Silk and Epoxy Composite Materials

This research Investigates the new composite materials are fabricated of two or more materials raised. The fibers material from the sources of natural recycled materials provides certain benefits above synthetic strengthening material given that very less cost, equivalent strength, less density, and the slightest discarded difficulties. In the current experiments, silk and fiber-reinforced epoxy composite material is fabricated and the mechanical properties for the composite materials are assessed. New composite materials samples with the dissimilar fiber weight ratio were made utilizing the compression Molding processes with the pressure of 150 pa at a temperature of 80 °C. All samples were exposed to the mechanical test like a tensile test, impact loading, flexural hardness, and microscopy. The performing results are the maximum stress is 33.4MPa, elastic modulus for the new composite material is 1380 MPa, and hardness value is 20.64 Hv for the material resistance to scratch, SEM analysis of the microstructure of new composite materials with different angles of layers that are more strength use in industrial applications.

Dynamic fracture toughness of ultra‐high‐performance fiber‐reinforced concrete under impact tensile loading

AbstractThe fracture toughness and fracture energy of ultra‐high‐performance fiber‐reinforced concrete (UHPFRC) at both static and impact rates (43–92 s−1) were investigated using double‐edge‐notched tensile specimens. Two types of steel fiber, smooth and twisted fiber, were used in producing UHPFRC with different volume ratios of 0.5%, 1.0%, 1.5%, and 2%. The results indicated that UHPFRCs produced very high fracture resistance at impact rates, with first stress intensity factor (KIC) up to 3.995 MPa√m, critical stress intensity factor () up to 7.778 MPa√m, and fracture energy (GF) up to 86.867 KJ/m2, which were 2.5, 5.0, and 16.9 times higher than those of ultra‐high‐performance concrete, respectively. The was clearly sensitive to the applied loading rate, whereas the KIC and GF were not. Smooth fiber specimens exhibited not only higher and GF at impact rates but also higher dynamic increase factor than twisted fiber specimens. A minimum fiber volume content of 1% should be used in UHPFRC to provide a significant enhancement in crack resistance. The maximum value of UHPFRC crack velocity at impact rates was found to be 527 m/s by using a dynamic fracture mechanic model.

Manufacturing of 3D Printed Laminated Carbon Fibre Reinforced Nylon Composites: Impact Mechanics

This paper presents the manufacturing development of laminated Carbon Fibre Reinforced Thermoplastics Polymer (CFRTP) specimens, which show significant improvement of mechanical properties in comparison with existing thermoplastic composites. There is a need to improve structural performance of thermoplastic composites by using a fully integrated chopped and continuous carbon fibre bundle into a thermoplastic resin matrix in a laminated shape with various stacking sequences. The developed manufacturing technique is capable to print components with various fibre orientations, which is spotted as the novelty of this research. The CFRTP specimens were tested under quasi-static tensile and low-velocity impact loading to proof the improvement of mechanical performance in both static and dynamic applications. Our results indicate a significant improvement in impact resistance and energy absorption capability of CFRTP composites in comparison with existing thermoplastic composites.

Finite Element Analysis of Stress Wave Propagation in Adhesive Joints under Low Speed Impact Tensile Loadings

AbstractThe adhesive joints are suddenly disturbed by the impact loadings in industrial applications. The stress wave propagation and stress distribution in the single lap joint (SLJ) with aluminum alloy adherends and two types of epoxy adhesives under impact tensile loadings are analyzed with the finite element method (FEM) to simulate the drop weight test. The impact velocity is assumed below 2000 mm s−1 and the total impact history is 0.2 ms. The stress is observed throughout the middle plane in the overlap area. The stress wave propagation in the adhesive layer reveal obvious directivity and show the transformation from the elastic wave to the plastic wave. The equivalent Von‐Mises stress increases approximately linearly with the increase of impact energy. At different times, the equivalent Von‐Mises stress along the adhesive longitude present bimodal distribution, while the stress wave propagation characterizes the rising‐falling‐rising trend. The stress singularity area is around 3–5 mm from edges. The equivalent Von‐Mises stress of the transversal middle plane in the adhesive layer is sensitive to rupture with the symmetrical distribution. A damage sensitive area located 2.6 mm away from both edges. The upper interface of the adhesive layer may initiate failure under the low‐velocity impact.

