Probability Of Local Failure Research Articles

PIK3CA Mutation is Associated With Increased Local Failure in Lung Stereotactic Body Radiation Therapy

Hyperactivation of the phosphatidylinositol-3-kinase (PI3K) pathway has been associated with radioresistance. It is unclear whether such mutations also confer suboptimal local control for patients who receive lung stereotactic body radiation therapy (SBRT). Our objective was to examine whether mutations in the EGFR/AKT/PIK3CA signaling pathway are associated with local failure (LF) after lung SBRT. We retrospectively reviewed 168 patients who underwent SBRT to primary or metastatic lung lesions from 2007-2015 for whom molecular testing data was available for EGFR, AKT, and PIK3CA genes. For tumors of lung origin (n = 156), molecular testing data was included from the lung tumor. For metastatic tumors to the lung (n = 12), molecular testing data from either a primary or metastatic tumor site was used. Association between clinical factors, including molecular mutation status, and LF was evaluated with Cox regression analysis. The Kaplan-Meier method was used to assess differences in LF rates based on PIK3CA mutation status. The most common histology was adenocarcinoma (92%) among all tumors. Six patients (4%) had PIK3CA mutation, 36 patients (21%) had EGFR mutation, and one patient (0.6%) had AKT mutation. Median lesion size was 2.0 cm (range, 0.6–5.6 cm), median dose was 48 Gy (range 30–70 Gy), and median number of fractions was 4 (range, 3–10). Median follow-up was 21 months (range, 0.2–70 months). LF was observed for 16 patients (10%). On univariate analysis, PIK3CA mutation presence was associated with LF (HR 11.0 [95% CI 2.3-52.6], P = 0.003), while tumor histology (adenocarcinoma vs. other), tumor size (≤2 cm vs. >2 cm), primary tumor site (lung vs. other), BED (<100 Gy versus ≥100 Gy) and EGFR mutation presence were not. At one year, probability of LF in lesions with PIK3CA mutations was 25.0% vs. 3.1% in lesions without mutations (P < 0.001). Lesions with PIK3CA mutations were associated with a decreased time to LF (mean 17.4 months [95% CI 11.1-12.8 months]) compared to those without PIK3CA mutation (mean 61.3 months [95% CI 57.0-65.7 months]). Although the number of patients affected was small, PIK3CA mutation was significantly associated with a much higher risk of LF in patients undergoing lung SBRT. This association has not previously been reported for lung SBRT and indicates the need for further validation and study.

Local Control After Stereotactic Body Radiation Therapy for Early-Stage Non-Small Cell Lung Cancer: A Tale of 2 Schedules?

Stereotactic body radiation therapy (SBRT) for early-stage (T1-3, N0, and M0) non-small cell lung cancer (NSCLC) generally yields excellent local control rates. The optimal dose and fractionation schedule remains unknown, especially for the treatment of central tumors. At our institution, we typically treat early-stage NSCLC patients with 10-11 Gy x 5 fractions for central tumors and 18-20 Gy x 3 fractions for non-central tumors. We present our institutional experience with SBRT for early-stage NSCLC and examine if local control rates vary with SBRT schedule. We identified patients who were treated with SBRT for early-stage NSCLC between September 2009 and May 2015. Patients with T1-3, N0, M0 tumors were eligible. Patients with more advanced disease, lung nodules attributed to other diagnoses, or missing follow-up data were excluded. Actuarial local control rates and freedom from progression rates for the entire cohort and for subsets treated with 10-11 Gy x 5 (Schedule A) and 18-20 Gy x 3 (Schedule B) were calculated using the Kaplan-Meier method. Comparisons were made using log-rank testing. Toxicity grading was performed using Common Terminology Criteria for Adverse Events (CTCAE) or Radiation Therapy Oncology Group (RTOG) criteria. Sixty-one patients met all inclusion criteria. With a median follow-up of 15.0 months, four local failures were observed, and fifteen patients developed progressive disease. Actuarial local control rates at 1 and 2 years were 98% and 92%, respectively. Four out of 29 patients receiving Schedule A experienced local failure, compared to 0 out of 32 patients receiving Schedule B. The 2-year actuarial local control rate for patients treated with Schedule A was 83%, compared to 100% for patients treated with Schedule B (log-rank P=0.040). Actuarial freedom from progression rates at one and two years were 88% and 67%, respectively. The 2-year actuarial freedom from progression rate for patients treated with Schedule A was 64%, compared to 70% for patients treated with Schedule B (log-rank P=0.079). Mean tumor diameter was 2.5 cm for tumors treated with Schedule A and 1.9 cm for tumors treated with Schedule B (unpaired t-test P=0.011). No grade 3 or higher acute or late toxicities were observed. SBRT for early-stage NSCLC yields excellent rates of local control, with progression most often occurring at regional and/or distant sites. 10-11 Gy x 5 schedule and increased tumor size were associated with increased probability of local failure. Additional studies with higher numbers of local failures will be necessary to fully characterize the interplay between SBRT schedule and/or tumor size as predictive factors.

