Maximum Load Capability Research Articles

Bamboo-Inspired Structurally Efficient Materials with a Large Continuous Gradient.

Because of its light weight and high strength, bamboo is used in many applications around the world. Natural bamboo is built from fiber-reinforced material and exhibits a porous graded architecture that provides its remarkable mechanical performance. This porosity gradient is generated through the unique distribution of densified vascular bundles. Scientists and engineers have been trying to mimic this architecture for a very long time with much of the work focusing on the effect of fiber reinforcement. However, there still lacks quantitative studies on the role of pore gradient design on mechanical properties, in part because the fabrication of bamboo-inspired graded materials is challenging. Here, the steep and continuous porosity gradient through an ingenious cellular design in Moso bamboo is revealed. The effect of gradient design on the mechanical performance is systematically studied by using 3D-printed models. The results show that not only the magnitude of gradient but also its continuity have a significant effect. By introducing a continuous and large gradient, the maximum flexural load and energy absorption capability can be increased by 40% and 110% when comparing to the structure without gradient. These bamboo-inspired cellular architectures can offer efficient solutions for the design of damage tolerant engineering structures.

Dependency of Machine Efficiency on the Thermal Behavior of Induction Machines

The consideration of the thermal behavior of electric machines is becoming increasingly important in the machine design for electric vehicles due to the adaptation to more dynamic operating points compared to stationary applications. Whereas, the dependency of machine efficiency on thermal behavior is caused due to the impact of temperature on the resulting loss types. This leads to a shift of efficiency areas in the efficiency diagram of electric machines and has a significant impact on the maximum load capability and an impact on the cycle efficiency during operation, resulting in a reduction in the overall range of the electric vehicle. Therefore, this article aims at analyzing the thermal load limits of induction machines in regard to actual operation using measured driving data of battery electric vehicles. For this, a thermal model is implemented using MATLAB® and investigations to the sensitivity of model parameters as well as analysis of the continuous load capacity, thermal load and efficiency in driving cycles under changing boundary conditions are conducted.

A Transient-Enhanced Output-Capacitor-Free Low-Dropout Regulator With Dynamic Miller Compensation

A transient-enhanced output-capacitor-free low-dropout regulator (LDR) based on dynamic Miller compensation (DMC) is presented in this brief. By utilizing different Miller capacitors to compensate the LDR at different load ranges, the proposed DMC technique can extend the loop bandwidth and enhance the transient performances. The DMC scheme is simple and effective. A proof-of-concept LDR with DMC is designed in a 0.18- $\mu \text{m}$ CMOS process. It has a 100-mA maximum load capability with a quiescent current of $8.5~\mu \text{A}$ . Measurement results show that the output undershoot/overshoot and recovery time of the proposed LDR with DMC are only 38 mV/ $0.4~\mu \text{s}$ and 37 mV/ $1.22~\mu \text{s}$ when the load current changes between $100~\mu \text{A}$ and 100 mA, respectively, whereas they are 45 mV/ $1.3~\mu \text{s}$ and 200 mV/ $4.97~\mu \text{s}$ without DMC. Line transient responses are also significantly improved by the DMC technique.

Failure loads of all-ceramic cantilever fixed dental prostheses on post-restored abutment teeth: influence of the post presence and post position.

The influence of a fiber post-restored abutment tooth on the load capability of a three-unit zirconia framework cantilever fixed dental prosthesis (cFDP) was evaluated after simulated clinical function. Human lower sound premolars (n=64) were distributed, in equal numbers, to four experimental groups: two vital abutment teeth (group I; control); mesial abutment tooth post-restored (group II); distal abutment tooth post-restored (group III); and mesial and distal abutment teeth post-restored (group IV). All specimens received an adhesively luted three-unit cFDP of veneered zirconia. Simulated clinical function was performed by two subsequent sequences of thermal-cycling (2×3,000 cycles) and mechanical loading (1.2×106 load cycles from 0 to 50N) (TCML). Four specimens failed during TCML (one in each of groups I and IV and two in group II). The maximum load capability ranged from 365 to 538N and was not significantly different between groups. Specimens with post-restored abutments failed mainly because of abutment tooth fracture of the distal abutment. The presence or position of post-restored abutment teeth has no significant impact on load capability of all-ceramic three-unit cFDPs. The risk of tooth fracture of the distal abutment teeth of a cFDP was significantly increased when one abutment tooth, irrespective of its position, was post-and-core restored.