Mechanical characterization of textile reinforced cementitious composites under impact tensile loading using the split Hopkinson tension bar

Strain-hardening cement-based composites (SHCC) reinforced additionally with continuous textile reinforcement exhibit a high tensile strength, ductility and low crack width up to failure localization, being suitable as strengthening layers on structural elements subject to impact loading. The quasi-static tensile properties of such composites are usually derived on long, planar specimens, as dictated by the geometry of the textile reinforcement and by the necessity of sufficient yarn anchorage. However, with regard to high strain rate testing in split Hopkinson bar systems, both the length and the planar shape of the textile reinforced specimen represent major drawbacks. This explains the lack of comprehensive investigations on the mechanical performance of textile reinforced cement-based composites from the perspective of material characterization. This paper presents two new configurations of a gravity-driven split Hopkinson tension bar (SHTB) purposefully developed for investigating the tensile behavior of such composites under strain/displacement rates in the range of impact loading. The first configuration is designed for uniaxial tension tests on planar textile reinforced composites. The planer specimens are attached to the input and output bars using special aluminum adapters. The influence of the adapters and of specimen geometry on wave propagation and dynamic stress equilibrium is discussed in detail based on the results of experimental and numerical investigation. Corresponding amendments to the traditional wave analysis and suitable evaluation methods are proposed for an accurate assessment of the material response. Additionally, a novel testing configuration for single-yarn pullout experiments is presented. This setup allows for a detailed description of the rate effects on the bond between textile yarns and cementitious matrix.

Tensile behavior of strain-hardening geopolymer composites (SHGC) under impact loading

Strain-hardening geopolymer composites (SHGC) exhibit remarkable ductility, crack control and high energy dissipation capacity when subject to quasi-static tensile loading. However, their mechanical performance under dynamic loading has not yet been explored. A comprehensive assessment of possible rate effects is required to facilitate a targeted material design for various practical applications. The article presents the results of an experimental investigation on the mechanical behavior of two types of SHGC under both quasi-static and impact tensile loading. The composites were reinforced with 2% of either short polyvinyl alcohol (PVA) fiber or ultra-high molecular-weight polyethylene (UHMWPE) fiber. The experiments were performed both at the composite scale and at the fiber level. The impact tests on the plain geopolymer matrix and SHGC were performed in a gravity-driven split-Hopkinson tension bar (SHTB) at strain rates of up to 300 s−1. The tests were accompanied by optical measurements to assess specimen deformation and multiple cracking by means of Digital Image Correlation (DIC). The dynamic fiber-matrix bond properties were investigated in a miniature split Hopkinson bar. Both under quasi-static tensile loading and impact tensile loading, the SHGC made with UHMWPE fibers exhibited superior mechanical performance compared to the composite made with PVA fibers. When comparing the impact tensile performance of SHGC with normal-strength SHCC from previous studies, SHGC demonstrated higher dynamic tensile strength and energy dissipation capacity, making SHGC promising for strengthening/prospective applications against highly dynamic actions.

A gravity-driven split Hopkinson tension bar for investigating quasi-ductile and strain-hardening cement-based composites under tensile impact loading

A gravitational split Hopkinson tension bar (SHTB) was developed with the goal of enabling an accurate characterization of the mechanical behavior of quasi-ductile cementitious composites in terms of force-deformation (stress-strain) curves under tensile impact loading. The design of the setup targeted additionally compact dimensions, simple operation, high adjustment flexibility, and low construction costs. The testing principle and the quality of the measurements were demonstrated by investigating a strain-hardening cement-based composite (SHCC) made with ultra-high molecular weight polyethylene (UHMWPE) fibers as well as its non-reinforced cementitious matrix at tensile strain rates of up to 200 s−1. The tensile impact tests were accompanied by high-speed optical measurements for subsequent analysis by means of Digital Image Correlation (DIC). In this way the mechanical measurements were double-checked, and the fracture processes in the specimens were analyzed in detail.

Mechanical Behaviour of ABS-Fused Filament Fabrication Compounds under Impact Tensile Loadings.

In the Fused Filament Fabrication (FFF) process, the part is built as a layer-by-layer deposition of a feedstock filament material. The continuous improvements of the FFF have changed the main purpose of this technique from rapid prototyping to a rapid manufacturing method. Then, it is fundamental to determine the material properties of FFF parts as a function of the service load. The impact loads and, in particular, a high strain rates tensile impact can be a critical issue in FFF part and, in general, for plastic materials. The aim of the present work is to characterise the mechanical behaviour of FFF parts under tensile impact loads. To this purpose, three different orientations (i.e., 0°, 45° and 90°) both single- and multilayer specimens, have been printed. Finally, the influence of the impact speed on the mechanical behaviour has also been tested under three different values of speed (3.78 m/s, 3.02 m/s and 2.67 m/s). The results show that the FFF parts are influenced by the raster orientation, confirming the orthotropic behaviour also under dynamic loads, while the variation of impact speed, on peak force and absorbed energy, is limited.