Probabilistic landslide risk assessment of a historic and cultural site on the north slope of Lishan Mountain, Xian, China

This paper introduces the statistical methods and application for the quantitative analysis of a site-specific landslide risk on the north slope of Lishan Mountain which is regarded being in an active state that could become a disastrous loess landslide. Based on the theory of probability statistics (Monte Carlo statistical methods) and the slope failure mechanical model, the overall failure probability and the local failure probabilities of the Lishan landslide were calculated. The results of the failure probability and stability analysis showed that the northern slope of Lishan Mountain is highly prone to lose stability during seasonal intense rainfall, whereas it is stable but still exhibits failure probability under arid conditions. The analysis of the safety margin and local failure probability evidenced that the upper part of the slope is less stable than the lower part. Under the intense rainfall condition, the local failure probability and hazard of local unstable failure of the slope will increase. According to the calculation results, it is deduced that the landslide on the north of Lishan Mountain will be a gradual process evolving from the local slope failure to an overall unstable failure.

Probabilistic assessment of local scour in bridge piers under changing environmental conditions

Scour is one of the most widespread causes of bridge failure worldwide. The magnitude of the river flow at the bridge location is a key factor which directly affects the scour hole depth. Climate change may cause changes in the flow characteristics in a river due to changes in the precipitation patterns and catchment characteristics. In this paper, statistical analysis of the expected maximum annual flow of rivers is combined with the Monte Carlo simulation to estimate the probability of local scour failure. Climate change is assumed to manifest itself through gradual changes in the statistical characteristics of the expected maximum annual flow distributions. Results are presented from a case study using a bridge in the UK, which revealed that a time-dependent increase in the mean of the expected maximum annual flow has a more pronounced effect on scour performance as compared to an increase of its variability alone. Amongst the cases examined, however, the most adverse effect on local scour performance is observed from the simultaneous increase in both mean and variability of the expected maximum annual flow. The results also highlighted the significance of the foundation depth and local scour model parameter in relation to the changing flow characteristics.

Detection Performance in Balanced Binary Relay Trees With Node and Link Failures

We study the distributed detection problem in the context of a balanced binary relay tree, where the leaves of the tree correspond to <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">N</i> identical and independent sensors generating binary messages. The root of the tree is a fusion center making an overall decision. Every other node is a relay node that aggregates the messages received from its child nodes into a new message and sends it up toward the fusion center. We derive upper and lower bounds for the total error probability <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">PN</i> as explicit functions of <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">N</i> in the case where nodes and links fail with certain probabilities. These characterize the asymptotic decay rate of the total error probability as <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">N</i> goes to infinity. Naturally, this decay rate is not larger than that in the non-failure case, which is √ <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">N</i> . However, we derive an explicit necessary and sufficient condition on the decay rate of the local failure probabilities <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">pk</i> (combination of node and link failure probabilities at each level) such that the decay rate of the total error probability in the failure case is the same as that of the non-failure case. More precisely, we show that log <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">PN</i> <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-1</sup> =Θ(√ <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">N</i> ) if and only if log <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">pk</i> <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-1</sup> =Ω(2 <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">k</i> /2) .