A Fully Integrated Low-Dropout Regulator With Differentiator-Based Active Zero Compensation

An area-efficient low-power fully integrated output-capacitorless low-dropout regulator (OCL-LDO) is presented in this paper. The three-stage OCL-LDO utilizes an embedded differentiator-based active zero compensation technique together with adaptive biasing. The proposed active zero compensation helps enhance the unity-gain bandwidth (UGB) of the regulator with very small silicon area and almost no extra current consumption. The UGB is therefore able to be maintained above 2.5 MHz even at a measured quiescent current of mere $1.6~\mu \text{A}$ . Adaptive bias is employed to further stabilize the circuit and extend the bandwidth extension as well as enhance the transient response. The chip area is 0.0021 mm2 with maximum load capability of 25 mA, which leads to a maximum current density of 11.9 A/mm2. The measured voltage spikes are below 40 mV for full-load transient responses, and the response time is about 1.2 ns. The voltage spikes of line transient responses are only 4 mV at full load. The measured full-load power-supply rejection is better than −44 dB up to 100 kHz.

Impact of simulated reduced alveolar bone support, increased tooth mobility, and distal post-supported, root-treated abutment tooth on load capability of all-ceramic zirconia-supported cantilever FDP.

The aim of this in vitro study was an analysis of the impact of simulated reduced alveolar bone support and post-restored, endodontically treated distal abutment tooth on load capability of all-ceramic zirconia-based cantilever-fixed dental prosthesis (CFDP). The roots of human lower sound premolars (n = 80) were divided into five experimental groups to be restored with all-ceramic zirconia-supported three-unit CFDP regarding bone loss (BL) relative to the cement-enamel junction (CEJ): 2mm below CEJ = 0% BL (control group), group 25% distal BL, group 50% distal BL, group 50% mesial and distal BL, and group 50% distal BL and adhesive post-supported restoration. Specimens were exposed to simulated clinical function by thermo-mechanical loading (6.000 cycles 5°-55°; 1.2 × 106 cycles 0-50N) and subsequent linear loading until failure. Tooth mobility increased significantly for groups with simulated bone loss (p < 0.001). Four specimens failed during thermal cycling and mechanical loading (TCML). The maximum load capability ranged from 350 to 569N, and did not differ significantly between experimental groups (p = 0.095). Groups with simulated bone loss revealed more tooth fractures at distal abutment teeth, whereas technical failures were more frequent in the control group (p = 0.024). Differences of alveolar bone support and respectively increased tooth mobility between mesial and distal abutments did not influence load capability. A distal adhesively post-and-core-supported, root-treated abutment tooth did not increase risk of three-unit CFDP failure. CFDPs are a treatment option used with caution when reduced alveolar bone support, increased tooth mobility, and distal post-supported, root-treated abutment teeth are involved.

Joining TWIP to TWIP and TWIP to aluminium: A comparative study between joining processes, joint properties and mechanical performance

In the present study, Resistance Spot Welding (RSW), Self-Piercing Riveting (SPR), Kerb Konus Riveting (KKR) and EJOWELD techniques were investigated for joining of TWIP steel sheets with one another and with Al. This is the first time the KKR and EJOWELD methods were compared to conventional joining methods The main focus was on the mechanical properties of similar joints produced between Zn-coated Fe–12Mn–1.5Al–1Si–0.5C Twinning Induced Plasticity (TWIP) steel and dissimilar joints between Zn-coated TWIP and Al 5754 or Al 6111 aluminium alloy sheet. The nugget solidification after fusion welding was evaluated through characterization with SEM-EBSD. In the case of RSW produced joints it was found that the joints with smaller grain size and larger orientation diversity exhibited larger maximum load capability. Regarding the joints produced with the EJOWELD method, grain size did not vary much compared with the base metal. Mechanical properties and the fracture behaviour of these joints were identified through the application of the lap shear method and failure modes. In the case of TWIP/TWIP combination, the results demonstrated that RSW samples exhibited the highest maximum load and corresponding elongation, while in dissimilar joining, SPR exhibited the largest maximum load. The EJOWELD method for the dissimilar joints showed similar mechanical properties to the SPR, in terms of maximum load, while KKR poorer properties. By comparing the mechanical properties of all the joints, it can be concluded that the primary factor of joint strength in RSW were the joining parameters (preweld and number of weld currents, welding time), while in the case of the other techniques it was the sheet strength.

Are self-adhesive resin cements suitable as core build-up materials? Analyses of maximum load capability, margin integrity, and physical properties.