Transient Dynamic Stress Intensity Factor of FGM Plates Using the State Space and MLPG Methods

In this paper, a new effective method named state-space is extended and utilized to analyze FGM dynamic fracture problems, discretized by the meshless local Petrov–Galerkin method. Both the moving least square and the direct method have been applied to estimate the shape function and to impose the essential boundary conditions. The visibility criterion is used to simulate the displacement and stress field around the crack tip. Normalized dynamic stress intensity factors are calculated using the path-independent integral, J*, which is formulated for the non-homogeneous material. Two methods commonly used in solving such discretized problems, namely, the central difference method and the Newmark method, are compared with the proposed method. Both homogeneous and non-homogeneous (FGM) center-cracked plates under uniform tensile impact load are used to examine the accuracy and the computational time of the new method. The results of the implementation of these methods are compared with existent solutions. The results show that the state-space method saves substantial computational time for a given accuracy. The center-cracked plate made of FGM with two different material gradations (along and normal to the crack length) and four different FGM zones under the effect of uniform tensile impact load are considered, and the dynamic stress intensity factors are studied under the influence of various non-homogeneity ratios.

Performance of various strain-hardening cement-based composites (SHCC) subject to uniaxial impact tensile loading

Three different types of strain-hardening, cement-based composites (SHCC) as well as their constitutive cementitious matrices were investigated under uniaxial quasi-static and impact tensile loading. The normal-strength matrix was combined with polyvinyl-alcohol (PVA) fiber in one composite and with high-density polyethylene (HDPE) fiber in another. The third composite material consisted of high-strength matrix and HDPE fiber. A modified Hopkinson bar was used to assess the impact resistance of SHCC in terms of stress-strain relationships at displacement rates of 6m/s. The experiments were performed on specimens of two different lengths, for which, the strain rates were approximately 100s−1 and 200s−1, respectively.SHCC made of normal-strength matrix and PVA, the composite with considerable ductility under quasi-static loading, performed substantially worse at high strain rates than SHCC made with HDPE fiber. This could be traced back to the peculiar alteration of the fiber-matrix interaction depending on the type of fiber and corresponding bond properties (chemical bond in case of PVA fiber versus frictional bond in case of HDPE fiber). Furthermore, it was demonstrated that the effect of the increasing strain rates on the tensile performance of SHCC made with HDPE fibers can be controlled by adjusting the matrix composition, this being facilitated by the consistent and predictable strain rate sensitivity of the interfacial interaction between the HDPE fibers and the surrounding cement-based matrix.

Experimental and Numerical Study on Strengthening of Steel Members Subjected to Impact Loading Using Ultrahigh Modulus CFRP

AbstractCarbon fiber–reinforced polymers (CFRPs) are commonly used for strengthening steel and concrete structures, with different types of CFRP used for strengthening different structural elements. A number of studies have focused on strengthening of steel members using low and normal-modulus CFRP. However, there is a lack of understanding on the use of ultrahigh modulus (UHM) CFRP for strengthening steel structures under impact loading. This paper presents experimental and numerical investigations on the effect of high load rates on the ultimate joint capacity, failure mode, effective bond length, and strain distribution along the bond interface between CFRP and steel plates in double-strap joints. Two methods of capturing strain were used in this program: (1) Image correlation photogrammetry was used for specimens tested under quasi-static tensile load, and (2) foil strain gauges were used for specimens tested under impact tensile loading. UHM CFRP was used to strengthen the joints using epoxy. The res...

Investigation of composite filled hole coupons and lockbolt fastened joints under impact loading

Two different composite fastened configurations, i.e., the filled hole and the single-lap double-fastener joint, subjected to impact tensile loads, are investigated using efficient modelling techniques. The novel simulation methodology of the ‘stacked shell’ approach (or ‘2.5D’ approach) is exploited, in order to model the fastened composite coupons using the nonlinear explicit dynamics finite element code LS-DYNA. In the stacked shell approach, the composite plates are represented by discrete sublaminates of shell elements, which are tied together using interface elements with cohesive zone properties, resulting in a computationally efficient methodology of solving problems that involve significant inter-ply and intra-ply material failure. The numerical models are validated against relative experimental test data, derived from experiments which are performed within the investigated impact loading regime. The simulation results demonstrate that the models are capable to predict the onset of the damage, the failure modes and the load–displacement response of the fastened specimens with notable accuracy. In addition, the numerical investigation has shown limited loading rate sensitivity in terms of strength values for both of the examined configurations, while the lap joint samples illustrate pronounced changes in the final failure mode as the loading rate increases.