Life prediction of different commercial dental implants as influence by uncertainties in their fatigue material properties and loading conditions

Probabilistic analyses allow the effect of uncertainty in system parameters to be determined. In the literature, many researchers have investigated static loading effects on dental implants. However, the intrinsic variability and uncertainty of most of the main problem parameters are not accounted for. The objective of this research was to apply a probabilistic computational approach to predict the fatigue life of three different commercial dental implants considering the variability and uncertainty in their fatigue material properties and loading conditions. For one of the commercial dental implants, the influence of its diameter in the fatigue life performance was also studied. This stochastic technique was based on the combination of a probabilistic finite element method (PFEM) and a cumulative damage approach known as B-model. After 6 million of loading cycles, local failure probabilities of 0.3, 0.4 and 0.91 were predicted for the Lifecore, Avinent and GMI implants, respectively (diameter of 3.75mm). The influence of the diameter for the GMI implant was studied and the results predicted a local failure probability of 0.91 and 0.1 for the 3.75mm and 5mm, respectively. In all cases the highest failure probability was located at the upper screw-threads. Therefore, the probabilistic methodology proposed herein may be a useful tool for performing a qualitative comparison between different commercial dental implants.

Predicting the Failure Probability of Device Features in MEMS

In the MEMS industry today, device reliability is commonly evaluated by simulating the loads applied to a device using finite element (FE) analysis and setting a threshold for the allowable first principal stress ( <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">S</i> <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">1</sub> ). This is a potentially misleading practice for the analysis of brittle structures, but it is used because better reliability tools have not been validated and adopted for MEMS design. In this paper, we detail and validate pragmatic FE-based MEMS analysis capabilities: local (device feature) failure probability prediction and surface-specific failure probability intensity (FPI, μm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-2</sup> ) plotting, which quantitatively identify the most probable locations of fracture on a MEMS device and provide a more meaningful and higher contrast visualization versus corresponding plots of <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">S</i> <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">1</sub> . To validate prediction effectiveness, fractographic analysis was completed on micromirrors (a representative MEMS device) loaded in two distinct complex stress states (primarily, tension or torsion) until failure, thus determining the locations of fracture initiation and their relative probabilities. Our method improves the simulation-driven design of brittle microstructures by providing not only the failure probability of the total structure but also probable failure locations as a function of load, all of which are essential for intelligent design iteration.

Hypofractionated Radiotherapy as Definitive Treatment of Stage I Non-Small Cell Lung Cancer in Older Patients

We report our experience using hypofractionated radiotherapy in older patients. This analysis includes patients aged 60 years and older at our institution with inoperable Stage I (T1/T2 N0 M0) non--small-cell lung cancer that completed a curative course of radiotherapy alone using a hypofractionated schedule. Between 1991 and 2006, 75 such patients were identified with median age of 74 years (range, 60-86). Patient characteristics were as follows: male, 65/75 (86.7%); stage IA (T1N0), 47/75 (62.7%); stage IB (T2N0), 28/75 (37.3%). Patients received a median total dose of 6500 cGy using median daily dose fractions of 250 cGy. The following outcomes were analyzed: local failure free survival (time to local failure or death from any cause), time to distal failure as first event, and overall survival. Toxicities were evaluated using Common Terminology Criteria for Adverse Events v 3.0. The median follow-up was 19.6 months (range: 4.0-128.8 months). Median local failure free survival was 19.6 months (95% confidence interval [CI]: 14.4-28.8 months); and median overall survival was 21.2 months (95% CI: 14.9-29.3 months). Analysis of competing risks showed that at 5 years, the probability of local failure as the first detected event was 22.1% (95% CI: 12.8%-32.9%); the probability of distal failure as the first detected event was 14.5% (95% CI: 7.3%-24.0%); and the probability of death without recording a failure was 48.6% (95% CI: 36.1%-60.1%). Radiation-related toxicity of grade 3 or greater was seen in 3 patients and there were no treatment-related deaths. Hypofractionated radiotherapy is an effective, safe treatment for older patients with stage I non--small-cell lung cancer.