The aim of the present study was to test a self-adhesive resin cement used as core build-up material in comparison to two commercially available core build-up materials. Forty human anterior teeth were endodontically treated and fiber post insertion (RelyX Fiber posts) and core build-ups were performed using two core build-up materials applied with an etch-and-rinse adhesive approach (Luxacore Dual-LC and Clearfil Core-CC) and an experimental self-adhesive resin cement (SAR) in two application modes (SAR Handmix and SAR Automix). Samples were subjected to thermo-mechanical loading. Margin integrity was determined using scanning electron microscopy (SEM), and maximum load capability (Fmax) was evaluated. Physical properties of the tested materials were also examined. Fmax was significantly affected by the core build-up material (p < 0.0005; one-way ANOVA). CC [481 (158) N] revealed significantly higher Fmax compared to LC [226 (80) N], SAR Hand [205 (115), and SAR Automix [197 (134) N] (p < 0.05; Tukey-B). The percentage of margin quality "continuous margin" in enamel after thermo-mechanical loading (TML) differed significantly among groups (p < 0.0005; Kruskal-Wallis); CC demonstrated a significantly higher percentage of margin quality "continuous margin" compared to the other groups. Physical properties were significantly affected by the different core materials (p < 0.0005; ANOVA); CC and LC demonstrated significantly higher flexural strength compared to both SAR groups as well as significantly higher water sorption of both SAR groups compared to CC and LC. Within the limitations of the present in vitro study, we conclude that the investigated experimental self-adhesive resin cement is not suitable as a core build-up material due to the lower maximum load capability, low margin quality, and the data of the mechanical properties. The investigated experimental self-adhesive resin cement cannot be recommended as a core build-up material.

Comparison between the RCF Performance of TiN- and TiO&lt;sub&gt;2&lt;/sub&gt;-Laser Coated Ti64 Bearings

The present work is a comparison between the rolling contact fatigue (RCF) of laser processed titanium bearings by using a scanning Nd:YAG Q-sw laser. TiN and TiO2 layers were produced on Ti6Al4V (Ti64) in a closed chamber in nitrogen and air atmosphere, respectively. The average thickness of the layers was 2 m in case of TiN and 0.8 m in case of TiO2. Both non-coated and coated bearings were RCF tested in under-water conditions and it was found that laser processing greatly improved their wear resistance and load capacity. Almost 50-fold and 20-fold increase in the wear resistance of the TiN and TiO2-coated bearings was observed after 7.7x106 cycles at a load of 150 N and 600 rpm. The mechanism responsible for this improvement is thought to be the 3-body-contact between the bearing elements and the small TiN and TiO2 debris, coming from the worn coating layers. The maximum load capability of the non-coated, TiN-coated and TiO2-coated bearings were 150 N, 200 N and 600 N. It is concluded that the higher load capacity of the TiO2 compared to the TiN coatings is due to its lower coefficient of friction.

Multi-level analysis of low-cost Z-pinned composite joints: Part 2: Joint behaviour

In the framework of the E-U program ALCAS (Advanced Low-Cost Aircraft Structure), a new Z-pinning technique was developed by EADS Innovation Works. This technology was used to manufacture low-cost Z-pinned junction demonstrators (L and T shaped specimens) typical of aeronautical structures. In order to understand load transfer mechanisms in this kind of assembly, a multi-level analysis was performed. In the first part of this study, tension and shear pin behaviour was investigated as well as pin pull-out from neat resin or laminate. An analytical model was proposed to predict the maximum load capability of a single pin for an insertion depth of less than 8 mm which correspond to the usual technology. Now, in this second part, we demonstrate that the behaviour of the junction under pull-out, shear and unfolding is globally homothetic to the mechanical behaviour of a pin. This study provides the basis for a pre-sizing methodology for Z-pinned junctions under complex loading.

Loading Standardization of Postendodontic Restorations In Vitro: Impact of Restorative Stage, Static Loading, and Dynamic Loading

The load capability of post-restored endodontically treated teeth (ETT) can be determined at different restorative stages. It was the aim of this study to compare the load capability of ETT at these stages. Maxillary central incisors were divided into 4 groups (n=10) and endodontically treated. Specimens were restored with: (I) only glass fiber posts (GFP); (II) GFP and composite build-up with 2 mm ferrule; (III and IV) with additional adhesively luted all-ceramic crowns. Group (I) to (III) were statically loaded, and group (IV) was exposed to thermomechanical loading (TML) and subsequent static loading. The lowest median load level of 73 N was determined for group (I). The maximum median load value of 331 N was found for group (III). The comparison of Fmax [N] of group (I), (II) and (III) revealed significant differences between the groups (p<0.001). The specimens of group (IV) failed at significantly lower load values (p<0.005) as similarly restored specimens of group (III) which were only statically loaded. The stage of restoration and TML loading prior to static loading had a significant impact on fracture patterns (p=0.006). Every additional restorative step torwards a final crown-restored ETT significantly increased the load capability. TML prior to load-to-fracture testing of the complete restorative complex, ie. post, core and crown, significantly decreased maximum load capability.

