Cyclic Bending Loads Research Articles

Reliability and Failure Analysis of Lead-Free Solder Joints for PBGA Package Under a Cyclic Bending Load

Nowadays, interest in the bending reliability of ball grid array packages has increased with the increase in mobile devices. Initially, bending tests were conducted to certify the safety of an electronic package during the manufacturing and shipping processes. But recently, the purpose of the bending test has changed: cyclic bending tests are being used to evaluate the electronic package's endurance against handling damage such as bending, twisting and key pressure. Furthermore, the bending test is being adopted as an alternative to a drop test. In this study, a four-point cyclic bending test was performed under various loading levels to investigate the fatigue behavior of solder joints with chemical compositions of 95.5Sn4.0Ag0.5Cu and 63Sn37Pb. It was found that the lead-free solder has a longer fatigue life than the lead-contained solder when the applied load is low. A finite element analysis (FEA) with plasticity and creep constitutive equations was conducted because there are no suitable sensors to measure stress and strain of solder ball joints directly. From the analysis results, it was found that the inelastic energy dissipation could be used as a good damage parameter. Also, from the inspection of the failure site and the FEA, it was found that the fatigue crack initiated at the exterior solder joints and propagated into the inner solder joints.

OS0616 曲げモーメント作用下における骨梁内間質液流れの多孔質弾性解析(OS06-04 力学特性の発現機構,OS06 微視構造を有する材料の変形と破壊(2))

OS0616 曲げモーメント作用下における骨梁内間質液流れの多孔質弾性解析(OS06-04 力学特性の発現機構,OS06 微視構造を有する材料の変形と破壊(2))

Static and Fatigue Analysis of a Hybrid Joint Part for the Tilting Car Body

Fatigue fracture behavior of a hybrid joint part for the tilting car body was evaluated in comparison to the case of static fracture. The specimens of hybrid joint part applied in the real tilting car body were fabricated for the bending test. Characteristic fracture behaviors of hybrid joint part specimens under cyclic loads were obviously different from the case under static loads. Static bending load caused the shear deformation and fracture in the honeycomb core region, while cyclic bending load did the delamination along the interface between composite skin and honeycomb core layers as well as the fracture of welded joint part. Experimental results obtained by static and fatigue tests were reflected in modifications of design parameters of the hybrid joint structure in the real tilting car body.

Isothermal Cyclic Bend Fatigue Test Method for Lead-Free Solder Joints

Isothermal three-point and four-point cyclic bend fatigue test methods have been developed for Sn–Ag–Cu solder joints. Reported bend tests from the literature were conducted at room temperature (25°C) and there is lack of data for lead-free solder joints. In this study, very-thin quad flat no-lead (VQFN) assembly with Sn–Ag–Cu lead-free solder was tested under three-point and four-point cyclic bending loads at both room temperature (25°C) and high temperature (125°C). The correlation between three-point and four-point bend tests was developed. Two different board surface finishes of electroless Ni and immersion gold (ENIG) and organic solderability preservatives (OSP) were investigated. Bending fatigue resistance of VQFN with OSP finish is slightly better than ENIG finish case. The acceleration factor of failure at high temperature (125°C) is higher than that at room temperature (25°C). Finite element analysis modeling and simulation were performed for different test conditions to investigate the solder joint stress-strain behavior. Volume-averaged energy density was used as a fatigue damage parameter and energy-based bending fatigue models were developed for VQFN with Sn–Ag–Cu solder joint under cyclic bending load at both 25°C and 125°C.

Seismic Performance of Square Reinforced Concrete Columns under Combined Cyclic Flexural and Torsional Loadings

This article presents an experimental investigation on the behavior of reinforced concrete cantilevered columns subjected to combined cyclic bending and torsional loading. Seven columnar specimens with the same structural properties were tested under various loading conditions: cyclic torsion, cyclic uniaxial bending, and combined cyclic torsion and cyclic uniaxial bending with and without a constant axial compression force. Several combinations of cyclic bending and cyclic torsion expressed in terms of the rotation–drift ratio r were applied to study the interaction between torsion and flexural capacity of columns. The result reveals that the flexural capacity decreases and the damage tends to occur upward outside the flexural plastic hinge region as the level of applied cyclic torsion increases. An empirical model for the flexural and torsional hysteretic behavior is proposed based on the experimental result.