Hypofractionated Radiotherapy for Stage I Non-small Cell Lung Carcinoma in Patients Aged 75 Years and Older

Purpose: We report our single-institution experience using hypofractionated radiotherapy in a patient population 75 years and older diagnosed with stage IA or IB (T1/T2 N0) Non-Small Cell Lung Carcinoma. Materials and methods: This is a single-institution, retrospective analysis examining disease free and overall survival and toxicity after hypofractionated radiation therapy in a patient population 75 years and older diagnosed with stage IA or IB (T1/T2 N0) NSCLC. Between 1991 and 2005, a total of 33 such patients were identified with a median age of 79 years. Patients were treated with a median total dose of 7000 cGy using median daily dose fractions of 250 cGy. Analysis of competing risks (local failure, distal failure or death as the first event) was performed and cumulative incidence functions (CIF) were estimated. Results: The median length of follow-up was 19.8 months (range: 4.3 - 103.8 months). Of the 33 patients treated, 21 (63.6% of total) had no evidence of disease recurrence on follow-up imaging over the course of the study. Of the 12 patients with disease recurrence, 6 (18.2% of total) had local failure as the first event and 6 (18.2% of total) had distant metastasis as the first event. Analysis of competing risks showed that at 5 years, the probability of local failure as the first detected event was 19.5% (95%CI: 7.6%, 35.6%); the probability of distal failure as the first detected event was 21.5% (95%CI: 7.9%,39.4%); and the probability of death without recording a failure was 44.1% (95%CI: 26.1%, 60.7%). There were no treatment related deaths reported. Conclusions: Elderly patients diagnosed with stage I non-small cell lung cancer may safely be offered hypofractionated radiotherapy as an effective option with curative intent.

Estimation of potential failure risks in a mine slope using indicator kriging

AbstractIndicator kriging has been applied to the study of failure mechanisms in a mine slope in Minas Gerais, Brazil, to estimate potential failure risks in limited areas along this slope. Timbopeba Mine, Vale Company, is an open pit iron mine situated in the Quadrilátero Ferrífero, a very important mining district in Minas Gerais. A slope excavated in quartzite with a maximum height of 200 m at the time of this study, has presented many failure problems involving the sliding of blocks formed by discontinuities. These blocks are of limited size in comparison to the dimensions of the overall slope. They appear along the entire slope, wherever discontinuity orientations have led to the kinematic feasibility of these blocks. Geostatistics permits the estimation of local failure probability distributions associated to these local failures, which would not be possible with traditional statistical models. The geostatistical method employed in this study, indicator kriging, is quite suitable because it is unnecessary to assume a particular global distribution of the phenomena being modeled. The model was used for locating areas with a great tendency for sliding failure, as it considers the local spatial variability of discontinuity orientations. Copyright © 2010 John Wiley &amp; Sons, Ltd.

Definitive Radiation Therapy for Stage I Non–Small-Cell Lung Carcinoma: Institutional Experience With Contemporary Conformal Planning

Purpose Surgical resection for stage I Non–Small-cell lung cancer (NSCLC) is not always feasible because of the high likelihood of medical comorbidity in this patient population. We report our experience using conventional and hypofractionated radiation therapy schedules with a conformal approach. Patients and Methods Between 1991 and 2006, 102 patients with medically or otherwise inoperable stage T1/T2 N0 NSCLC were treated with curative radiation therapy alone at our institution. Patients received a median total dose of 6600 cGy, with median daily dose fractions of 250 cGy. The following outcomes were analyzed: local failure-free survival (LFFS; time to local failure or death from any cause), time to local or distal failure or death as first event, and overall survival (OS). Local failure was defined as an increase in size on imaging studies. Toxicities were evaluated using Common Terminology Criteria for Adverse Events, version 3.0. Results Median follow-up was 20.9 months (range, 4.0–138.9 months). Median LFFS was 21.2 months (95% CI, 17.3–27.2 months), and median OS was 21.3 months (95% CI, 17.9–28.8 months). Analysis of competing risks showed that at 5 years, the probability of local failure as the first detected event was 15.1% (95% CI, 8.5%–23.4%), the probability of distal failure as the first detected event was 18% (95% CI, 10.9%–26.5%), and the probability of death without recording a failure was 51.6% (95% CI, 40.6%–61.5%). No patients experienced grade ≥ 4 toxicity, and only 4 patients experienced grade 3 toxicity. Conclusion Conformal radiation therapy is an effective and safe alternative to surgery for selected patients with stage I NSCLC.