Focus on nanoscience and nanotechnology

Focus on nanoscience and nanotechnology

Influence of type of luting cement used with all-ceramic crowns on load capability of post-restored endodontically treated maxillary central incisors

Adhesive luting of the final restorations is supposed to support the overall strength of post-endodontically restored teeth. For evaluating adhesive vs conventional cementation, the load capability of adhesively restored endodontically treated teeth (ETT) with glass fibre-reinforced composite posts (GFRCP), resin composite cores and all-ceramic crowns was determined. Thirty-two caries-free human upper, central incisors were randomly assigned to four groups, endodontically treated and cut 2 mm above the cemento-enamel junction. All teeth were restored with GFRCP, composite core build-ups and all-ceramic crowns. All-ceramic crowns were cemented with zinc phosphate cement (I), glass ionomer cement (II), and a self-adhesive resin cement (III and IV). After thermo-mechanical loading, the specimens were loaded to fracture. Maximum load capability F(max) and fracture patterns were compared using non-parametric statistics. Median values for the maximum load capability F(max) (minimum/maximum) in [N] were: I = 503 (416/1,038), II = 442 (369/711), III = 502 (326/561) and IV = 518 (416/652). No statistically significant differences were found for F(max) (p = 0.761) and fracture patterns (p = 0.094) between the experimental groups. The type of cementation of all-ceramic crowns, whether self-adhesive or conventional, appears to have no impact on the load capability of ETT restored with GFRCP and composite core build-ups.

A theoretical and experimental investigation of a family of minimum-weight simply-supported beams

Space and force diagrams are presented for a family of simply-supported minimum-weight beam structures. The analytical methods, used to determine volume and displacements for a structure with different strength in tension and compression, are reviewed using the simplest circular arc beam example. The full design of a non-trivial symmetrical beam is described. The use of power series solutions and a matrix operator numerical method, developed for plane-strain slip-line field theory, are described to determine the beam layouts. The results of testing beam models, manufactured using both laser free-form sintering of nylon powder and CNC milling of aluminum alloy plate, are compared to the theoretical predictions of stiffness and maximum load capability. The theoretical predictions are shown to provide excellent agreement with both the isotropic aluminum test structure, and with the strongly bi-modulus nylon test structures.

J-R Curves From Circumferentially Through-Wall-Cracked Pipe Tests Subjected to Combined Bending and Tension—Part I: Theory and Numerical Simulation

One of the key aspects in leak-before-break analyses is to predict the maximum load-carrying capacity of a circumferentially cracked pipe. Such analyses require the fracture resistance of the material using the J-integral parameter, typically using small-scale laboratory specimens, such as compact tension, C(T), or three-point bend specimens. To evaluate the similitude between the laboratory specimens and a circumferentially through-wall-cracked pipe, the toughness can be evaluated directly from the pipe using an analysis typically called an η-factor approach. The fracture resistance from the pipe tests can then be compared to laboratory specimen toughness values to assess similitude issues. Additionally, several analysis methods (i.e., LBB.NRC, LBB.ENG, LBB.GE, etc.) that predict maximum load capability of through-wall-cracked pipes have η-factor analyses embedded in them. Hence, the evaluation of the J-R curve accuracy or consistency with small-scale specimens is a verification of one step in such predictive analyses. This paper presents extensions to the earlier η-factor solutions for circumferentially through-wall-cracked pipes where the previous analyses were for cracks in pipes under either pure bending or pure tension. The improvements investigated account for loading under combined bending and tension due to internal pressure. The application of these methods to full-scale pipe tests is presented in Part II (Miura and Wilkowski, 1998) of this paper.

Direct Methods of Stability Analysis in Dynamic Security Assessment

Direct methods of stability analysis have been intensely investigated over the past two decades and are now found practicable in obtaining accurate critical breaker clearing times for a given fault. Obtaining this information on-line is only an indirect way of ascertaining robustness of the system. In this paper we propose to convert this information into more realistic criteria such as simultaneous interchange capability (SIC) or maximum load capability (LSC) of the system subject to the system surviving thp contingencies in a transiently stable manner. A fast transient stability algorithm combined with sensitivity of the energy margin to the LSC or SIC is proposed. Verification of the methodology on a 1O-machine system lends confidence in this technique as a tool for dynamic security assessment.

A tensile creep-testing apparatus for ceramic materials using simple knife-edge universal joints

A simple method of long-term tensile creep-testing of ceramic materials is described, employing frictionless knife-edge universal joints and a gripping system which minimizes nonaxialities. The apparatus has a maximum constant load capability of 100 kg and was designed for use up to 1000 degrees C to test glass-ceramic materials. Some results are given which illustrate the reproducibility of the method, and an estimation of the errors involved in strain measurement is made.