Development of a new device to perform torsional ultrasonic fatigue testing

The interest in gaining experimental knowledge on fatigue strength of materials over 10 9 cycles is rapidly increasing as evidenced for the large amount of investigations on this subject presented at the last very high cycle fatigue meeting (VHCF-3), held on September 2004. Most of the fatigue results presented at this conference were obtained under tension-compression, rotating bending, flexion and bending cyclic loading (some attaining 10 10 cycles), using ultrasonic devices whose design was based on the natural frequency principles. In general, very little literature concerning the metallic alloys behavior under torsion cyclic loading using ultrasonic is available; however, in order to perform an accurate component design under multi-axial loading and VHCF, the material behavior under torsion cyclic loading is required. This investigation presents the development of a new mechanical device for testing and characterizing metallic alloys in the range of 10 9–10 10 cycles in torsional cyclic loading and the first experimental results for medium carbon steel (38MnSV5S). The new device was designed to excite the components under testing with pure torsional vibration mode at a frequency of 20 kHz.

Fatigue tests and design of thin CHS-plate T-joints under cyclic in-plane bending

A review of existing fatigue design guidelines has been undertaken and shows that there are no fatigue design recommendations for circular hollow section-to-plate T-joints subjected to in-plane bending. This paper therefore reports on the high cycle fatigue behaviour of welded thin-walled circular hollow section (CHS) tubes of thicknesses less than 4 mm that are fillet-welded onto a plate to form a base plate moment connection. The resultant thin CHS-Plate T-joints are subjected to cyclic in-plane bending load to determine their fatigue strength at different stress ranges. The S–N data from the failed thin CHS-Plate T-joints is analysed using the least-squares method of statistical analysis to obtain a design S–N curve. The derived design S–N curve for the thin CHS-Plate T-joints is compared to existing design S–N curves and also that of square hollow section (SHS)-to-plate T-joints under in-plane bending in current fatigue design guidelines. The thin CHS-Plate T-joints are found to have a better fatigue strength compared to the existing S–N curve for SHS-Plate T-joints under in-plane bending. An appropriate design S–N curve from the group of existing design S–N curves is adopted for the design of thin CHS-Plate T-joints.

틸팅차량용 차체의 Hybrid 복합재 접합체결부의 정적 및 피로 파괴 평가

Fatigue fracture behavior of a hybrid bolted joint was evaluated in comparison to the case of static fracture. Two kinds of specimens were fabricated for the mechanical tests; a hybrid bolted joint specimen for the shear test and a hybrid joint part specimen applied in the real tilting car body for the bending test. Characteristic fracture behaviors of those specimens under cyclic loads were obviously different from the case under static loads. For the hybrid bolted joint specimen, static shear loading caused the fracture of the bolt body itself in a pure shear mode, whereas cyclic shear loading brought about the fracture at the site of local tensile stress concentration. For the hybrid joint part specimen, static bend loading caused the shear deformation and fracture in the honeycomb core region, while cyclic bend loading did the delamination along the interface between composite skin and honeycomb core layers as well as the fracture of welded joint part. Experimental results obtained by static and fatigue tests were reflected in modifications of design parameters of the hybrid joint structure in the real tilting car body.

OS4-3-2 Flexural Rigidity Evolvement RC Beams Strengthened with Carbon Fiber Laminate under Cyclic Bending Loads

The flexural rigidity evolvement of RC beams strengthened with carbon fiber laminate under cyclic bending loads is investigated in this paper. In the fatigue experiment, 14 reinforced concrete beams strengthened with carbon fiber laminates (CFL) are divided into three groups according to the peak stress applied on the CFL, and tested under bending loads with constant amplitude. The results show that: (1) the flexural rigidity development follows a rapid decrease phase, a uniform decrease phase, and a rapid decrease until failure phase; (2) there is linear relationship between flexural rigidity and normalizing fatigue cycles in the uniform decrease phase. Moreover, if the stress level is not beyond the main reinforcement yield stress, the flexural rigidity evolvement rules are independent on the stress levels.