Survivin Expression as a Predictive Marker for Local Control in Patients With High-Risk T1 Bladder Cancer Treated With Transurethral Resection and Radiochemotherapy

The objectives of this study were to investigate the expression of survivin in tumor samples from patients with high-risk T1 bladder cancer and to correlate its expression with clinicopathologic features as well as clinical outcomes after initial transurethral resection (TURBT) followed by radiotherapy (RT) or radiochemotherapy (RCT). Survivin protein expression was evaluated by immunohistochemistry on tumor specimen (n = 48) from the initial TURBT, and was correlated with clinical and histopathologic characteristics as well as with 5-year rates of local failure, tumor progression, and death from urothelial cancer after primary bladder sparring treatment with RT/RCT. Survivin was not expressed in normal bladder urothelium but was overexpressed in 67% of T1 tumors. No association between survivin expression and clinicopathologic factors (age, gender, grading, multifocality, associated carcinoma in situ) could be shown. With a median follow-up of 27 months (range, 3-140 months), elevated survivin expression was significantly associated with an increased probability of local failure after TURBT and RCT/RT (p = 0.003). There was also a clear trend toward a higher risk of tumor progression (p = 0.07) and lower disease-specific survival (p = 0.10). High survivin expression is a marker of tumor aggressiveness and may help to identify a subgroup of patients with T1 bladder cancer at a high risk for recurrence when treated with primary organ-sparing approaches such as TURBT and RCT.

A reliability assessment method for structural metallic component with inherent flaws based on finite element analysis and probabilistic fracture mechanics model

Reliability assessment is an essential step to promote advanced materials and components into applications. In this paper, a general reliability assessment framework was proposed to predict the lifetime distribution of a structural steel component with inherent flaws. By combining materials information, finite element analysis of the stress field and probabilistic fracture mechanics model, the distribution of failure probability subjected to fatigue loads was predicted. The local failure probability distributions identify the critical regions of the component visually. Both the global failure probability and the local failure probability distribution can be considered as essential and fundamental data in structure design and system maintenance. Focus was placed on the probabilistic fracture mechanics model and fatigue crack growth model.

Conformal Radiation Therapy as Definitive Treatment of Stage I Non—Small-Cell Lung Cancer: University of California San Diego Experience