Effect of fiber properties and matrix composition on the tensile behavior of strain-hardening cement-based composites (SHCCs) subject to impact loading

The article at hand describes the behavior of high-strength and normal-strength strain-hardening cement-based composites (SHCCs) made of fine-grained matrix and high-density polyethylene fibers under quasi-static and impact tensile loading. The dynamic tension testing of unnotched and notched cylinders was performed using the Hopkinson bar at strain rates of around 150s−1. The responses of the materials under dynamic and quasi-static tensile loading were compared to the corresponding results for normal-strength SHCC made of polyvinyl-alcohol fibers as obtained in previous investigations. To explain the pronounced differences in rate effects on the material performance of various SHCC compositions, cracking pattern and fracture surface conditions were studied. Additionally, strain rate dependent changes in the mechanical behavior of individual fibers and in the fiber–matrix interfacial properties were deduced from single-fiber tension tests and fiber pullout tests, respectively. Altogether, the results obtained provide clear indications as to the decisive parameters for a purposeful material design of impact resistant types of SHCC for use in structural elements or protective overlays.

J0230101 衝撃引張負荷下の家兎膝蓋腱の断裂過程のAEモニタリングと高速度カメラによるその場観察

Rabbit patellar tendon-bone complex specimens were subjected to impact tensile load to simulate the sports accident. During the tests, microdamage initiation and accumulation process in tendon was monitored using acoustic emission (AE) technique. In addition, in-situ observation from vertical and horizontal directions using two high-speed cameras was carried out to determine the strain distribution. The stress increased monotonically to the ultimate tensile stress (UTS), which was significantly higher than the static tests. Despite of the extremely short time, a number of AE signals were detected continuously before the UTS. Furthermore, AE signals were emitted in the area where the local strain increased significantly in the strain distribution of the surface. It is then demonstrated that AE technique enables not only the detection of invisible microdamage but the identification of the damage location. It is worth nothing that the amplitudes of detected AE signals were much higher than static tests. Since AE amplitude corresponds to the magnitude of individual microdamage, it is suggested that larger magnitude of individual microdamage is initiated under impact tensile load. Consequently, it is demonstrated that AE technique has a possibility of clarifying the detailed rupture mechanism of tendon or ligament under impact load.

J1010203 強震動時の鋼材の材料強度と耐震裕度 : ひずみ速度依存性の影響評価に基づく一考察([J101-2]耐震・免震・制震 耐震(2))

Dynamic effect of impact loading such as seismic motion was researched in the viewpoint of seismic margin of steel structures. Impact fatigue tests were conducted from extremely low cycle to low cycle using cycle-loading test apparatus of impact-tensile load and the influence of dynamic strain on material strength of carbon steels. As the test results, the dynamic fatigue lives depended on strain amplitude not strain rate, suggesting the fatigue failure by seismic motion was not affected by strain rate. The strength for impact load includes viscosity stress caused by strain rate. Therefore, the test results and discussion suggested the viscosity stress corresponded to implicit seismic margin in the current design on the basis of stress.

Measurement of phase transformation properties under moderate impact tensile loading in a NiTi alloy

Pseudoelasticity is one of the main characteristics of shape memory alloys (SMAs), allowing them to recover their initial state after undergoing large deformation. This is due to the martensitic transformation (MT) occurring in the material, turning the austenitic phase into a stress-induced martensitic phase when a mechanical load is experienced. By conducting tests in quasi-static and dynamic ranges, studies have reported the strain rate dependence of the macroscopic behavior of SMAs. This paper investigates the influence of the strain rate applied to a NiTi SMA at the level of the MT, providing experimental data of the heterogeneous strain field occurring during quasi-static and dynamic tensile loading. Experiments were conducted at three different levels of prescribed velocity: 0.01mm/s, 1mm/s and 1000mm/s, using a classical loading machine for the quasi-static cases and a Split Hopkinson Tensile Bar (SHTB) for the dynamic cases. The observations of the heterogeneous strain field during the tests were made using a digital image correlation (DIC) technique which was validated by infrared thermography (IRT) measurements, considering that MT is exothermic. The analysis of the tests shows that the velocity of growth of the transformed zone is related to the applied velocity by a constant factor. Moreover, quantitative results about the strain level in the heterogeneous strain field are analysed. This study gives complementary results to the studies already made on MT in the quasi-static case, extending the observation by 103 to 105 times regarding the applied displacement rate.