Shakedown Limits of a 90-Degree Pipe Bend Using Small and Large Displacement Formulations

In this paper the shakedown limit load is determined for a long radius 90-deg pipe bend using two different techniques. The first technique is a simplified technique which utilizes small displacement formulation and elastic–perfectly plastic material model. The second technique is an iterative based technique which uses the same elastic–perfectly plastic material model, but incorporates large displacement effects accounting for geometric nonlinearity. Both techniques use the finite element method for analysis. The pipe bend is subjected to constant internal pressure magnitudes and cyclic bending moments. The cyclic bending loading includes three different loading patterns, namely, in-plane closing, in-plane opening, and out-of-plane bending. The simplified technique determines the shakedown limit load (moment) without the need to perform full cyclic loading simulations or conventional iterative elastic techniques. Instead, the shakedown limit moment is determined by performing two analyses, namely, an elastic analysis and an elastic–plastic analysis. By extracting the results of the two analyses, the shakedown limit moment is determined through the calculation of the residual stresses developed in the pipe bend. The iterative large displacement technique determines the shakedown limit moment in an iterative manner by performing a series of full elastic–plastic cyclic loading simulations. The shakedown limit moment output by the simplified technique (small displacement) is used by the iterative large displacement technique as an initial iterative value. The iterations proceed until an applied moment guarantees a structure developed residual stress, at load removal, equal to or slightly less than the material yield strength. The shakedown limit moments output by both techniques are used to generate shakedown diagrams of the pipe bend for a spectrum of constant internal pressure magnitudes for the three loading patterns stated earlier. The maximum moment carrying capacity (limit moment) the pipe bend can withstand and the elastic limit are also determined and imposed on the shakedown diagram of the pipe bend. Comparison between the shakedown diagrams generated by the two techniques, for the three loading patterns, is presented.

Stability of Residual Stresses of Deep Rolled Sintered Iron at Quasistatic and Cyclic Loading

In the work presented here the residual stress states of sintered iron (ASC 100.29) were studied after mechanical surface treatments. This included the investigation of the stability of compressive residual stresses of deep rolled sintered iron at different angles relative to the rolling direction at quasistatic and cyclic bending loading. An increase of the compressive residual stress in the transversal deep rolling direction at fatigue loading was found and will be discussed in this presentation.

Fatigue life prediction of sandwich composite materials under flexural tests using a Bayesian trained artificial neural network

The authors discuss the use of an artificial neural network (ANN) to estimate fatigue lifetime of a sandwich composite material structure subjected to cyclic three-point bending loads. A total of 27 samples (three different loading levels for nine samples each) were investigated to provide training, validation and testing data for a series of multi-layer perceptron ANNs. The networks were implemented using both conventional maximum likelihood and Bayesian evidence based training algorithms. It was found that the Bayesian evidence based approach provided a superior and smoother fit to the experimental data. Completely independent fatigue tests were conducted at intermediate levels of loading to evaluate the capacity of the fitted ANN model to interpolate to previously unseen regions of data. Excellent agreement was obtained between the model predicted outputs and the new experimental data. The capability and estimation of predication error when using the Bayesian technique is discussed along with the application of the model to generate classical S– N lifetime curves.

Biomechanical Analysis of Blade Plate Versus Locking Plate Fixation for a Proximal Humerus Fracture: Comparison Using Cadaveric and Synthetic Humeri