PurposeSurgical resection remains the treatment of choice for patients with stage I non—small-cell lung cancer (NSCLC). However, there is high likelihood of medical comorbidity in this patient population, requiring management by nonsurgical approaches. We report our experience using conventional and hypofractionated radiation therapy schedules with conformal approach. Patients and MethodsBetween 1991 and 2006, 108 patients with medically or otherwise inoperable stage T1/T2 N0 NSCLC were treated with curative radiation therapy alone at our institution. Patient characteristics were as follows: median age, 73 years (range, 37–86 years); male, 88/108 (81.5%); stage T2, 46/108 (42.6%), and histology/cytology, 91/108 (84.3%). Patients received a median total dose of 6500 cGy using median daily dose fractions of 250 cGy. The majority of patients were treated using hypofractionated schedules: daily dose fractions > 200 cGy, 79/108 (73.1%). The following outcomes were analyzed: local failure-free survival (LFFS; time to local failure or death from any cause), time to local or distal failure as first event, and overall survival (OS). Local failure was defined as an increase in size on imaging studies. Toxicities were evaluated using Common Terminology Criteria for Adverse Events v3.0. ResultsMedian follow-up was 19.9 months (range, 4–138.9 months). Median LFFS was 20.8 months (95% CI, 15.1–24.3 months), and median OS was 20.9 months (95% CI, 17.1–27.2 months). Analysis of competing risks showed that, at 5 years, the probability of local failure as the first detected event was 17.1% (95% CI, 10.3–25.3%), the probability of distal failure as the first detected event was 17.9% (95% CI, 11–26.1%), and the probability of death without recording a failure was 50.7% (95% CI, 40.1–60.3%). Patients aged ≥ 70 years had higher probability of death without recording a failure within 5 years (55.5%; 95% CI, 41.7% −67.3%) than patients aged < 70 years (42.6%; 95% CI, 36.4%–58%) but similar probability of local failure as first detected event (age ≥ 70 years, 14.9%; 95% CI, 7.1%–25.1%; age < 70 years, 19.9%, 95% CI 8.9% −33.9%). There was no significant difference in LFFS when comparing tertiles of dose per fractionation or presence or absence of histology/cytology at diagnosis. No patients experienced grade ≥ 4 toxicity, and only 4 patients had grade 3 toxicity. ConclusionConformal radiation therapy is an effective and safe alternative to surgery for patients with stage I NSCLC. The results are limited because this is a single-institution observational study. Nevertheless, a large majority of patients remained free of local recurrence and without significant clinical toxicity.

Local estimation of failure probability function and its confidence interval with maximum entropy principle

An approach is developed to locally estimate the failure probability of a system under various design values. Although it seems to require numerous reliability analysis runs to locally estimate the failure probability function, which is a function of the design variables, the approach only requires a single reliability analysis run. The approach can be regarded as an extension of that proposed by Au [Au SK. Reliability-based design sensitivity by efficient simulation. Computers and Structures 2005;83(14):1048–61], but it proposes a better framework in estimating the failure probability function. The key idea is to implement the maximum entropy principle in estimating the failure probability function. The resulting local failure probability function estimate is more robust; moreover, it is possible to find the confidence interval of the failure probability function as well as estimate the gradient of the logarithm of that function with respect to the design variables. The use of the new approach is demonstrated with several simulated examples. The results show that the new approach can effectively locally estimate the failure probability function and the confidence interval with one single Subset Simulation run. Moreover, the new approach is applicable when the dimension of the uncertainties is high and when the system is highly nonlinear. The approach should be valuable for reliability-based optimization and reliability sensitivity analysis.

Three-dimensional stress analysis and Weibull statistics based strength prediction in open hole composites

Abstract The critical failure volume (CFV) method is proposed. CFV is defined as a finite subvolume in a material with general nonuniform stress distribution, which has the highest probability of failure, i.e. loss of load carrying capacity. The evaluation of the probability of failure of the subvolumes is performed based on the lowest stress and thus provides an estimate of the lower bound of the probability of local failure. An algorithm for identifying this region, based on isostress surface parameterization is proposed. It is shown that in the case of material with strength following Weibull weak link statistics such a volume exists and its location and size are defined both by the stress distribution and the scatter of strength. Moreover the probability of failure predicted by using the CFV method was found to be close to that predicted by using traditional Weibull integral method and coincide with it in the case of uniform stress fields and in the limit of zero scatter of strength. Experiments performed on homogeneous epoxy resin plaques with and without holes showed that the predictions bound the experimentally measured open hole strength. The Weibull parameters used for prediction were obtained from testing only unnotched specimens of different dimensions. The effect of the hole size on tensile strength of heterogeneous materials such as quasi-isotropic carbon–epoxy composite laminates was considered next. Fiber failure was the only failure mechanism taken into account and a strain-based failure criterion was used in the form of a two parameter Weibull distribution. The stacking sequence was selected to minimize the effect of stress redistribution due to subcritical damage. Not unexpectedly an up to 30% underprediction of the strength of the laminates with small (2.54 mm diameter) holes was observed by using classical Weibull integral method as well as Weibull based CFV method. It was explained by examining the size of the CFV, which appeared to be below Rosen’s ineffective length estimate. The CFV method was modified to account for the presence of a limit scaling size of six ineffective lengths, consistent with recent Monte-Carlo simulations by Landis et al. [Landis CM, Beyerlin IJ, McMeeking RM. Micromechanical simulation of the failure of fiber reinforced composites. Mech Phys Solids 2000;48:621–48] and was able to describe the experimentally observed magnitude of the hole size effect on composite tensile strength in the examined range of 2.54–15.24 mm hole diameters.