To compare the mechanical stability of a fixed-angle blade plate with that of a locking plate in a cadaveric proximal humerus fracture-fixation model subjected to cyclic loading. A secondary objective was to evaluate whether the use of synthetic humerus specimens would replicate significant differences found during cadaveric tests. Mechanical evaluation of constructs in bending and torsion. Biomechanical laboratory in an academic medical center. Simulated humeral neck fractures (Orthopaedic Trauma Association (OTA) classification 11A3), in matched-pair cadaveric and synthetic specimens underwent fixation using either a 3.5-mm, 90-degree cannulated LC-Angled Blade Plate or a 3.5-mm LCP Proximal Humerus Locking Plate. Cadaveric specimen constructs were cyclically loaded in bending and torsion; synthetic specimens were tested in torsion. Humeral shaft-bending displacements and angular rotations for respective cyclic bending loads and axial torques were recorded and compared at repeated cyclic intervals to evaluate construct loosening. Locking-plate constructs exhibited significantly less loosening than blade-plate constructs for torsional loading in cadaveric specimens (P = 0.036). The two types of constructs performed similarly for torsional loading in synthetic specimens (P = 0.100). Under cyclic, closed-bending load conditions in which the plates served as tension members, both types of constructs performed similarly in cadaveric specimens (P = 0.079). For simulated humeral neck fractures subjected to cyclic loading, locking-plate constructs demonstrated significantly greater torsional stability and similar bending stability to blade plates in a cadaveric specimen model. In contrast, these same constructs performed similarly with torsional loading when using synthetic humerus specimens. These results indicate potential advantages for locking-plate fixation. They also indicate that the synthetic specimens tested may not be appropriate for evaluating fixation stability in the humeral head, where cancellous bone fixation predominates.

Phased Array Ultrasonic Measurement of Fatigue Crack Growth Profiles in Stainless Steel Pipes

This paper reports experimental sizing of fatigue crack profiles that are initiated from artificially made circumferential starter notches in stainless steel pipes of 169mm outer diameter and 14.33mm thickness, which were subjected to cyclic bending loads in a four point bending load arrangement using two nondestractive evaluation (NDE) methods: (a) phased array ultrasonic technique and (b) alternating current potential drop technique. The crack growth estimated using the two NDE techniques were compared with the beach marks that were present in the fracture surface. A simulation study using the ray tracing method was carried out to model the ultrasonic wave propagation in the test specimen, and the results were compared with the experimental results.

Performance characteristics of heater elements made of carbon fibres

The optimum concentration of a solution of adhesive required for impregnating CF is 35±5%, which corresponds to a 45±5% content in the fibre. An electric current is transmitted in CF due to the relatively low resistance of the fibre filaments and according to a “chain” scheme. The change in the strength of CF under the effect of cyclic double bending and preliminary loading was determined. The characteristics of the increase in the electrical resistance as a function of the number of double bending cycles, correlated with breaking of the CF filaments and a decrease in the contacts between them, were established.

On the redesign of a shear pin under cyclic bending loads

An integrated motor and gearbox package drives a 3.9 kN flocculator train at a water filtration plant. The 4–20 rpm output shaft turns the flocculators at 1–5 rpm. Mounted on this shaft is a torque limiting coupling, utilizing a SAE 1040 steel shear pin. Analogous to a fuse in an electrical circuit, this shear pin fails if the flocculator paddles jam, thus protecting the equipment from overload. With the current design, a shear pin only last about one week. Analysis suggests that cyclic fatigue, caused by misalignment between driving and driven coupling elements, causes premature pin failure. A redesigned shear pin made from PH 13-8 Mo stainless steel, processed to improve fatigue resistance, is described.

Testing and life prediction for composite rotor hub flexbeams

A summary of several studies of delamination in tapered composite laminates with internal ply-drops is presented. Initial studies used 2D FE models to calculate interlaminar stresses at the ply-ending locations in linear tapered laminates under tension loading. Strain energy release rates for delamination in these laminates indicated that delamination would likely start at the juncture of the tapered and thin regions and grow unstably in both directions. Tests of glass/epoxy and graphite/epoxy linear tapered laminates under axial tension delaminated as predicted. Nonlinear tapered specimens were cut from a full-size helicopter rotor hub and were tested under combined constant axial tension and cyclic transverse bending loading to simulate the loading experienced by a rotor hub flexbeam in flight. For all the tested specimens, delamination began at the tip of the outermost dropped-ply group and grew first toward the tapered region. A 2D FE model was created that duplicated the test flexbeam layup, geometry, and loading. Surface strains calculated by the model agreed very closely with the measured surface strains in the specimens. The delamination patterns observed in the tests were simulated in the model by releasing pairs of multi-point constraints (MPCs) along those interfaces. Strain energy release rates associated with the delamination growth were calculated for several configurations and using two different FE analysis codes. Calculations from the codes agreed very closely. The strain energy release rate results were used with material characterization data to predict fatigue delamination onset lives for nonlinear tapered flexbeams with two different ply-dropping schemes. The predicted curves agreed well with the test data for each case studied.