Transanal endoscopic versus total mesorectal laparoscopic resections of T2–N0 low rectal cancers after neoadjuvant treatment: a prospective randomized trial with a 3-years minimum follow-up period

This study aimed to compare the results and the oncologic outcomes of transanal endoscopic microsurgery (TEM) with neoadjuvant radiochemotherapy and laparoscopic resection (LR), also with neoadjuvant radiochemotherapy, in the treatment of T(2)-N(0) low rectal cancer. The study enrolled 40 patients with T2-N(0) rectal cancer, randomizing 20 to TEM (arm A) and 20 to LR (arm B). After neoadjuvant radiochemotherapy, tumor downstaging was observed for 13 patients (65%) in arm A (7 pT0 and 6 pT1) and in 11 patients (55%) in arm B (7 pT0 and 4 pT1). More than a 50% reduction of the tumor diameter was observed in four arm A cases and in six arm B cases. At a median follow-up period of 56 months (range, 44-67 months) in both arms, one local failure (5%) occurred after 6 months in arm A and one (5%) after 48 months in arm B. Distant metastases occurred in one arm A patient (5%) after 26 months of follow-up evaluation and in one arm B patient (5%) at 31 months. The probability of local or distant failure was 10% for TEM and 12% for laparoscopic resection, whereas the probability of survival was 95% for TEM and 83% for laparoscopic resection. The findings show comparative results between the two study arms in terms of probability of failure and survival.

Probabilistic Approach to Predict Cracking in Lightly Reinforced Microconcrete Panels

The ultimate strength of structures made of brittle materials—such as microconcrete—strongly depends on microstructural defects, the structure size, and the loading pattern. Probabilistic approaches allow one to take account of such dependencies. By using a Weibull model, cracking of ferrocement panels is analyzed. Provided the behavior of the reinforcement remains elastic, it is shown that the Weibull parameters identified on unreinforced microconcrete samples tested in flexure may be used to predict multiple cracking in ferrocement panels tested in tension. A key aspect of the analysis is related to the understanding and modeling of the stress heterogeneity effect on the local failure probability of unreinforced as well as reinforced microconcrete by the use of a so-called Weibull stress.

The probability of local bond failure of continuous reinforced concrete beams

This paper aims to investigate the probability of local bond failure of positive moment steels of continuous reinforced concrete beams. The probability of local bond failure is determined by the Monte Carlo technique. The random variables considered in this study are the strength of concrete, the strength of steels, the cross‐section dimensions, the concrete cover for steels, the model uncertainty of bond‐strength and the loading. The results show that increasing the parameter of transverse steels, the parameter of concrete cover for steels, and the fc ' values, the probability of local bond failure is reduced. The probability of local bond failure is below 0.00135 for most of the beams designed according to the ACI Code.

Computation and simulation of reliability parameters and their variations in heterogeneous materials

Two numerical methods for reliability assessment for composite microstructures under arbitrary loading are presented: a Monte Carlo (MC) technique that assigns discrete failure probabilities from local stresses and empirical failure probabilities, and a parametric probability product (PP) method where the joint probability of survival is from a product over a set of heterogeneous finite elements. The two methods are verified for known cases and then applied to random composite microstructures that are not amenable to direct analysis. While the MC method is computationally more expensive and less accurate than the PP method, it produces a distribution of failure predictions. The distribution places confidence intervals on survival probabilities or estimates for the number of physical experiments required to predict Weibull parameters. A composite microstructure does not have a failure distribution of the same form as its homogeneous composite parts, but its form is readily understood.