Effects of Simulated Seismic Loading on LBB Assessment of High Energy Piping

The current Leak Before Break (LBB) assessment is based primarily on the monotonic fracture tearing instability. In it the maximum design accident load is compared with the fracture-tearing resistance load. The effect of cyclic loading has not been generally considered in the fracture assessment of nuclear power plant piping. It is a well-known fact that reversible cyclic loading decreases the fracture resistance of the material, which leads to increased crack growth. Indian nuclear power reactors consider Operational-Basis-Earthquake (OBE) and Safe-Shutdown-Earthquake (SSE) events in the design of various structures, systems, and components. Keeping this in view a series of cyclic tearing tests have been conducted on straight pipes, made of ASTM SA333 Gr.6 carbon steel. This is the material of primary heat transport (PHT) piping material of Indian Pressurized Heavy Water Reactors (PHWR). In this series 13 tests have been carried out circumferentially through wall cracked seamless and circumferential seam welded straight pipes under reversible cyclic bending loading. All the tests have been conducted under quasistatic, i.e., slow loading rates and dynamic inertia effects are not considered. The cyclic test results have been compared with the corresponding monotonic pipe fracture test results. These test results and its comparison with corresponding monotonic tearing clearly illustrate the need of addressing the reduction in apparent fracture toughness of material under reversible cyclic loading and the safe number of load cycles in the LBB assessment.

A Simple Fatigue Life Model for Three-dimensional Fiber-Polymer Composites

A simple model is proposed for predicting the fatigue life of three-dimensional (3D) fiber-polymer composite materials for certain cyclic load conditions. The fatigue life can be easily calculated using the model with three empirically determined constants: (i) the ultimate strength of the 3D composite, (ii) the ultimate strength of the two-dimensional (2D) laminate, which is identical in every respect to the 3D composite (e.g., same fiber layup pattern, fiber volume content) except for the through-thickness reinforcement, and (iii) the slope parameter (m) of the fatigue-life (S-log N) curve for the 2D laminate. It is shown that the S-log N curves for stitched composites under cyclic tension-tension and compression-compression loading and for z-pinned composites under cyclic bending loading can be accurately predicted using this model. This model can also approximate the tensile fatigue life of composite lap joints reinforced by stitches or z-pins. However, the model is not reliable in predicting the fatigue life of 3D composites in all cases. It is only accurate when the fatigue damage mechanisms and failure mode of the 3D composite are not altered significantly by the through-thickness reinforcement. Consequently, a limitation of the model is that a priori knowledge of the fatigue damage process of the 3D composite is needed before it can be used with confidence to predict fatigue life. This problem is exasperated by the paucity of information available on the fatigue mechanisms of many types of 3D composites. Until this problem is resolved, the model should only be applied to those types of 3D composites in which their fatigue processes have been determined.

Crack propagation paths in layered, graded composites

Layered, graded material structures exhibit anisotropies in elastic properties and failure resistance that can strongly influence the propagation of cracks, and hence overall structural integrity. This study examines the influences on propagation trajectory for cracks initially oriented parallel to the layers in layered, graded alumina-epoxy composites, produced experimentally by infiltration of layered porous alumina bodies. Notched specimens were tested under monotonic and cyclic bending loading. Finite element (FE) modelling was used to predict crack-tip stress fields and crack propagation paths. Measured initial crack deflection angles agreed with predictions from FE results, and observations from phase-shifted Moiré interferometry. Crack propagation paths showed good agreement with FE predictions, except when cracks were influenced by interfaces between layers. Influences of elastic property gradient, microstructural heterogeneity and toughness anisotropy at interfaces are addressed, and the implications for structural reliability of layered structures are discussed.